linux/kernel/workqueue.c

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/*
* kernel/workqueue.c - generic async execution with shared worker pool
*
* Copyright (C) 2002 Ingo Molnar
*
* Derived from the taskqueue/keventd code by:
* David Woodhouse <dwmw2@infradead.org>
* Andrew Morton
* Kai Petzke <wpp@marie.physik.tu-berlin.de>
* Theodore Ts'o <tytso@mit.edu>
*
* Made to use alloc_percpu by Christoph Lameter.
*
* Copyright (C) 2010 SUSE Linux Products GmbH
* Copyright (C) 2010 Tejun Heo <tj@kernel.org>
*
* This is the generic async execution mechanism. Work items as are
* executed in process context. The worker pool is shared and
* automatically managed. There are two worker pools for each CPU (one for
* normal work items and the other for high priority ones) and some extra
* pools for workqueues which are not bound to any specific CPU - the
* number of these backing pools is dynamic.
*
* Please read Documentation/workqueue.txt for details.
*/
#include <linux/export.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/signal.h>
#include <linux/completion.h>
#include <linux/workqueue.h>
#include <linux/slab.h>
#include <linux/cpu.h>
#include <linux/notifier.h>
#include <linux/kthread.h>
#include <linux/hardirq.h>
#include <linux/mempolicy.h>
#include <linux/freezer.h>
#include <linux/kallsyms.h>
#include <linux/debug_locks.h>
#include <linux/lockdep.h>
#include <linux/idr.h>
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
#include <linux/jhash.h>
#include <linux/hashtable.h>
#include <linux/rculist.h>
#include <linux/nodemask.h>
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
#include <linux/moduleparam.h>
workqueue: include workqueue info when printing debug dump of a worker task One of the problems that arise when converting dedicated custom threadpool to workqueue is that the shared worker pool used by workqueue anonimizes each worker making it more difficult to identify what the worker was doing on which target from the output of sysrq-t or debug dump from oops, BUG() and friends. This patch implements set_worker_desc() which can be called from any workqueue work function to set its description. When the worker task is dumped for whatever reason - sysrq-t, WARN, BUG, oops, lockdep assertion and so on - the description will be printed out together with the workqueue name and the worker function pointer. The printing side is implemented by print_worker_info() which is called from functions in task dump paths - sched_show_task() and dump_stack_print_info(). print_worker_info() can be safely called on any task in any state as long as the task struct itself is accessible. It uses probe_*() functions to access worker fields. It may print garbage if something went very wrong, but it wouldn't cause (another) oops. The description is currently limited to 24bytes including the terminating \0. worker->desc_valid and workder->desc[] are added and the 64 bytes marker which was already incorrect before adding the new fields is moved to the correct position. Here's an example dump with writeback updated to set the bdi name as worker desc. Hardware name: Bochs Modules linked in: Pid: 7, comm: kworker/u9:0 Not tainted 3.9.0-rc1-work+ #1 Workqueue: writeback bdi_writeback_workfn (flush-8:0) ffffffff820a3ab0 ffff88000f6e9cb8 ffffffff81c61845 ffff88000f6e9cf8 ffffffff8108f50f 0000000000000000 0000000000000000 ffff88000cde16b0 ffff88000cde1aa8 ffff88001ee19240 ffff88000f6e9fd8 ffff88000f6e9d08 Call Trace: [<ffffffff81c61845>] dump_stack+0x19/0x1b [<ffffffff8108f50f>] warn_slowpath_common+0x7f/0xc0 [<ffffffff8108f56a>] warn_slowpath_null+0x1a/0x20 [<ffffffff81200150>] bdi_writeback_workfn+0x2a0/0x3b0 ... Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com> Acked-by: Jan Kara <jack@suse.cz> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Dave Chinner <david@fromorbit.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-04-30 22:27:22 +00:00
#include <linux/uaccess.h>
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
#include "workqueue_internal.h"
enum {
/*
* worker_pool flags
2012-07-17 19:39:27 +00:00
*
* A bound pool is either associated or disassociated with its CPU.
2012-07-17 19:39:27 +00:00
* While associated (!DISASSOCIATED), all workers are bound to the
* CPU and none has %WORKER_UNBOUND set and concurrency management
* is in effect.
*
* While DISASSOCIATED, the cpu may be offline and all workers have
* %WORKER_UNBOUND set and concurrency management disabled, and may
* be executing on any CPU. The pool behaves as an unbound one.
2012-07-17 19:39:27 +00:00
*
* Note that DISASSOCIATED should be flipped only while holding
* attach_mutex to avoid changing binding state while
* worker_attach_to_pool() is in progress.
2012-07-17 19:39:27 +00:00
*/
POOL_DISASSOCIATED = 1 << 2, /* cpu can't serve workers */
/* worker flags */
WORKER_DIE = 1 << 1, /* die die die */
WORKER_IDLE = 1 << 2, /* is idle */
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
WORKER_PREP = 1 << 3, /* preparing to run works */
WORKER_CPU_INTENSIVE = 1 << 6, /* cpu intensive */
WORKER_UNBOUND = 1 << 7, /* worker is unbound */
workqueue: directly restore CPU affinity of workers from CPU_ONLINE Rebinding workers of a per-cpu pool after a CPU comes online involves a lot of back-and-forth mostly because only the task itself could adjust CPU affinity if PF_THREAD_BOUND was set. As CPU_ONLINE itself couldn't adjust affinity, it had to somehow coerce the workers themselves to perform set_cpus_allowed_ptr(). Due to the various states a worker can be in, this led to three different paths a worker may be rebound. worker->rebind_work is queued to busy workers. Idle ones are signaled by unlinking worker->entry and call idle_worker_rebind(). The manager isn't covered by either and implements its own mechanism. PF_THREAD_BOUND has been relaced with PF_NO_SETAFFINITY and CPU_ONLINE itself now can manipulate CPU affinity of workers. This patch replaces the existing rebind mechanism with direct one where CPU_ONLINE iterates over all workers using for_each_pool_worker(), restores CPU affinity, and clears WORKER_UNBOUND. There are a couple subtleties. All bound idle workers should have their runqueues set to that of the bound CPU; however, if the target task isn't running, set_cpus_allowed_ptr() just updates the cpus_allowed mask deferring the actual migration to when the task wakes up. This is worked around by waking up idle workers after restoring CPU affinity before any workers can become bound. Another subtlety is stems from matching @pool->nr_running with the number of running unbound workers. While DISASSOCIATED, all workers are unbound and nr_running is zero. As workers become bound again, nr_running needs to be adjusted accordingly; however, there is no good way to tell whether a given worker is running without poking into scheduler internals. Instead of clearing UNBOUND directly, rebind_workers() replaces UNBOUND with another new NOT_RUNNING flag - REBOUND, which will later be cleared by the workers themselves while preparing for the next round of work item execution. The only change needed for the workers is clearing REBOUND along with PREP. * This patch leaves for_each_busy_worker() without any user. Removed. * idle_worker_rebind(), busy_worker_rebind_fn(), worker->rebind_work and rebind logic in manager_workers() removed. * worker_thread() now looks at WORKER_DIE instead of testing whether @worker->entry is empty to determine whether it needs to do something special as dying is the only special thing now. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 20:45:21 +00:00
WORKER_REBOUND = 1 << 8, /* worker was rebound */
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
workqueue: directly restore CPU affinity of workers from CPU_ONLINE Rebinding workers of a per-cpu pool after a CPU comes online involves a lot of back-and-forth mostly because only the task itself could adjust CPU affinity if PF_THREAD_BOUND was set. As CPU_ONLINE itself couldn't adjust affinity, it had to somehow coerce the workers themselves to perform set_cpus_allowed_ptr(). Due to the various states a worker can be in, this led to three different paths a worker may be rebound. worker->rebind_work is queued to busy workers. Idle ones are signaled by unlinking worker->entry and call idle_worker_rebind(). The manager isn't covered by either and implements its own mechanism. PF_THREAD_BOUND has been relaced with PF_NO_SETAFFINITY and CPU_ONLINE itself now can manipulate CPU affinity of workers. This patch replaces the existing rebind mechanism with direct one where CPU_ONLINE iterates over all workers using for_each_pool_worker(), restores CPU affinity, and clears WORKER_UNBOUND. There are a couple subtleties. All bound idle workers should have their runqueues set to that of the bound CPU; however, if the target task isn't running, set_cpus_allowed_ptr() just updates the cpus_allowed mask deferring the actual migration to when the task wakes up. This is worked around by waking up idle workers after restoring CPU affinity before any workers can become bound. Another subtlety is stems from matching @pool->nr_running with the number of running unbound workers. While DISASSOCIATED, all workers are unbound and nr_running is zero. As workers become bound again, nr_running needs to be adjusted accordingly; however, there is no good way to tell whether a given worker is running without poking into scheduler internals. Instead of clearing UNBOUND directly, rebind_workers() replaces UNBOUND with another new NOT_RUNNING flag - REBOUND, which will later be cleared by the workers themselves while preparing for the next round of work item execution. The only change needed for the workers is clearing REBOUND along with PREP. * This patch leaves for_each_busy_worker() without any user. Removed. * idle_worker_rebind(), busy_worker_rebind_fn(), worker->rebind_work and rebind logic in manager_workers() removed. * worker_thread() now looks at WORKER_DIE instead of testing whether @worker->entry is empty to determine whether it needs to do something special as dying is the only special thing now. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 20:45:21 +00:00
WORKER_NOT_RUNNING = WORKER_PREP | WORKER_CPU_INTENSIVE |
WORKER_UNBOUND | WORKER_REBOUND,
NR_STD_WORKER_POOLS = 2, /* # standard pools per cpu */
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
UNBOUND_POOL_HASH_ORDER = 6, /* hashed by pool->attrs */
BUSY_WORKER_HASH_ORDER = 6, /* 64 pointers */
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
MAX_IDLE_WORKERS_RATIO = 4, /* 1/4 of busy can be idle */
IDLE_WORKER_TIMEOUT = 300 * HZ, /* keep idle ones for 5 mins */
MAYDAY_INITIAL_TIMEOUT = HZ / 100 >= 2 ? HZ / 100 : 2,
/* call for help after 10ms
(min two ticks) */
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
MAYDAY_INTERVAL = HZ / 10, /* and then every 100ms */
CREATE_COOLDOWN = HZ, /* time to breath after fail */
/*
* Rescue workers are used only on emergencies and shared by
* all cpus. Give MIN_NICE.
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
*/
RESCUER_NICE_LEVEL = MIN_NICE,
HIGHPRI_NICE_LEVEL = MIN_NICE,
WQ_NAME_LEN = 24,
};
/*
* Structure fields follow one of the following exclusion rules.
*
* I: Modifiable by initialization/destruction paths and read-only for
* everyone else.
*
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
* P: Preemption protected. Disabling preemption is enough and should
* only be modified and accessed from the local cpu.
*
* L: pool->lock protected. Access with pool->lock held.
*
* X: During normal operation, modification requires pool->lock and should
* be done only from local cpu. Either disabling preemption on local
* cpu or grabbing pool->lock is enough for read access. If
* POOL_DISASSOCIATED is set, it's identical to L.
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
*
* A: pool->attach_mutex protected.
*
* PL: wq_pool_mutex protected.
*
* PR: wq_pool_mutex protected for writes. Sched-RCU protected for reads.
*
* PW: wq_pool_mutex and wq->mutex protected for writes. Either for reads.
*
* PWR: wq_pool_mutex and wq->mutex protected for writes. Either or
* sched-RCU for reads.
*
* WQ: wq->mutex protected.
*
* WR: wq->mutex protected for writes. Sched-RCU protected for reads.
*
* MD: wq_mayday_lock protected.
*/
/* struct worker is defined in workqueue_internal.h */
struct worker_pool {
spinlock_t lock; /* the pool lock */
int cpu; /* I: the associated cpu */
int node; /* I: the associated node ID */
int id; /* I: pool ID */
unsigned int flags; /* X: flags */
workqueue: implement lockup detector Workqueue stalls can happen from a variety of usage bugs such as missing WQ_MEM_RECLAIM flag or concurrency managed work item indefinitely staying RUNNING. These stalls can be extremely difficult to hunt down because the usual warning mechanisms can't detect workqueue stalls and the internal state is pretty opaque. To alleviate the situation, this patch implements workqueue lockup detector. It periodically monitors all worker_pools periodically and, if any pool failed to make forward progress longer than the threshold duration, triggers warning and dumps workqueue state as follows. BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 31s! Showing busy workqueues and worker pools: workqueue events: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=17/256 pending: monkey_wrench_fn, e1000_watchdog, cache_reap, vmstat_shepherd, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, cgroup_release_agent workqueue events_power_efficient: flags=0x80 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=2/256 pending: check_lifetime, neigh_periodic_work workqueue cgroup_pidlist_destroy: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/1 pending: cgroup_pidlist_destroy_work_fn ... The detection mechanism is controller through kernel parameter workqueue.watchdog_thresh and can be updated at runtime through the sysfs module parameter file. v2: Decoupled from softlockup control knobs. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Don Zickus <dzickus@redhat.com> Cc: Ulrich Obergfell <uobergfe@redhat.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Chris Mason <clm@fb.com> Cc: Andrew Morton <akpm@linux-foundation.org>
2015-12-08 16:28:04 +00:00
unsigned long watchdog_ts; /* L: watchdog timestamp */
struct list_head worklist; /* L: list of pending works */
int nr_workers; /* L: total number of workers */
workqueue: reimplement idle worker rebinding Currently rebind_workers() uses rebinds idle workers synchronously before proceeding to requesting busy workers to rebind. This is necessary because all workers on @worker_pool->idle_list must be bound before concurrency management local wake-ups from the busy workers take place. Unfortunately, the synchronous idle rebinding is quite complicated. This patch reimplements idle rebinding to simplify the code path. Rather than trying to make all idle workers bound before rebinding busy workers, we simply remove all to-be-bound idle workers from the idle list and let them add themselves back after completing rebinding (successful or not). As only workers which finished rebinding can on on the idle worker list, the idle worker list is guaranteed to have only bound workers unless CPU went down again and local wake-ups are safe. After the change, @worker_pool->nr_idle may deviate than the actual number of idle workers on @worker_pool->idle_list. More specifically, nr_idle may be non-zero while ->idle_list is empty. All users of ->nr_idle and ->idle_list are audited. The only affected one is too_many_workers() which is updated to check %false if ->idle_list is empty regardless of ->nr_idle. After this patch, rebind_workers() no longer performs the nasty idle-rebind retries which require temporary release of gcwq->lock, and both unbinding and rebinding are atomic w.r.t. global_cwq->lock. worker->idle_rebind and global_cwq->rebind_hold are now unnecessary and removed along with the definition of struct idle_rebind. Changed from V1: 1) remove unlikely from too_many_workers(), ->idle_list can be empty anytime, even before this patch, no reason to use unlikely. 2) fix a small rebasing mistake. (which is from rebasing the orignal fixing patch to for-next) 3) add a lot of comments. 4) clear WORKER_REBIND unconditionaly in idle_worker_rebind() tj: Updated comments and description. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2012-09-18 16:59:22 +00:00
/* nr_idle includes the ones off idle_list for rebinding */
int nr_idle; /* L: currently idle ones */
struct list_head idle_list; /* X: list of idle workers */
struct timer_list idle_timer; /* L: worker idle timeout */
struct timer_list mayday_timer; /* L: SOS timer for workers */
/* a workers is either on busy_hash or idle_list, or the manager */
DECLARE_HASHTABLE(busy_hash, BUSY_WORKER_HASH_ORDER);
/* L: hash of busy workers */
/* see manage_workers() for details on the two manager mutexes */
struct mutex manager_arb; /* manager arbitration */
struct worker *manager; /* L: purely informational */
struct mutex attach_mutex; /* attach/detach exclusion */
struct list_head workers; /* A: attached workers */
workqueue: async worker destruction worker destruction includes these parts of code: adjust pool's stats remove the worker from idle list detach the worker from the pool kthread_stop() to wait for the worker's task exit free the worker struct We can find out that there is no essential work to do after kthread_stop(), which means destroy_worker() doesn't need to wait for the worker's task exit, so we can remove kthread_stop() and free the worker struct in the worker exiting path. However, put_unbound_pool() still needs to sync the all the workers' destruction before destroying the pool; otherwise, the workers may access to the invalid pool when they are exiting. So we also move the code of "detach the worker" to the exiting path and let put_unbound_pool() to sync with this code via detach_completion. The code of "detach the worker" is wrapped in a new function "worker_detach_from_pool()" although worker_detach_from_pool() is only called once (in worker_thread()) after this patch, but we need to wrap it for these reasons: 1) The code of "detach the worker" is not short enough to unfold them in worker_thread(). 2) the name of "worker_detach_from_pool()" is self-comment, and we add some comments above the function. 3) it will be shared by rescuer in later patch which allows rescuer and normal thread use the same attach/detach frameworks. The worker id is freed when detaching which happens before the worker is fully dead, but this id of the dying worker may be re-used for a new worker, so the dying worker's task name is changed to "worker/dying" to avoid two or several workers having the same name. Since "detach the worker" is moved out from destroy_worker(), destroy_worker() doesn't require manager_mutex, so the "lockdep_assert_held(&pool->manager_mutex)" in destroy_worker() is removed, and destroy_worker() is not protected by manager_mutex in put_unbound_pool(). tj: Minor description updates. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2014-05-20 09:46:29 +00:00
struct completion *detach_completion; /* all workers detached */
struct ida worker_ida; /* worker IDs for task name */
struct workqueue_attrs *attrs; /* I: worker attributes */
struct hlist_node hash_node; /* PL: unbound_pool_hash node */
int refcnt; /* PL: refcnt for unbound pools */
/*
* The current concurrency level. As it's likely to be accessed
* from other CPUs during try_to_wake_up(), put it in a separate
* cacheline.
*/
atomic_t nr_running ____cacheline_aligned_in_smp;
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
/*
* Destruction of pool is sched-RCU protected to allow dereferences
* from get_work_pool().
*/
struct rcu_head rcu;
} ____cacheline_aligned_in_smp;
/*
* The per-pool workqueue. While queued, the lower WORK_STRUCT_FLAG_BITS
* of work_struct->data are used for flags and the remaining high bits
* point to the pwq; thus, pwqs need to be aligned at two's power of the
* number of flag bits.
*/
struct pool_workqueue {
struct worker_pool *pool; /* I: the associated pool */
struct workqueue_struct *wq; /* I: the owning workqueue */
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
int work_color; /* L: current color */
int flush_color; /* L: flushing color */
int refcnt; /* L: reference count */
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
int nr_in_flight[WORK_NR_COLORS];
/* L: nr of in_flight works */
int nr_active; /* L: nr of active works */
int max_active; /* L: max active works */
struct list_head delayed_works; /* L: delayed works */
struct list_head pwqs_node; /* WR: node on wq->pwqs */
struct list_head mayday_node; /* MD: node on wq->maydays */
/*
* Release of unbound pwq is punted to system_wq. See put_pwq()
* and pwq_unbound_release_workfn() for details. pool_workqueue
* itself is also sched-RCU protected so that the first pwq can be
* determined without grabbing wq->mutex.
*/
struct work_struct unbound_release_work;
struct rcu_head rcu;
} __aligned(1 << WORK_STRUCT_FLAG_BITS);
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
/*
* Structure used to wait for workqueue flush.
*/
struct wq_flusher {
struct list_head list; /* WQ: list of flushers */
int flush_color; /* WQ: flush color waiting for */
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
struct completion done; /* flush completion */
};
struct wq_device;
/*
* The externally visible workqueue. It relays the issued work items to
* the appropriate worker_pool through its pool_workqueues.
*/
struct workqueue_struct {
struct list_head pwqs; /* WR: all pwqs of this wq */
struct list_head list; /* PR: list of all workqueues */
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
struct mutex mutex; /* protects this wq */
int work_color; /* WQ: current work color */
int flush_color; /* WQ: current flush color */
atomic_t nr_pwqs_to_flush; /* flush in progress */
struct wq_flusher *first_flusher; /* WQ: first flusher */
struct list_head flusher_queue; /* WQ: flush waiters */
struct list_head flusher_overflow; /* WQ: flush overflow list */
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
struct list_head maydays; /* MD: pwqs requesting rescue */
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
struct worker *rescuer; /* I: rescue worker */
int nr_drainers; /* WQ: drain in progress */
int saved_max_active; /* WQ: saved pwq max_active */
struct workqueue_attrs *unbound_attrs; /* PW: only for unbound wqs */
struct pool_workqueue *dfl_pwq; /* PW: only for unbound wqs */
#ifdef CONFIG_SYSFS
struct wq_device *wq_dev; /* I: for sysfs interface */
#endif
#ifdef CONFIG_LOCKDEP
struct lockdep_map lockdep_map;
#endif
char name[WQ_NAME_LEN]; /* I: workqueue name */
/*
* Destruction of workqueue_struct is sched-RCU protected to allow
* walking the workqueues list without grabbing wq_pool_mutex.
* This is used to dump all workqueues from sysrq.
*/
struct rcu_head rcu;
/* hot fields used during command issue, aligned to cacheline */
unsigned int flags ____cacheline_aligned; /* WQ: WQ_* flags */
struct pool_workqueue __percpu *cpu_pwqs; /* I: per-cpu pwqs */
struct pool_workqueue __rcu *numa_pwq_tbl[]; /* PWR: unbound pwqs indexed by node */
};
static struct kmem_cache *pwq_cache;
static cpumask_var_t *wq_numa_possible_cpumask;
/* possible CPUs of each node */
static bool wq_disable_numa;
module_param_named(disable_numa, wq_disable_numa, bool, 0444);
/* see the comment above the definition of WQ_POWER_EFFICIENT */
static bool wq_power_efficient = IS_ENABLED(CONFIG_WQ_POWER_EFFICIENT_DEFAULT);
module_param_named(power_efficient, wq_power_efficient, bool, 0444);
workqueue: make workqueue available early during boot Workqueue is currently initialized in an early init call; however, there are cases where early boot code has to be split and reordered to come after workqueue initialization or the same code path which makes use of workqueues is used both before workqueue initailization and after. The latter cases have to gate workqueue usages with keventd_up() tests, which is nasty and easy to get wrong. Workqueue usages have become widespread and it'd be a lot more convenient if it can be used very early from boot. This patch splits workqueue initialization into two steps. workqueue_init_early() which sets up the basic data structures so that workqueues can be created and work items queued, and workqueue_init() which actually brings up workqueues online and starts executing queued work items. The former step can be done very early during boot once memory allocation, cpumasks and idr are initialized. The latter right after kthreads become available. This allows work item queueing and canceling from very early boot which is what most of these use cases want. * As systemd_wq being initialized doesn't indicate that workqueue is fully online anymore, update keventd_up() to test wq_online instead. The follow-up patches will get rid of all its usages and the function itself. * Flushing doesn't make sense before workqueue is fully initialized. The flush functions trigger WARN and return immediately before fully online. * Work items are never in-flight before fully online. Canceling can always succeed by skipping the flush step. * Some code paths can no longer assume to be called with irq enabled as irq is disabled during early boot. Use irqsave/restore operations instead. v2: Watchdog init, which requires timer to be running, moved from workqueue_init_early() to workqueue_init(). Signed-off-by: Tejun Heo <tj@kernel.org> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/CA+55aFx0vPuMuxn00rBSM192n-Du5uxy+4AvKa0SBSOVJeuCGg@mail.gmail.com
2016-09-16 19:49:32 +00:00
bool wq_online; /* can kworkers be created yet? */
static bool wq_numa_enabled; /* unbound NUMA affinity enabled */
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
/* buf for wq_update_unbound_numa_attrs(), protected by CPU hotplug exclusion */
static struct workqueue_attrs *wq_update_unbound_numa_attrs_buf;
static DEFINE_MUTEX(wq_pool_mutex); /* protects pools and workqueues list */
static DEFINE_SPINLOCK(wq_mayday_lock); /* protects wq->maydays list */
static LIST_HEAD(workqueues); /* PR: list of all workqueues */
static bool workqueue_freezing; /* PL: have wqs started freezing? */
/* PL: allowable cpus for unbound wqs and work items */
static cpumask_var_t wq_unbound_cpumask;
/* CPU where unbound work was last round robin scheduled from this CPU */
static DEFINE_PER_CPU(int, wq_rr_cpu_last);
/*
* Local execution of unbound work items is no longer guaranteed. The
* following always forces round-robin CPU selection on unbound work items
* to uncover usages which depend on it.
*/
#ifdef CONFIG_DEBUG_WQ_FORCE_RR_CPU
static bool wq_debug_force_rr_cpu = true;
#else
static bool wq_debug_force_rr_cpu = false;
#endif
module_param_named(debug_force_rr_cpu, wq_debug_force_rr_cpu, bool, 0644);
/* the per-cpu worker pools */
tags: Fix DEFINE_PER_CPU expansions $ make tags GEN tags ctags: Warning: drivers/acpi/processor_idle.c:64: null expansion of name pattern "\1" ctags: Warning: drivers/xen/events/events_2l.c:41: null expansion of name pattern "\1" ctags: Warning: kernel/locking/lockdep.c:151: null expansion of name pattern "\1" ctags: Warning: kernel/rcu/rcutorture.c:133: null expansion of name pattern "\1" ctags: Warning: kernel/rcu/rcutorture.c:135: null expansion of name pattern "\1" ctags: Warning: kernel/workqueue.c:323: null expansion of name pattern "\1" ctags: Warning: net/ipv4/syncookies.c:53: null expansion of name pattern "\1" ctags: Warning: net/ipv6/syncookies.c:44: null expansion of name pattern "\1" ctags: Warning: net/rds/page.c:45: null expansion of name pattern "\1" Which are all the result of the DEFINE_PER_CPU pattern: scripts/tags.sh:200: '/\<DEFINE_PER_CPU([^,]*, *\([[:alnum:]_]*\)/\1/v/' scripts/tags.sh:201: '/\<DEFINE_PER_CPU_SHARED_ALIGNED([^,]*, *\([[:alnum:]_]*\)/\1/v/' The below cures them. All except the workqueue one are within reasonable distance of the 80 char limit. TJ do you have any preference on how to fix the wq one, or shall we just not care its too long? Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: David S. Miller <davem@davemloft.net> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Cc: Tejun Heo <tj@kernel.org> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-03-15 21:52:49 +00:00
static DEFINE_PER_CPU_SHARED_ALIGNED(struct worker_pool [NR_STD_WORKER_POOLS], cpu_worker_pools);
static DEFINE_IDR(worker_pool_idr); /* PR: idr of all pools */
/* PL: hash of all unbound pools keyed by pool->attrs */
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
static DEFINE_HASHTABLE(unbound_pool_hash, UNBOUND_POOL_HASH_ORDER);
/* I: attributes used when instantiating standard unbound pools on demand */
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
static struct workqueue_attrs *unbound_std_wq_attrs[NR_STD_WORKER_POOLS];
/* I: attributes used when instantiating ordered pools on demand */
static struct workqueue_attrs *ordered_wq_attrs[NR_STD_WORKER_POOLS];
struct workqueue_struct *system_wq __read_mostly;
EXPORT_SYMBOL(system_wq);
struct workqueue_struct *system_highpri_wq __read_mostly;
EXPORT_SYMBOL_GPL(system_highpri_wq);
struct workqueue_struct *system_long_wq __read_mostly;
EXPORT_SYMBOL_GPL(system_long_wq);
struct workqueue_struct *system_unbound_wq __read_mostly;
EXPORT_SYMBOL_GPL(system_unbound_wq);
struct workqueue_struct *system_freezable_wq __read_mostly;
EXPORT_SYMBOL_GPL(system_freezable_wq);
struct workqueue_struct *system_power_efficient_wq __read_mostly;
EXPORT_SYMBOL_GPL(system_power_efficient_wq);
struct workqueue_struct *system_freezable_power_efficient_wq __read_mostly;
EXPORT_SYMBOL_GPL(system_freezable_power_efficient_wq);
static int worker_thread(void *__worker);
static void workqueue_sysfs_unregister(struct workqueue_struct *wq);
#define CREATE_TRACE_POINTS
#include <trace/events/workqueue.h>
#define assert_rcu_or_pool_mutex() \
RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held() && \
!lockdep_is_held(&wq_pool_mutex), \
"sched RCU or wq_pool_mutex should be held")
#define assert_rcu_or_wq_mutex(wq) \
RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held() && \
!lockdep_is_held(&wq->mutex), \
"sched RCU or wq->mutex should be held")
#define assert_rcu_or_wq_mutex_or_pool_mutex(wq) \
RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held() && \
!lockdep_is_held(&wq->mutex) && \
!lockdep_is_held(&wq_pool_mutex), \
"sched RCU, wq->mutex or wq_pool_mutex should be held")
#define for_each_cpu_worker_pool(pool, cpu) \
for ((pool) = &per_cpu(cpu_worker_pools, cpu)[0]; \
(pool) < &per_cpu(cpu_worker_pools, cpu)[NR_STD_WORKER_POOLS]; \
(pool)++)
/**
* for_each_pool - iterate through all worker_pools in the system
* @pool: iteration cursor
* @pi: integer used for iteration
*
* This must be called either with wq_pool_mutex held or sched RCU read
* locked. If the pool needs to be used beyond the locking in effect, the
* caller is responsible for guaranteeing that the pool stays online.
*
* The if/else clause exists only for the lockdep assertion and can be
* ignored.
*/
#define for_each_pool(pool, pi) \
idr_for_each_entry(&worker_pool_idr, pool, pi) \
if (({ assert_rcu_or_pool_mutex(); false; })) { } \
else
/**
* for_each_pool_worker - iterate through all workers of a worker_pool
* @worker: iteration cursor
* @pool: worker_pool to iterate workers of
*
* This must be called with @pool->attach_mutex.
*
* The if/else clause exists only for the lockdep assertion and can be
* ignored.
*/
#define for_each_pool_worker(worker, pool) \
list_for_each_entry((worker), &(pool)->workers, node) \
if (({ lockdep_assert_held(&pool->attach_mutex); false; })) { } \
else
/**
* for_each_pwq - iterate through all pool_workqueues of the specified workqueue
* @pwq: iteration cursor
* @wq: the target workqueue
*
* This must be called either with wq->mutex held or sched RCU read locked.
* If the pwq needs to be used beyond the locking in effect, the caller is
* responsible for guaranteeing that the pwq stays online.
*
* The if/else clause exists only for the lockdep assertion and can be
* ignored.
*/
#define for_each_pwq(pwq, wq) \
list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node) \
if (({ assert_rcu_or_wq_mutex(wq); false; })) { } \
else
#ifdef CONFIG_DEBUG_OBJECTS_WORK
static struct debug_obj_descr work_debug_descr;
static void *work_debug_hint(void *addr)
{
return ((struct work_struct *) addr)->func;
}
debugobjects: insulate non-fixup logic related to static obj from fixup callbacks When activating a static object we need make sure that the object is tracked in the object tracker. If it is a non-static object then the activation is illegal. In previous implementation, each subsystem need take care of this in their fixup callbacks. Actually we can put it into debugobjects core. Thus we can save duplicated code, and have *pure* fixup callbacks. To achieve this, a new callback "is_static_object" is introduced to let the type specific code decide whether a object is static or not. If yes, we take it into object tracker, otherwise give warning and invoke fixup callback. This change has paassed debugobjects selftest, and I also do some test with all debugobjects supports enabled. At last, I have a concern about the fixups that can it change the object which is in incorrect state on fixup? Because the 'addr' may not point to any valid object if a non-static object is not tracked. Then Change such object can overwrite someone's memory and cause unexpected behaviour. For example, the timer_fixup_activate bind timer to function stub_timer. Link: http://lkml.kernel.org/r/1462576157-14539-1-git-send-email-changbin.du@intel.com [changbin.du@intel.com: improve code comments where invoke the new is_static_object callback] Link: http://lkml.kernel.org/r/1462777431-8171-1-git-send-email-changbin.du@intel.com Signed-off-by: Du, Changbin <changbin.du@intel.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Josh Triplett <josh@kernel.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tejun Heo <tj@kernel.org> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-05-20 00:09:41 +00:00
static bool work_is_static_object(void *addr)
{
struct work_struct *work = addr;
return test_bit(WORK_STRUCT_STATIC_BIT, work_data_bits(work));
}
/*
* fixup_init is called when:
* - an active object is initialized
*/
static bool work_fixup_init(void *addr, enum debug_obj_state state)
{
struct work_struct *work = addr;
switch (state) {
case ODEBUG_STATE_ACTIVE:
cancel_work_sync(work);
debug_object_init(work, &work_debug_descr);
return true;
default:
return false;
}
}
/*
* fixup_free is called when:
* - an active object is freed
*/
static bool work_fixup_free(void *addr, enum debug_obj_state state)
{
struct work_struct *work = addr;
switch (state) {
case ODEBUG_STATE_ACTIVE:
cancel_work_sync(work);
debug_object_free(work, &work_debug_descr);
return true;
default:
return false;
}
}
static struct debug_obj_descr work_debug_descr = {
.name = "work_struct",
.debug_hint = work_debug_hint,
debugobjects: insulate non-fixup logic related to static obj from fixup callbacks When activating a static object we need make sure that the object is tracked in the object tracker. If it is a non-static object then the activation is illegal. In previous implementation, each subsystem need take care of this in their fixup callbacks. Actually we can put it into debugobjects core. Thus we can save duplicated code, and have *pure* fixup callbacks. To achieve this, a new callback "is_static_object" is introduced to let the type specific code decide whether a object is static or not. If yes, we take it into object tracker, otherwise give warning and invoke fixup callback. This change has paassed debugobjects selftest, and I also do some test with all debugobjects supports enabled. At last, I have a concern about the fixups that can it change the object which is in incorrect state on fixup? Because the 'addr' may not point to any valid object if a non-static object is not tracked. Then Change such object can overwrite someone's memory and cause unexpected behaviour. For example, the timer_fixup_activate bind timer to function stub_timer. Link: http://lkml.kernel.org/r/1462576157-14539-1-git-send-email-changbin.du@intel.com [changbin.du@intel.com: improve code comments where invoke the new is_static_object callback] Link: http://lkml.kernel.org/r/1462777431-8171-1-git-send-email-changbin.du@intel.com Signed-off-by: Du, Changbin <changbin.du@intel.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Josh Triplett <josh@kernel.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tejun Heo <tj@kernel.org> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-05-20 00:09:41 +00:00
.is_static_object = work_is_static_object,
.fixup_init = work_fixup_init,
.fixup_free = work_fixup_free,
};
static inline void debug_work_activate(struct work_struct *work)
{
debug_object_activate(work, &work_debug_descr);
}
static inline void debug_work_deactivate(struct work_struct *work)
{
debug_object_deactivate(work, &work_debug_descr);
}
void __init_work(struct work_struct *work, int onstack)
{
if (onstack)
debug_object_init_on_stack(work, &work_debug_descr);
else
debug_object_init(work, &work_debug_descr);
}
EXPORT_SYMBOL_GPL(__init_work);
void destroy_work_on_stack(struct work_struct *work)
{
debug_object_free(work, &work_debug_descr);
}
EXPORT_SYMBOL_GPL(destroy_work_on_stack);
void destroy_delayed_work_on_stack(struct delayed_work *work)
{
destroy_timer_on_stack(&work->timer);
debug_object_free(&work->work, &work_debug_descr);
}
EXPORT_SYMBOL_GPL(destroy_delayed_work_on_stack);
#else
static inline void debug_work_activate(struct work_struct *work) { }
static inline void debug_work_deactivate(struct work_struct *work) { }
#endif
/**
* worker_pool_assign_id - allocate ID and assing it to @pool
* @pool: the pool pointer of interest
*
* Returns 0 if ID in [0, WORK_OFFQ_POOL_NONE) is allocated and assigned
* successfully, -errno on failure.
*/
static int worker_pool_assign_id(struct worker_pool *pool)
{
int ret;
lockdep_assert_held(&wq_pool_mutex);
ret = idr_alloc(&worker_pool_idr, pool, 0, WORK_OFFQ_POOL_NONE,
GFP_KERNEL);
Linux 3.9-rc5 -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (GNU/Linux) iQEcBAABAgAGBQJRWLTrAAoJEHm+PkMAQRiGe8oH/iMy48mecVWvxVZn74Tx3Cef xmW/PnAIj28EhSPqK49N/Ow6AfQToFKf7AP0ge20KAf5teTq95AY+tH74DAANt8F BjKXXTZiR5xwBvRkq7CR5wDcCvEcBAAz8fgTEd6SEDB2d2VXFf5eKdKUqt1avTCh Z6Hup5kuwX+ddtwY2DCBXtp2n6fL0Rm5yLzY1A3OOBye1E7VyLTF7M5BR603Q44P 4kRLxn8+R7jy3hTuZIhAeoS8TKUoBwVk7DmKxEzrhTHZVOmvwE9lEHybRnIyOpd/ k1JnbRbiPsLsCVFOn10SQkGDAIk00lro3tuWP2C1ljERiD/OOh5Ui9nXYAhMkbI= =q15K -----END PGP SIGNATURE----- Merge tag 'v3.9-rc5' into wq/for-3.10 Writeback conversion to workqueue will be based on top of wq/for-3.10 branch to take advantage of custom attrs and NUMA support for unbound workqueues. Mainline currently contains two commits which result in non-trivial merge conflicts with wq/for-3.10 and because block/for-3.10/core is based on v3.9-rc3 which contains one of the conflicting commits, we need a pre-merge-window merge anyway. Let's pull v3.9-rc5 into wq/for-3.10 so that the block tree doesn't suffer from workqueue merge conflicts. The two conflicts and their resolutions: * e68035fb65 ("workqueue: convert to idr_alloc()") in mainline changes worker_pool_assign_id() to use idr_alloc() instead of the old idr interface. worker_pool_assign_id() goes through multiple locking changes in wq/for-3.10 causing the following conflict. static int worker_pool_assign_id(struct worker_pool *pool) { int ret; <<<<<<< HEAD lockdep_assert_held(&wq_pool_mutex); do { if (!idr_pre_get(&worker_pool_idr, GFP_KERNEL)) return -ENOMEM; ret = idr_get_new(&worker_pool_idr, pool, &pool->id); } while (ret == -EAGAIN); ======= mutex_lock(&worker_pool_idr_mutex); ret = idr_alloc(&worker_pool_idr, pool, 0, 0, GFP_KERNEL); if (ret >= 0) pool->id = ret; mutex_unlock(&worker_pool_idr_mutex); >>>>>>> c67bf5361e7e66a0ff1f4caf95f89347d55dfb89 return ret < 0 ? ret : 0; } We want locking from the former and idr_alloc() usage from the latter, which can be combined to the following. static int worker_pool_assign_id(struct worker_pool *pool) { int ret; lockdep_assert_held(&wq_pool_mutex); ret = idr_alloc(&worker_pool_idr, pool, 0, 0, GFP_KERNEL); if (ret >= 0) { pool->id = ret; return 0; } return ret; } * eb2834285c ("workqueue: fix possible pool stall bug in wq_unbind_fn()") updated wq_unbind_fn() such that it has single larger for_each_std_worker_pool() loop instead of two separate loops with a schedule() call inbetween. wq/for-3.10 renamed pool->assoc_mutex to pool->manager_mutex causing the following conflict (earlier function body and comments omitted for brevity). static void wq_unbind_fn(struct work_struct *work) { ... spin_unlock_irq(&pool->lock); <<<<<<< HEAD mutex_unlock(&pool->manager_mutex); } ======= mutex_unlock(&pool->assoc_mutex); >>>>>>> c67bf5361e7e66a0ff1f4caf95f89347d55dfb89 schedule(); <<<<<<< HEAD for_each_cpu_worker_pool(pool, cpu) ======= >>>>>>> c67bf5361e7e66a0ff1f4caf95f89347d55dfb89 atomic_set(&pool->nr_running, 0); spin_lock_irq(&pool->lock); wake_up_worker(pool); spin_unlock_irq(&pool->lock); } } The resolution is mostly trivial. We want the control flow of the latter with the rename of the former. static void wq_unbind_fn(struct work_struct *work) { ... spin_unlock_irq(&pool->lock); mutex_unlock(&pool->manager_mutex); schedule(); atomic_set(&pool->nr_running, 0); spin_lock_irq(&pool->lock); wake_up_worker(pool); spin_unlock_irq(&pool->lock); } } Signed-off-by: Tejun Heo <tj@kernel.org>
2013-04-02 00:08:13 +00:00
if (ret >= 0) {
pool->id = ret;
Linux 3.9-rc5 -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (GNU/Linux) iQEcBAABAgAGBQJRWLTrAAoJEHm+PkMAQRiGe8oH/iMy48mecVWvxVZn74Tx3Cef xmW/PnAIj28EhSPqK49N/Ow6AfQToFKf7AP0ge20KAf5teTq95AY+tH74DAANt8F BjKXXTZiR5xwBvRkq7CR5wDcCvEcBAAz8fgTEd6SEDB2d2VXFf5eKdKUqt1avTCh Z6Hup5kuwX+ddtwY2DCBXtp2n6fL0Rm5yLzY1A3OOBye1E7VyLTF7M5BR603Q44P 4kRLxn8+R7jy3hTuZIhAeoS8TKUoBwVk7DmKxEzrhTHZVOmvwE9lEHybRnIyOpd/ k1JnbRbiPsLsCVFOn10SQkGDAIk00lro3tuWP2C1ljERiD/OOh5Ui9nXYAhMkbI= =q15K -----END PGP SIGNATURE----- Merge tag 'v3.9-rc5' into wq/for-3.10 Writeback conversion to workqueue will be based on top of wq/for-3.10 branch to take advantage of custom attrs and NUMA support for unbound workqueues. Mainline currently contains two commits which result in non-trivial merge conflicts with wq/for-3.10 and because block/for-3.10/core is based on v3.9-rc3 which contains one of the conflicting commits, we need a pre-merge-window merge anyway. Let's pull v3.9-rc5 into wq/for-3.10 so that the block tree doesn't suffer from workqueue merge conflicts. The two conflicts and their resolutions: * e68035fb65 ("workqueue: convert to idr_alloc()") in mainline changes worker_pool_assign_id() to use idr_alloc() instead of the old idr interface. worker_pool_assign_id() goes through multiple locking changes in wq/for-3.10 causing the following conflict. static int worker_pool_assign_id(struct worker_pool *pool) { int ret; <<<<<<< HEAD lockdep_assert_held(&wq_pool_mutex); do { if (!idr_pre_get(&worker_pool_idr, GFP_KERNEL)) return -ENOMEM; ret = idr_get_new(&worker_pool_idr, pool, &pool->id); } while (ret == -EAGAIN); ======= mutex_lock(&worker_pool_idr_mutex); ret = idr_alloc(&worker_pool_idr, pool, 0, 0, GFP_KERNEL); if (ret >= 0) pool->id = ret; mutex_unlock(&worker_pool_idr_mutex); >>>>>>> c67bf5361e7e66a0ff1f4caf95f89347d55dfb89 return ret < 0 ? ret : 0; } We want locking from the former and idr_alloc() usage from the latter, which can be combined to the following. static int worker_pool_assign_id(struct worker_pool *pool) { int ret; lockdep_assert_held(&wq_pool_mutex); ret = idr_alloc(&worker_pool_idr, pool, 0, 0, GFP_KERNEL); if (ret >= 0) { pool->id = ret; return 0; } return ret; } * eb2834285c ("workqueue: fix possible pool stall bug in wq_unbind_fn()") updated wq_unbind_fn() such that it has single larger for_each_std_worker_pool() loop instead of two separate loops with a schedule() call inbetween. wq/for-3.10 renamed pool->assoc_mutex to pool->manager_mutex causing the following conflict (earlier function body and comments omitted for brevity). static void wq_unbind_fn(struct work_struct *work) { ... spin_unlock_irq(&pool->lock); <<<<<<< HEAD mutex_unlock(&pool->manager_mutex); } ======= mutex_unlock(&pool->assoc_mutex); >>>>>>> c67bf5361e7e66a0ff1f4caf95f89347d55dfb89 schedule(); <<<<<<< HEAD for_each_cpu_worker_pool(pool, cpu) ======= >>>>>>> c67bf5361e7e66a0ff1f4caf95f89347d55dfb89 atomic_set(&pool->nr_running, 0); spin_lock_irq(&pool->lock); wake_up_worker(pool); spin_unlock_irq(&pool->lock); } } The resolution is mostly trivial. We want the control flow of the latter with the rename of the former. static void wq_unbind_fn(struct work_struct *work) { ... spin_unlock_irq(&pool->lock); mutex_unlock(&pool->manager_mutex); schedule(); atomic_set(&pool->nr_running, 0); spin_lock_irq(&pool->lock); wake_up_worker(pool); spin_unlock_irq(&pool->lock); } } Signed-off-by: Tejun Heo <tj@kernel.org>
2013-04-02 00:08:13 +00:00
return 0;
}
return ret;
}
/**
* unbound_pwq_by_node - return the unbound pool_workqueue for the given node
* @wq: the target workqueue
* @node: the node ID
*
* This must be called with any of wq_pool_mutex, wq->mutex or sched RCU
* read locked.
* If the pwq needs to be used beyond the locking in effect, the caller is
* responsible for guaranteeing that the pwq stays online.
*
* Return: The unbound pool_workqueue for @node.
*/
static struct pool_workqueue *unbound_pwq_by_node(struct workqueue_struct *wq,
int node)
{
assert_rcu_or_wq_mutex_or_pool_mutex(wq);
workqueue: handle NUMA_NO_NODE for unbound pool_workqueue lookup When looking up the pool_workqueue to use for an unbound workqueue, workqueue assumes that the target CPU is always bound to a valid NUMA node. However, currently, when a CPU goes offline, the mapping is destroyed and cpu_to_node() returns NUMA_NO_NODE. This has always been broken but hasn't triggered often enough before 874bbfe600a6 ("workqueue: make sure delayed work run in local cpu"). After the commit, workqueue forcifully assigns the local CPU for delayed work items without explicit target CPU to fix a different issue. This widens the window where CPU can go offline while a delayed work item is pending causing delayed work items dispatched with target CPU set to an already offlined CPU. The resulting NUMA_NO_NODE mapping makes workqueue try to queue the work item on a NULL pool_workqueue and thus crash. While 874bbfe600a6 has been reverted for a different reason making the bug less visible again, it can still happen. Fix it by mapping NUMA_NO_NODE to the default pool_workqueue from unbound_pwq_by_node(). This is a temporary workaround. The long term solution is keeping CPU -> NODE mapping stable across CPU off/online cycles which is being worked on. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Mike Galbraith <umgwanakikbuti@gmail.com> Cc: Tang Chen <tangchen@cn.fujitsu.com> Cc: Rafael J. Wysocki <rafael@kernel.org> Cc: Len Brown <len.brown@intel.com> Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/g/1454424264.11183.46.camel@gmail.com Link: http://lkml.kernel.org/g/1453702100-2597-1-git-send-email-tangchen@cn.fujitsu.com
2016-02-03 18:54:25 +00:00
/*
* XXX: @node can be NUMA_NO_NODE if CPU goes offline while a
* delayed item is pending. The plan is to keep CPU -> NODE
* mapping valid and stable across CPU on/offlines. Once that
* happens, this workaround can be removed.
*/
if (unlikely(node == NUMA_NO_NODE))
return wq->dfl_pwq;
return rcu_dereference_raw(wq->numa_pwq_tbl[node]);
}
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
static unsigned int work_color_to_flags(int color)
{
return color << WORK_STRUCT_COLOR_SHIFT;
}
static int get_work_color(struct work_struct *work)
{
return (*work_data_bits(work) >> WORK_STRUCT_COLOR_SHIFT) &
((1 << WORK_STRUCT_COLOR_BITS) - 1);
}
static int work_next_color(int color)
{
return (color + 1) % WORK_NR_COLORS;
}
/*
* While queued, %WORK_STRUCT_PWQ is set and non flag bits of a work's data
* contain the pointer to the queued pwq. Once execution starts, the flag
* is cleared and the high bits contain OFFQ flags and pool ID.
*
* set_work_pwq(), set_work_pool_and_clear_pending(), mark_work_canceling()
* and clear_work_data() can be used to set the pwq, pool or clear
workqueue: mark a work item being canceled as such There can be two reasons try_to_grab_pending() can fail with -EAGAIN. One is when someone else is queueing or deqeueing the work item. With the previous patches, it is guaranteed that PENDING and queued state will soon agree making it safe to busy-retry in this case. The other is if multiple __cancel_work_timer() invocations are racing one another. __cancel_work_timer() grabs PENDING and then waits for running instances of the target work item on all CPUs while holding PENDING and !queued. try_to_grab_pending() invoked from another task will keep returning -EAGAIN while the current owner is waiting. Not distinguishing the two cases is okay because __cancel_work_timer() is the only user of try_to_grab_pending() and it invokes wait_on_work() whenever grabbing fails. For the first case, busy looping should be fine but wait_on_work() doesn't cause any critical problem. For the latter case, the new contender usually waits for the same condition as the current owner, so no unnecessarily extended busy-looping happens. Combined, these make __cancel_work_timer() technically correct even without irq protection while grabbing PENDING or distinguishing the two different cases. While the current code is technically correct, not distinguishing the two cases makes it difficult to use try_to_grab_pending() for other purposes than canceling because it's impossible to tell whether it's safe to busy-retry grabbing. This patch adds a mechanism to mark a work item being canceled. try_to_grab_pending() now disables irq on success and returns -EAGAIN to indicate that grabbing failed but PENDING and queued states are gonna agree soon and it's safe to busy-loop. It returns -ENOENT if the work item is being canceled and it may stay PENDING && !queued for arbitrary amount of time. __cancel_work_timer() is modified to mark the work canceling with WORK_OFFQ_CANCELING after grabbing PENDING, thus making try_to_grab_pending() fail with -ENOENT instead of -EAGAIN. Also, it invokes wait_on_work() iff grabbing failed with -ENOENT. This isn't necessary for correctness but makes it consistent with other future users of try_to_grab_pending(). v2: try_to_grab_pending() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Updated so that try_to_grab_pending() disables irq on success rather than requiring preemption disabled by the caller. This makes busy-looping easier and will allow try_to_grap_pending() to be used from bh/irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:46 +00:00
* work->data. These functions should only be called while the work is
* owned - ie. while the PENDING bit is set.
*
* get_work_pool() and get_work_pwq() can be used to obtain the pool or pwq
* corresponding to a work. Pool is available once the work has been
* queued anywhere after initialization until it is sync canceled. pwq is
* available only while the work item is queued.
*
workqueue: mark a work item being canceled as such There can be two reasons try_to_grab_pending() can fail with -EAGAIN. One is when someone else is queueing or deqeueing the work item. With the previous patches, it is guaranteed that PENDING and queued state will soon agree making it safe to busy-retry in this case. The other is if multiple __cancel_work_timer() invocations are racing one another. __cancel_work_timer() grabs PENDING and then waits for running instances of the target work item on all CPUs while holding PENDING and !queued. try_to_grab_pending() invoked from another task will keep returning -EAGAIN while the current owner is waiting. Not distinguishing the two cases is okay because __cancel_work_timer() is the only user of try_to_grab_pending() and it invokes wait_on_work() whenever grabbing fails. For the first case, busy looping should be fine but wait_on_work() doesn't cause any critical problem. For the latter case, the new contender usually waits for the same condition as the current owner, so no unnecessarily extended busy-looping happens. Combined, these make __cancel_work_timer() technically correct even without irq protection while grabbing PENDING or distinguishing the two different cases. While the current code is technically correct, not distinguishing the two cases makes it difficult to use try_to_grab_pending() for other purposes than canceling because it's impossible to tell whether it's safe to busy-retry grabbing. This patch adds a mechanism to mark a work item being canceled. try_to_grab_pending() now disables irq on success and returns -EAGAIN to indicate that grabbing failed but PENDING and queued states are gonna agree soon and it's safe to busy-loop. It returns -ENOENT if the work item is being canceled and it may stay PENDING && !queued for arbitrary amount of time. __cancel_work_timer() is modified to mark the work canceling with WORK_OFFQ_CANCELING after grabbing PENDING, thus making try_to_grab_pending() fail with -ENOENT instead of -EAGAIN. Also, it invokes wait_on_work() iff grabbing failed with -ENOENT. This isn't necessary for correctness but makes it consistent with other future users of try_to_grab_pending(). v2: try_to_grab_pending() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Updated so that try_to_grab_pending() disables irq on success rather than requiring preemption disabled by the caller. This makes busy-looping easier and will allow try_to_grap_pending() to be used from bh/irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:46 +00:00
* %WORK_OFFQ_CANCELING is used to mark a work item which is being
* canceled. While being canceled, a work item may have its PENDING set
* but stay off timer and worklist for arbitrarily long and nobody should
* try to steal the PENDING bit.
*/
static inline void set_work_data(struct work_struct *work, unsigned long data,
unsigned long flags)
{
WARN_ON_ONCE(!work_pending(work));
atomic_long_set(&work->data, data | flags | work_static(work));
}
static void set_work_pwq(struct work_struct *work, struct pool_workqueue *pwq,
unsigned long extra_flags)
{
set_work_data(work, (unsigned long)pwq,
WORK_STRUCT_PENDING | WORK_STRUCT_PWQ | extra_flags);
}
static void set_work_pool_and_keep_pending(struct work_struct *work,
int pool_id)
{
set_work_data(work, (unsigned long)pool_id << WORK_OFFQ_POOL_SHIFT,
WORK_STRUCT_PENDING);
}
static void set_work_pool_and_clear_pending(struct work_struct *work,
int pool_id)
{
/*
* The following wmb is paired with the implied mb in
* test_and_set_bit(PENDING) and ensures all updates to @work made
* here are visible to and precede any updates by the next PENDING
* owner.
*/
smp_wmb();
set_work_data(work, (unsigned long)pool_id << WORK_OFFQ_POOL_SHIFT, 0);
workqueue: fix ghost PENDING flag while doing MQ IO The bug in a workqueue leads to a stalled IO request in MQ ctx->rq_list with the following backtrace: [ 601.347452] INFO: task kworker/u129:5:1636 blocked for more than 120 seconds. [ 601.347574] Tainted: G O 4.4.5-1-storage+ #6 [ 601.347651] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 601.348142] kworker/u129:5 D ffff880803077988 0 1636 2 0x00000000 [ 601.348519] Workqueue: ibnbd_server_fileio_wq ibnbd_dev_file_submit_io_worker [ibnbd_server] [ 601.348999] ffff880803077988 ffff88080466b900 ffff8808033f9c80 ffff880803078000 [ 601.349662] ffff880807c95000 7fffffffffffffff ffffffff815b0920 ffff880803077ad0 [ 601.350333] ffff8808030779a0 ffffffff815b01d5 0000000000000000 ffff880803077a38 [ 601.350965] Call Trace: [ 601.351203] [<ffffffff815b0920>] ? bit_wait+0x60/0x60 [ 601.351444] [<ffffffff815b01d5>] schedule+0x35/0x80 [ 601.351709] [<ffffffff815b2dd2>] schedule_timeout+0x192/0x230 [ 601.351958] [<ffffffff812d43f7>] ? blk_flush_plug_list+0xc7/0x220 [ 601.352208] [<ffffffff810bd737>] ? ktime_get+0x37/0xa0 [ 601.352446] [<ffffffff815b0920>] ? bit_wait+0x60/0x60 [ 601.352688] [<ffffffff815af784>] io_schedule_timeout+0xa4/0x110 [ 601.352951] [<ffffffff815b3a4e>] ? _raw_spin_unlock_irqrestore+0xe/0x10 [ 601.353196] [<ffffffff815b093b>] bit_wait_io+0x1b/0x70 [ 601.353440] [<ffffffff815b056d>] __wait_on_bit+0x5d/0x90 [ 601.353689] [<ffffffff81127bd0>] wait_on_page_bit+0xc0/0xd0 [ 601.353958] [<ffffffff81096db0>] ? autoremove_wake_function+0x40/0x40 [ 601.354200] [<ffffffff81127cc4>] __filemap_fdatawait_range+0xe4/0x140 [ 601.354441] [<ffffffff81127d34>] filemap_fdatawait_range+0x14/0x30 [ 601.354688] [<ffffffff81129a9f>] filemap_write_and_wait_range+0x3f/0x70 [ 601.354932] [<ffffffff811ced3b>] blkdev_fsync+0x1b/0x50 [ 601.355193] [<ffffffff811c82d9>] vfs_fsync_range+0x49/0xa0 [ 601.355432] [<ffffffff811cf45a>] blkdev_write_iter+0xca/0x100 [ 601.355679] [<ffffffff81197b1a>] __vfs_write+0xaa/0xe0 [ 601.355925] [<ffffffff81198379>] vfs_write+0xa9/0x1a0 [ 601.356164] [<ffffffff811c59d8>] kernel_write+0x38/0x50 The underlying device is a null_blk, with default parameters: queue_mode = MQ submit_queues = 1 Verification that nullb0 has something inflight: root@pserver8:~# cat /sys/block/nullb0/inflight 0 1 root@pserver8:~# find /sys/block/nullb0/mq/0/cpu* -name rq_list -print -exec cat {} \; ... /sys/block/nullb0/mq/0/cpu2/rq_list CTX pending: ffff8838038e2400 ... During debug it became clear that stalled request is always inserted in the rq_list from the following path: save_stack_trace_tsk + 34 blk_mq_insert_requests + 231 blk_mq_flush_plug_list + 281 blk_flush_plug_list + 199 wait_on_page_bit + 192 __filemap_fdatawait_range + 228 filemap_fdatawait_range + 20 filemap_write_and_wait_range + 63 blkdev_fsync + 27 vfs_fsync_range + 73 blkdev_write_iter + 202 __vfs_write + 170 vfs_write + 169 kernel_write + 56 So blk_flush_plug_list() was called with from_schedule == true. If from_schedule is true, that means that finally blk_mq_insert_requests() offloads execution of __blk_mq_run_hw_queue() and uses kblockd workqueue, i.e. it calls kblockd_schedule_delayed_work_on(). That means, that we race with another CPU, which is about to execute __blk_mq_run_hw_queue() work. Further debugging shows the following traces from different CPUs: CPU#0 CPU#1 ---------------------------------- ------------------------------- reqeust A inserted STORE hctx->ctx_map[0] bit marked kblockd_schedule...() returns 1 <schedule to kblockd workqueue> request B inserted STORE hctx->ctx_map[1] bit marked kblockd_schedule...() returns 0 *** WORK PENDING bit is cleared *** flush_busy_ctxs() is executed, but bit 1, set by CPU#1, is not observed As a result request B pended forever. This behaviour can be explained by speculative LOAD of hctx->ctx_map on CPU#0, which is reordered with clear of PENDING bit and executed _before_ actual STORE of bit 1 on CPU#1. The proper fix is an explicit full barrier <mfence>, which guarantees that clear of PENDING bit is to be executed before all possible speculative LOADS or STORES inside actual work function. Signed-off-by: Roman Pen <roman.penyaev@profitbricks.com> Cc: Gioh Kim <gi-oh.kim@profitbricks.com> Cc: Michael Wang <yun.wang@profitbricks.com> Cc: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: linux-block@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org Signed-off-by: Tejun Heo <tj@kernel.org>
2016-04-26 11:15:35 +00:00
/*
* The following mb guarantees that previous clear of a PENDING bit
* will not be reordered with any speculative LOADS or STORES from
* work->current_func, which is executed afterwards. This possible
* reordering can lead to a missed execution on attempt to qeueue
* the same @work. E.g. consider this case:
*
* CPU#0 CPU#1
* ---------------------------- --------------------------------
*
* 1 STORE event_indicated
* 2 queue_work_on() {
* 3 test_and_set_bit(PENDING)
* 4 } set_..._and_clear_pending() {
* 5 set_work_data() # clear bit
* 6 smp_mb()
* 7 work->current_func() {
* 8 LOAD event_indicated
* }
*
* Without an explicit full barrier speculative LOAD on line 8 can
* be executed before CPU#0 does STORE on line 1. If that happens,
* CPU#0 observes the PENDING bit is still set and new execution of
* a @work is not queued in a hope, that CPU#1 will eventually
* finish the queued @work. Meanwhile CPU#1 does not see
* event_indicated is set, because speculative LOAD was executed
* before actual STORE.
*/
smp_mb();
}
static void clear_work_data(struct work_struct *work)
{
smp_wmb(); /* see set_work_pool_and_clear_pending() */
set_work_data(work, WORK_STRUCT_NO_POOL, 0);
}
static struct pool_workqueue *get_work_pwq(struct work_struct *work)
{
unsigned long data = atomic_long_read(&work->data);
if (data & WORK_STRUCT_PWQ)
return (void *)(data & WORK_STRUCT_WQ_DATA_MASK);
else
return NULL;
}
/**
* get_work_pool - return the worker_pool a given work was associated with
* @work: the work item of interest
*
* Pools are created and destroyed under wq_pool_mutex, and allows read
* access under sched-RCU read lock. As such, this function should be
* called under wq_pool_mutex or with preemption disabled.
*
* All fields of the returned pool are accessible as long as the above
* mentioned locking is in effect. If the returned pool needs to be used
* beyond the critical section, the caller is responsible for ensuring the
* returned pool is and stays online.
*
* Return: The worker_pool @work was last associated with. %NULL if none.
*/
static struct worker_pool *get_work_pool(struct work_struct *work)
{
unsigned long data = atomic_long_read(&work->data);
int pool_id;
assert_rcu_or_pool_mutex();
if (data & WORK_STRUCT_PWQ)
return ((struct pool_workqueue *)
(data & WORK_STRUCT_WQ_DATA_MASK))->pool;
pool_id = data >> WORK_OFFQ_POOL_SHIFT;
if (pool_id == WORK_OFFQ_POOL_NONE)
return NULL;
return idr_find(&worker_pool_idr, pool_id);
}
/**
* get_work_pool_id - return the worker pool ID a given work is associated with
* @work: the work item of interest
*
* Return: The worker_pool ID @work was last associated with.
* %WORK_OFFQ_POOL_NONE if none.
*/
static int get_work_pool_id(struct work_struct *work)
{
unsigned long data = atomic_long_read(&work->data);
if (data & WORK_STRUCT_PWQ)
return ((struct pool_workqueue *)
(data & WORK_STRUCT_WQ_DATA_MASK))->pool->id;
return data >> WORK_OFFQ_POOL_SHIFT;
}
workqueue: mark a work item being canceled as such There can be two reasons try_to_grab_pending() can fail with -EAGAIN. One is when someone else is queueing or deqeueing the work item. With the previous patches, it is guaranteed that PENDING and queued state will soon agree making it safe to busy-retry in this case. The other is if multiple __cancel_work_timer() invocations are racing one another. __cancel_work_timer() grabs PENDING and then waits for running instances of the target work item on all CPUs while holding PENDING and !queued. try_to_grab_pending() invoked from another task will keep returning -EAGAIN while the current owner is waiting. Not distinguishing the two cases is okay because __cancel_work_timer() is the only user of try_to_grab_pending() and it invokes wait_on_work() whenever grabbing fails. For the first case, busy looping should be fine but wait_on_work() doesn't cause any critical problem. For the latter case, the new contender usually waits for the same condition as the current owner, so no unnecessarily extended busy-looping happens. Combined, these make __cancel_work_timer() technically correct even without irq protection while grabbing PENDING or distinguishing the two different cases. While the current code is technically correct, not distinguishing the two cases makes it difficult to use try_to_grab_pending() for other purposes than canceling because it's impossible to tell whether it's safe to busy-retry grabbing. This patch adds a mechanism to mark a work item being canceled. try_to_grab_pending() now disables irq on success and returns -EAGAIN to indicate that grabbing failed but PENDING and queued states are gonna agree soon and it's safe to busy-loop. It returns -ENOENT if the work item is being canceled and it may stay PENDING && !queued for arbitrary amount of time. __cancel_work_timer() is modified to mark the work canceling with WORK_OFFQ_CANCELING after grabbing PENDING, thus making try_to_grab_pending() fail with -ENOENT instead of -EAGAIN. Also, it invokes wait_on_work() iff grabbing failed with -ENOENT. This isn't necessary for correctness but makes it consistent with other future users of try_to_grab_pending(). v2: try_to_grab_pending() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Updated so that try_to_grab_pending() disables irq on success rather than requiring preemption disabled by the caller. This makes busy-looping easier and will allow try_to_grap_pending() to be used from bh/irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:46 +00:00
static void mark_work_canceling(struct work_struct *work)
{
unsigned long pool_id = get_work_pool_id(work);
workqueue: mark a work item being canceled as such There can be two reasons try_to_grab_pending() can fail with -EAGAIN. One is when someone else is queueing or deqeueing the work item. With the previous patches, it is guaranteed that PENDING and queued state will soon agree making it safe to busy-retry in this case. The other is if multiple __cancel_work_timer() invocations are racing one another. __cancel_work_timer() grabs PENDING and then waits for running instances of the target work item on all CPUs while holding PENDING and !queued. try_to_grab_pending() invoked from another task will keep returning -EAGAIN while the current owner is waiting. Not distinguishing the two cases is okay because __cancel_work_timer() is the only user of try_to_grab_pending() and it invokes wait_on_work() whenever grabbing fails. For the first case, busy looping should be fine but wait_on_work() doesn't cause any critical problem. For the latter case, the new contender usually waits for the same condition as the current owner, so no unnecessarily extended busy-looping happens. Combined, these make __cancel_work_timer() technically correct even without irq protection while grabbing PENDING or distinguishing the two different cases. While the current code is technically correct, not distinguishing the two cases makes it difficult to use try_to_grab_pending() for other purposes than canceling because it's impossible to tell whether it's safe to busy-retry grabbing. This patch adds a mechanism to mark a work item being canceled. try_to_grab_pending() now disables irq on success and returns -EAGAIN to indicate that grabbing failed but PENDING and queued states are gonna agree soon and it's safe to busy-loop. It returns -ENOENT if the work item is being canceled and it may stay PENDING && !queued for arbitrary amount of time. __cancel_work_timer() is modified to mark the work canceling with WORK_OFFQ_CANCELING after grabbing PENDING, thus making try_to_grab_pending() fail with -ENOENT instead of -EAGAIN. Also, it invokes wait_on_work() iff grabbing failed with -ENOENT. This isn't necessary for correctness but makes it consistent with other future users of try_to_grab_pending(). v2: try_to_grab_pending() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Updated so that try_to_grab_pending() disables irq on success rather than requiring preemption disabled by the caller. This makes busy-looping easier and will allow try_to_grap_pending() to be used from bh/irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:46 +00:00
pool_id <<= WORK_OFFQ_POOL_SHIFT;
set_work_data(work, pool_id | WORK_OFFQ_CANCELING, WORK_STRUCT_PENDING);
workqueue: mark a work item being canceled as such There can be two reasons try_to_grab_pending() can fail with -EAGAIN. One is when someone else is queueing or deqeueing the work item. With the previous patches, it is guaranteed that PENDING and queued state will soon agree making it safe to busy-retry in this case. The other is if multiple __cancel_work_timer() invocations are racing one another. __cancel_work_timer() grabs PENDING and then waits for running instances of the target work item on all CPUs while holding PENDING and !queued. try_to_grab_pending() invoked from another task will keep returning -EAGAIN while the current owner is waiting. Not distinguishing the two cases is okay because __cancel_work_timer() is the only user of try_to_grab_pending() and it invokes wait_on_work() whenever grabbing fails. For the first case, busy looping should be fine but wait_on_work() doesn't cause any critical problem. For the latter case, the new contender usually waits for the same condition as the current owner, so no unnecessarily extended busy-looping happens. Combined, these make __cancel_work_timer() technically correct even without irq protection while grabbing PENDING or distinguishing the two different cases. While the current code is technically correct, not distinguishing the two cases makes it difficult to use try_to_grab_pending() for other purposes than canceling because it's impossible to tell whether it's safe to busy-retry grabbing. This patch adds a mechanism to mark a work item being canceled. try_to_grab_pending() now disables irq on success and returns -EAGAIN to indicate that grabbing failed but PENDING and queued states are gonna agree soon and it's safe to busy-loop. It returns -ENOENT if the work item is being canceled and it may stay PENDING && !queued for arbitrary amount of time. __cancel_work_timer() is modified to mark the work canceling with WORK_OFFQ_CANCELING after grabbing PENDING, thus making try_to_grab_pending() fail with -ENOENT instead of -EAGAIN. Also, it invokes wait_on_work() iff grabbing failed with -ENOENT. This isn't necessary for correctness but makes it consistent with other future users of try_to_grab_pending(). v2: try_to_grab_pending() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Updated so that try_to_grab_pending() disables irq on success rather than requiring preemption disabled by the caller. This makes busy-looping easier and will allow try_to_grap_pending() to be used from bh/irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:46 +00:00
}
static bool work_is_canceling(struct work_struct *work)
{
unsigned long data = atomic_long_read(&work->data);
return !(data & WORK_STRUCT_PWQ) && (data & WORK_OFFQ_CANCELING);
workqueue: mark a work item being canceled as such There can be two reasons try_to_grab_pending() can fail with -EAGAIN. One is when someone else is queueing or deqeueing the work item. With the previous patches, it is guaranteed that PENDING and queued state will soon agree making it safe to busy-retry in this case. The other is if multiple __cancel_work_timer() invocations are racing one another. __cancel_work_timer() grabs PENDING and then waits for running instances of the target work item on all CPUs while holding PENDING and !queued. try_to_grab_pending() invoked from another task will keep returning -EAGAIN while the current owner is waiting. Not distinguishing the two cases is okay because __cancel_work_timer() is the only user of try_to_grab_pending() and it invokes wait_on_work() whenever grabbing fails. For the first case, busy looping should be fine but wait_on_work() doesn't cause any critical problem. For the latter case, the new contender usually waits for the same condition as the current owner, so no unnecessarily extended busy-looping happens. Combined, these make __cancel_work_timer() technically correct even without irq protection while grabbing PENDING or distinguishing the two different cases. While the current code is technically correct, not distinguishing the two cases makes it difficult to use try_to_grab_pending() for other purposes than canceling because it's impossible to tell whether it's safe to busy-retry grabbing. This patch adds a mechanism to mark a work item being canceled. try_to_grab_pending() now disables irq on success and returns -EAGAIN to indicate that grabbing failed but PENDING and queued states are gonna agree soon and it's safe to busy-loop. It returns -ENOENT if the work item is being canceled and it may stay PENDING && !queued for arbitrary amount of time. __cancel_work_timer() is modified to mark the work canceling with WORK_OFFQ_CANCELING after grabbing PENDING, thus making try_to_grab_pending() fail with -ENOENT instead of -EAGAIN. Also, it invokes wait_on_work() iff grabbing failed with -ENOENT. This isn't necessary for correctness but makes it consistent with other future users of try_to_grab_pending(). v2: try_to_grab_pending() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Updated so that try_to_grab_pending() disables irq on success rather than requiring preemption disabled by the caller. This makes busy-looping easier and will allow try_to_grap_pending() to be used from bh/irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:46 +00:00
}
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
/*
* Policy functions. These define the policies on how the global worker
* pools are managed. Unless noted otherwise, these functions assume that
* they're being called with pool->lock held.
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
*/
static bool __need_more_worker(struct worker_pool *pool)
{
return !atomic_read(&pool->nr_running);
}
[PATCH] WorkStruct: Use direct assignment rather than cmpxchg() Use direct assignment rather than cmpxchg() as the latter is unavailable and unimplementable on some platforms and is actually unnecessary. The use of cmpxchg() was to guard against two possibilities, neither of which can actually occur: (1) The pending flag may have been unset or may be cleared. However, given where it's called, the pending flag is _always_ set. I don't think it can be unset whilst we're in set_wq_data(). Once the work is enqueued to be actually run, the only way off the queue is for it to be actually run. If it's a delayed work item, then the bit can't be cleared by the timer because we haven't started the timer yet. Also, the pending bit can't be cleared by cancelling the delayed work _until_ the work item has had its timer started. (2) The workqueue pointer might change. This can only happen in two cases: (a) The work item has just been queued to actually run, and so we're protected by the appropriate workqueue spinlock. (b) A delayed work item is being queued, and so the timer hasn't been started yet, and so no one else knows about the work item or can access it (the pending bit protects us). Besides, set_wq_data() _sets_ the workqueue pointer unconditionally, so it can be assigned instead. So, replacing the set_wq_data() with a straight assignment would be okay in most cases. The problem is where we end up tangling with test_and_set_bit() emulated using spinlocks, and even then it's not a problem _provided_ test_and_set_bit() doesn't attempt to modify the word if the bit was set. If that's a problem, then a bitops-proofed assignment will be required - equivalent to atomic_set() vs other atomic_xxx() ops. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-12-07 11:33:26 +00:00
/*
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
* Need to wake up a worker? Called from anything but currently
* running workers.
*
* Note that, because unbound workers never contribute to nr_running, this
* function will always return %true for unbound pools as long as the
* worklist isn't empty.
[PATCH] WorkStruct: Use direct assignment rather than cmpxchg() Use direct assignment rather than cmpxchg() as the latter is unavailable and unimplementable on some platforms and is actually unnecessary. The use of cmpxchg() was to guard against two possibilities, neither of which can actually occur: (1) The pending flag may have been unset or may be cleared. However, given where it's called, the pending flag is _always_ set. I don't think it can be unset whilst we're in set_wq_data(). Once the work is enqueued to be actually run, the only way off the queue is for it to be actually run. If it's a delayed work item, then the bit can't be cleared by the timer because we haven't started the timer yet. Also, the pending bit can't be cleared by cancelling the delayed work _until_ the work item has had its timer started. (2) The workqueue pointer might change. This can only happen in two cases: (a) The work item has just been queued to actually run, and so we're protected by the appropriate workqueue spinlock. (b) A delayed work item is being queued, and so the timer hasn't been started yet, and so no one else knows about the work item or can access it (the pending bit protects us). Besides, set_wq_data() _sets_ the workqueue pointer unconditionally, so it can be assigned instead. So, replacing the set_wq_data() with a straight assignment would be okay in most cases. The problem is where we end up tangling with test_and_set_bit() emulated using spinlocks, and even then it's not a problem _provided_ test_and_set_bit() doesn't attempt to modify the word if the bit was set. If that's a problem, then a bitops-proofed assignment will be required - equivalent to atomic_set() vs other atomic_xxx() ops. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-12-07 11:33:26 +00:00
*/
static bool need_more_worker(struct worker_pool *pool)
{
return !list_empty(&pool->worklist) && __need_more_worker(pool);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
}
[PATCH] WorkStruct: Use direct assignment rather than cmpxchg() Use direct assignment rather than cmpxchg() as the latter is unavailable and unimplementable on some platforms and is actually unnecessary. The use of cmpxchg() was to guard against two possibilities, neither of which can actually occur: (1) The pending flag may have been unset or may be cleared. However, given where it's called, the pending flag is _always_ set. I don't think it can be unset whilst we're in set_wq_data(). Once the work is enqueued to be actually run, the only way off the queue is for it to be actually run. If it's a delayed work item, then the bit can't be cleared by the timer because we haven't started the timer yet. Also, the pending bit can't be cleared by cancelling the delayed work _until_ the work item has had its timer started. (2) The workqueue pointer might change. This can only happen in two cases: (a) The work item has just been queued to actually run, and so we're protected by the appropriate workqueue spinlock. (b) A delayed work item is being queued, and so the timer hasn't been started yet, and so no one else knows about the work item or can access it (the pending bit protects us). Besides, set_wq_data() _sets_ the workqueue pointer unconditionally, so it can be assigned instead. So, replacing the set_wq_data() with a straight assignment would be okay in most cases. The problem is where we end up tangling with test_and_set_bit() emulated using spinlocks, and even then it's not a problem _provided_ test_and_set_bit() doesn't attempt to modify the word if the bit was set. If that's a problem, then a bitops-proofed assignment will be required - equivalent to atomic_set() vs other atomic_xxx() ops. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-12-07 11:33:26 +00:00
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
/* Can I start working? Called from busy but !running workers. */
static bool may_start_working(struct worker_pool *pool)
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
{
return pool->nr_idle;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
}
/* Do I need to keep working? Called from currently running workers. */
static bool keep_working(struct worker_pool *pool)
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
{
return !list_empty(&pool->worklist) &&
atomic_read(&pool->nr_running) <= 1;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
}
/* Do we need a new worker? Called from manager. */
static bool need_to_create_worker(struct worker_pool *pool)
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
{
return need_more_worker(pool) && !may_start_working(pool);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
}
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
/* Do we have too many workers and should some go away? */
static bool too_many_workers(struct worker_pool *pool)
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
{
bool managing = mutex_is_locked(&pool->manager_arb);
int nr_idle = pool->nr_idle + managing; /* manager is considered idle */
int nr_busy = pool->nr_workers - nr_idle;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
return nr_idle > 2 && (nr_idle - 2) * MAX_IDLE_WORKERS_RATIO >= nr_busy;
}
/*
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
* Wake up functions.
*/
/* Return the first idle worker. Safe with preemption disabled */
static struct worker *first_idle_worker(struct worker_pool *pool)
workqueue: use shared worklist and pool all workers per cpu Use gcwq->worklist instead of cwq->worklist and break the strict association between a cwq and its worker. All works queued on a cpu are queued on gcwq->worklist and processed by any available worker on the gcwq. As there no longer is strict association between a cwq and its worker, whether a work is executing can now only be determined by calling [__]find_worker_executing_work(). After this change, the only association between a cwq and its worker is that a cwq puts a worker into shared worker pool on creation and kills it on destruction. As all workqueues are still limited to max_active of one, this means that there are always at least as many workers as active works and thus there's no danger for deadlock. The break of strong association between cwqs and workers requires somewhat clumsy changes to current_is_keventd() and destroy_workqueue(). Dynamic worker pool management will remove both clumsy changes. current_is_keventd() won't be necessary at all as the only reason it exists is to avoid queueing a work from a work which will be allowed just fine. The clumsy part of destroy_workqueue() is added because a worker can only be destroyed while idle and there's no guarantee a worker is idle when its wq is going down. With dynamic pool management, workers are not associated with workqueues at all and only idle ones will be submitted to destroy_workqueue() so the code won't be necessary anymore. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:13 +00:00
{
if (unlikely(list_empty(&pool->idle_list)))
workqueue: use shared worklist and pool all workers per cpu Use gcwq->worklist instead of cwq->worklist and break the strict association between a cwq and its worker. All works queued on a cpu are queued on gcwq->worklist and processed by any available worker on the gcwq. As there no longer is strict association between a cwq and its worker, whether a work is executing can now only be determined by calling [__]find_worker_executing_work(). After this change, the only association between a cwq and its worker is that a cwq puts a worker into shared worker pool on creation and kills it on destruction. As all workqueues are still limited to max_active of one, this means that there are always at least as many workers as active works and thus there's no danger for deadlock. The break of strong association between cwqs and workers requires somewhat clumsy changes to current_is_keventd() and destroy_workqueue(). Dynamic worker pool management will remove both clumsy changes. current_is_keventd() won't be necessary at all as the only reason it exists is to avoid queueing a work from a work which will be allowed just fine. The clumsy part of destroy_workqueue() is added because a worker can only be destroyed while idle and there's no guarantee a worker is idle when its wq is going down. With dynamic pool management, workers are not associated with workqueues at all and only idle ones will be submitted to destroy_workqueue() so the code won't be necessary anymore. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:13 +00:00
return NULL;
return list_first_entry(&pool->idle_list, struct worker, entry);
workqueue: use shared worklist and pool all workers per cpu Use gcwq->worklist instead of cwq->worklist and break the strict association between a cwq and its worker. All works queued on a cpu are queued on gcwq->worklist and processed by any available worker on the gcwq. As there no longer is strict association between a cwq and its worker, whether a work is executing can now only be determined by calling [__]find_worker_executing_work(). After this change, the only association between a cwq and its worker is that a cwq puts a worker into shared worker pool on creation and kills it on destruction. As all workqueues are still limited to max_active of one, this means that there are always at least as many workers as active works and thus there's no danger for deadlock. The break of strong association between cwqs and workers requires somewhat clumsy changes to current_is_keventd() and destroy_workqueue(). Dynamic worker pool management will remove both clumsy changes. current_is_keventd() won't be necessary at all as the only reason it exists is to avoid queueing a work from a work which will be allowed just fine. The clumsy part of destroy_workqueue() is added because a worker can only be destroyed while idle and there's no guarantee a worker is idle when its wq is going down. With dynamic pool management, workers are not associated with workqueues at all and only idle ones will be submitted to destroy_workqueue() so the code won't be necessary anymore. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:13 +00:00
}
/**
* wake_up_worker - wake up an idle worker
* @pool: worker pool to wake worker from
workqueue: use shared worklist and pool all workers per cpu Use gcwq->worklist instead of cwq->worklist and break the strict association between a cwq and its worker. All works queued on a cpu are queued on gcwq->worklist and processed by any available worker on the gcwq. As there no longer is strict association between a cwq and its worker, whether a work is executing can now only be determined by calling [__]find_worker_executing_work(). After this change, the only association between a cwq and its worker is that a cwq puts a worker into shared worker pool on creation and kills it on destruction. As all workqueues are still limited to max_active of one, this means that there are always at least as many workers as active works and thus there's no danger for deadlock. The break of strong association between cwqs and workers requires somewhat clumsy changes to current_is_keventd() and destroy_workqueue(). Dynamic worker pool management will remove both clumsy changes. current_is_keventd() won't be necessary at all as the only reason it exists is to avoid queueing a work from a work which will be allowed just fine. The clumsy part of destroy_workqueue() is added because a worker can only be destroyed while idle and there's no guarantee a worker is idle when its wq is going down. With dynamic pool management, workers are not associated with workqueues at all and only idle ones will be submitted to destroy_workqueue() so the code won't be necessary anymore. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:13 +00:00
*
* Wake up the first idle worker of @pool.
workqueue: use shared worklist and pool all workers per cpu Use gcwq->worklist instead of cwq->worklist and break the strict association between a cwq and its worker. All works queued on a cpu are queued on gcwq->worklist and processed by any available worker on the gcwq. As there no longer is strict association between a cwq and its worker, whether a work is executing can now only be determined by calling [__]find_worker_executing_work(). After this change, the only association between a cwq and its worker is that a cwq puts a worker into shared worker pool on creation and kills it on destruction. As all workqueues are still limited to max_active of one, this means that there are always at least as many workers as active works and thus there's no danger for deadlock. The break of strong association between cwqs and workers requires somewhat clumsy changes to current_is_keventd() and destroy_workqueue(). Dynamic worker pool management will remove both clumsy changes. current_is_keventd() won't be necessary at all as the only reason it exists is to avoid queueing a work from a work which will be allowed just fine. The clumsy part of destroy_workqueue() is added because a worker can only be destroyed while idle and there's no guarantee a worker is idle when its wq is going down. With dynamic pool management, workers are not associated with workqueues at all and only idle ones will be submitted to destroy_workqueue() so the code won't be necessary anymore. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:13 +00:00
*
* CONTEXT:
* spin_lock_irq(pool->lock).
workqueue: use shared worklist and pool all workers per cpu Use gcwq->worklist instead of cwq->worklist and break the strict association between a cwq and its worker. All works queued on a cpu are queued on gcwq->worklist and processed by any available worker on the gcwq. As there no longer is strict association between a cwq and its worker, whether a work is executing can now only be determined by calling [__]find_worker_executing_work(). After this change, the only association between a cwq and its worker is that a cwq puts a worker into shared worker pool on creation and kills it on destruction. As all workqueues are still limited to max_active of one, this means that there are always at least as many workers as active works and thus there's no danger for deadlock. The break of strong association between cwqs and workers requires somewhat clumsy changes to current_is_keventd() and destroy_workqueue(). Dynamic worker pool management will remove both clumsy changes. current_is_keventd() won't be necessary at all as the only reason it exists is to avoid queueing a work from a work which will be allowed just fine. The clumsy part of destroy_workqueue() is added because a worker can only be destroyed while idle and there's no guarantee a worker is idle when its wq is going down. With dynamic pool management, workers are not associated with workqueues at all and only idle ones will be submitted to destroy_workqueue() so the code won't be necessary anymore. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:13 +00:00
*/
static void wake_up_worker(struct worker_pool *pool)
workqueue: use shared worklist and pool all workers per cpu Use gcwq->worklist instead of cwq->worklist and break the strict association between a cwq and its worker. All works queued on a cpu are queued on gcwq->worklist and processed by any available worker on the gcwq. As there no longer is strict association between a cwq and its worker, whether a work is executing can now only be determined by calling [__]find_worker_executing_work(). After this change, the only association between a cwq and its worker is that a cwq puts a worker into shared worker pool on creation and kills it on destruction. As all workqueues are still limited to max_active of one, this means that there are always at least as many workers as active works and thus there's no danger for deadlock. The break of strong association between cwqs and workers requires somewhat clumsy changes to current_is_keventd() and destroy_workqueue(). Dynamic worker pool management will remove both clumsy changes. current_is_keventd() won't be necessary at all as the only reason it exists is to avoid queueing a work from a work which will be allowed just fine. The clumsy part of destroy_workqueue() is added because a worker can only be destroyed while idle and there's no guarantee a worker is idle when its wq is going down. With dynamic pool management, workers are not associated with workqueues at all and only idle ones will be submitted to destroy_workqueue() so the code won't be necessary anymore. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:13 +00:00
{
struct worker *worker = first_idle_worker(pool);
workqueue: use shared worklist and pool all workers per cpu Use gcwq->worklist instead of cwq->worklist and break the strict association between a cwq and its worker. All works queued on a cpu are queued on gcwq->worklist and processed by any available worker on the gcwq. As there no longer is strict association between a cwq and its worker, whether a work is executing can now only be determined by calling [__]find_worker_executing_work(). After this change, the only association between a cwq and its worker is that a cwq puts a worker into shared worker pool on creation and kills it on destruction. As all workqueues are still limited to max_active of one, this means that there are always at least as many workers as active works and thus there's no danger for deadlock. The break of strong association between cwqs and workers requires somewhat clumsy changes to current_is_keventd() and destroy_workqueue(). Dynamic worker pool management will remove both clumsy changes. current_is_keventd() won't be necessary at all as the only reason it exists is to avoid queueing a work from a work which will be allowed just fine. The clumsy part of destroy_workqueue() is added because a worker can only be destroyed while idle and there's no guarantee a worker is idle when its wq is going down. With dynamic pool management, workers are not associated with workqueues at all and only idle ones will be submitted to destroy_workqueue() so the code won't be necessary anymore. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:13 +00:00
if (likely(worker))
wake_up_process(worker->task);
}
/**
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
* wq_worker_waking_up - a worker is waking up
* @task: task waking up
* @cpu: CPU @task is waking up to
*
* This function is called during try_to_wake_up() when a worker is
* being awoken.
*
* CONTEXT:
* spin_lock_irq(rq->lock)
*/
void wq_worker_waking_up(struct task_struct *task, int cpu)
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
{
struct worker *worker = kthread_data(task);
if (!(worker->flags & WORKER_NOT_RUNNING)) {
WARN_ON_ONCE(worker->pool->cpu != cpu);
atomic_inc(&worker->pool->nr_running);
}
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
}
/**
* wq_worker_sleeping - a worker is going to sleep
* @task: task going to sleep
*
* This function is called during schedule() when a busy worker is
* going to sleep. Worker on the same cpu can be woken up by
* returning pointer to its task.
*
* CONTEXT:
* spin_lock_irq(rq->lock)
*
* Return:
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
* Worker task on @cpu to wake up, %NULL if none.
*/
struct task_struct *wq_worker_sleeping(struct task_struct *task)
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
{
struct worker *worker = kthread_data(task), *to_wakeup = NULL;
struct worker_pool *pool;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
/*
* Rescuers, which may not have all the fields set up like normal
* workers, also reach here, let's not access anything before
* checking NOT_RUNNING.
*/
if (worker->flags & WORKER_NOT_RUNNING)
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
return NULL;
pool = worker->pool;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
/* this can only happen on the local cpu */
if (WARN_ON_ONCE(pool->cpu != raw_smp_processor_id()))
return NULL;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
/*
* The counterpart of the following dec_and_test, implied mb,
* worklist not empty test sequence is in insert_work().
* Please read comment there.
*
* NOT_RUNNING is clear. This means that we're bound to and
* running on the local cpu w/ rq lock held and preemption
* disabled, which in turn means that none else could be
* manipulating idle_list, so dereferencing idle_list without pool
* lock is safe.
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
*/
if (atomic_dec_and_test(&pool->nr_running) &&
!list_empty(&pool->worklist))
to_wakeup = first_idle_worker(pool);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
return to_wakeup ? to_wakeup->task : NULL;
}
/**
* worker_set_flags - set worker flags and adjust nr_running accordingly
* @worker: self
* @flags: flags to set
*
* Set @flags in @worker->flags and adjust nr_running accordingly.
*
* CONTEXT:
* spin_lock_irq(pool->lock)
*/
static inline void worker_set_flags(struct worker *worker, unsigned int flags)
{
struct worker_pool *pool = worker->pool;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
WARN_ON_ONCE(worker->task != current);
/* If transitioning into NOT_RUNNING, adjust nr_running. */
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
if ((flags & WORKER_NOT_RUNNING) &&
!(worker->flags & WORKER_NOT_RUNNING)) {
atomic_dec(&pool->nr_running);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
}
worker->flags |= flags;
}
/**
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
* worker_clr_flags - clear worker flags and adjust nr_running accordingly
* @worker: self
* @flags: flags to clear
*
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
* Clear @flags in @worker->flags and adjust nr_running accordingly.
*
* CONTEXT:
* spin_lock_irq(pool->lock)
*/
static inline void worker_clr_flags(struct worker *worker, unsigned int flags)
{
struct worker_pool *pool = worker->pool;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
unsigned int oflags = worker->flags;
WARN_ON_ONCE(worker->task != current);
worker->flags &= ~flags;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
/*
* If transitioning out of NOT_RUNNING, increment nr_running. Note
* that the nested NOT_RUNNING is not a noop. NOT_RUNNING is mask
* of multiple flags, not a single flag.
*/
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
if ((flags & WORKER_NOT_RUNNING) && (oflags & WORKER_NOT_RUNNING))
if (!(worker->flags & WORKER_NOT_RUNNING))
atomic_inc(&pool->nr_running);
}
/**
* find_worker_executing_work - find worker which is executing a work
* @pool: pool of interest
* @work: work to find worker for
*
* Find a worker which is executing @work on @pool by searching
* @pool->busy_hash which is keyed by the address of @work. For a worker
workqueue: consider work function when searching for busy work items To avoid executing the same work item concurrenlty, workqueue hashes currently busy workers according to their current work items and looks up the the table when it wants to execute a new work item. If there already is a worker which is executing the new work item, the new item is queued to the found worker so that it gets executed only after the current execution finishes. Unfortunately, a work item may be freed while being executed and thus recycled for different purposes. If it gets recycled for a different work item and queued while the previous execution is still in progress, workqueue may make the new work item wait for the old one although the two aren't really related in any way. In extreme cases, this false dependency may lead to deadlock although it's extremely unlikely given that there aren't too many self-freeing work item users and they usually don't wait for other work items. To alleviate the problem, record the current work function in each busy worker and match it together with the work item address in find_worker_executing_work(). While this isn't complete, it ensures that unrelated work items don't interact with each other and in the very unlikely case where a twisted wq user triggers it, it's always onto itself making the culprit easy to spot. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Andrey Isakov <andy51@gmx.ru> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=51701 Cc: stable@vger.kernel.org
2012-12-18 18:35:02 +00:00
* to match, its current execution should match the address of @work and
* its work function. This is to avoid unwanted dependency between
* unrelated work executions through a work item being recycled while still
* being executed.
*
* This is a bit tricky. A work item may be freed once its execution
* starts and nothing prevents the freed area from being recycled for
* another work item. If the same work item address ends up being reused
* before the original execution finishes, workqueue will identify the
* recycled work item as currently executing and make it wait until the
* current execution finishes, introducing an unwanted dependency.
*
* This function checks the work item address and work function to avoid
* false positives. Note that this isn't complete as one may construct a
* work function which can introduce dependency onto itself through a
* recycled work item. Well, if somebody wants to shoot oneself in the
* foot that badly, there's only so much we can do, and if such deadlock
* actually occurs, it should be easy to locate the culprit work function.
*
* CONTEXT:
* spin_lock_irq(pool->lock).
*
* Return:
* Pointer to worker which is executing @work if found, %NULL
* otherwise.
*/
static struct worker *find_worker_executing_work(struct worker_pool *pool,
struct work_struct *work)
{
struct worker *worker;
hlist: drop the node parameter from iterators I'm not sure why, but the hlist for each entry iterators were conceived list_for_each_entry(pos, head, member) The hlist ones were greedy and wanted an extra parameter: hlist_for_each_entry(tpos, pos, head, member) Why did they need an extra pos parameter? I'm not quite sure. Not only they don't really need it, it also prevents the iterator from looking exactly like the list iterator, which is unfortunate. Besides the semantic patch, there was some manual work required: - Fix up the actual hlist iterators in linux/list.h - Fix up the declaration of other iterators based on the hlist ones. - A very small amount of places were using the 'node' parameter, this was modified to use 'obj->member' instead. - Coccinelle didn't handle the hlist_for_each_entry_safe iterator properly, so those had to be fixed up manually. The semantic patch which is mostly the work of Peter Senna Tschudin is here: @@ iterator name hlist_for_each_entry, hlist_for_each_entry_continue, hlist_for_each_entry_from, hlist_for_each_entry_rcu, hlist_for_each_entry_rcu_bh, hlist_for_each_entry_continue_rcu_bh, for_each_busy_worker, ax25_uid_for_each, ax25_for_each, inet_bind_bucket_for_each, sctp_for_each_hentry, sk_for_each, sk_for_each_rcu, sk_for_each_from, sk_for_each_safe, sk_for_each_bound, hlist_for_each_entry_safe, hlist_for_each_entry_continue_rcu, nr_neigh_for_each, nr_neigh_for_each_safe, nr_node_for_each, nr_node_for_each_safe, for_each_gfn_indirect_valid_sp, for_each_gfn_sp, for_each_host; type T; expression a,c,d,e; identifier b; statement S; @@ -T b; <+... when != b ( hlist_for_each_entry(a, - b, c, d) S | hlist_for_each_entry_continue(a, - b, c) S | hlist_for_each_entry_from(a, - b, c) S | hlist_for_each_entry_rcu(a, - b, c, d) S | hlist_for_each_entry_rcu_bh(a, - b, c, d) S | hlist_for_each_entry_continue_rcu_bh(a, - b, c) S | for_each_busy_worker(a, c, - b, d) S | ax25_uid_for_each(a, - b, c) S | ax25_for_each(a, - b, c) S | inet_bind_bucket_for_each(a, - b, c) S | sctp_for_each_hentry(a, - b, c) S | sk_for_each(a, - b, c) S | sk_for_each_rcu(a, - b, c) S | sk_for_each_from -(a, b) +(a) S + sk_for_each_from(a) S | sk_for_each_safe(a, - b, c, d) S | sk_for_each_bound(a, - b, c) S | hlist_for_each_entry_safe(a, - b, c, d, e) S | hlist_for_each_entry_continue_rcu(a, - b, c) S | nr_neigh_for_each(a, - b, c) S | nr_neigh_for_each_safe(a, - b, c, d) S | nr_node_for_each(a, - b, c) S | nr_node_for_each_safe(a, - b, c, d) S | - for_each_gfn_sp(a, c, d, b) S + for_each_gfn_sp(a, c, d) S | - for_each_gfn_indirect_valid_sp(a, c, d, b) S + for_each_gfn_indirect_valid_sp(a, c, d) S | for_each_host(a, - b, c) S | for_each_host_safe(a, - b, c, d) S | for_each_mesh_entry(a, - b, c, d) S ) ...+> [akpm@linux-foundation.org: drop bogus change from net/ipv4/raw.c] [akpm@linux-foundation.org: drop bogus hunk from net/ipv6/raw.c] [akpm@linux-foundation.org: checkpatch fixes] [akpm@linux-foundation.org: fix warnings] [akpm@linux-foudnation.org: redo intrusive kvm changes] Tested-by: Peter Senna Tschudin <peter.senna@gmail.com> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Sasha Levin <sasha.levin@oracle.com> Cc: Wu Fengguang <fengguang.wu@intel.com> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Gleb Natapov <gleb@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-02-28 01:06:00 +00:00
hash_for_each_possible(pool->busy_hash, worker, hentry,
workqueue: consider work function when searching for busy work items To avoid executing the same work item concurrenlty, workqueue hashes currently busy workers according to their current work items and looks up the the table when it wants to execute a new work item. If there already is a worker which is executing the new work item, the new item is queued to the found worker so that it gets executed only after the current execution finishes. Unfortunately, a work item may be freed while being executed and thus recycled for different purposes. If it gets recycled for a different work item and queued while the previous execution is still in progress, workqueue may make the new work item wait for the old one although the two aren't really related in any way. In extreme cases, this false dependency may lead to deadlock although it's extremely unlikely given that there aren't too many self-freeing work item users and they usually don't wait for other work items. To alleviate the problem, record the current work function in each busy worker and match it together with the work item address in find_worker_executing_work(). While this isn't complete, it ensures that unrelated work items don't interact with each other and in the very unlikely case where a twisted wq user triggers it, it's always onto itself making the culprit easy to spot. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Andrey Isakov <andy51@gmx.ru> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=51701 Cc: stable@vger.kernel.org
2012-12-18 18:35:02 +00:00
(unsigned long)work)
if (worker->current_work == work &&
worker->current_func == work->func)
return worker;
return NULL;
}
/**
* move_linked_works - move linked works to a list
* @work: start of series of works to be scheduled
* @head: target list to append @work to
* @nextp: out parameter for nested worklist walking
*
* Schedule linked works starting from @work to @head. Work series to
* be scheduled starts at @work and includes any consecutive work with
* WORK_STRUCT_LINKED set in its predecessor.
*
* If @nextp is not NULL, it's updated to point to the next work of
* the last scheduled work. This allows move_linked_works() to be
* nested inside outer list_for_each_entry_safe().
*
* CONTEXT:
* spin_lock_irq(pool->lock).
*/
static void move_linked_works(struct work_struct *work, struct list_head *head,
struct work_struct **nextp)
{
struct work_struct *n;
/*
* Linked worklist will always end before the end of the list,
* use NULL for list head.
*/
list_for_each_entry_safe_from(work, n, NULL, entry) {
list_move_tail(&work->entry, head);
if (!(*work_data_bits(work) & WORK_STRUCT_LINKED))
break;
}
/*
* If we're already inside safe list traversal and have moved
* multiple works to the scheduled queue, the next position
* needs to be updated.
*/
if (nextp)
*nextp = n;
}
/**
* get_pwq - get an extra reference on the specified pool_workqueue
* @pwq: pool_workqueue to get
*
* Obtain an extra reference on @pwq. The caller should guarantee that
* @pwq has positive refcnt and be holding the matching pool->lock.
*/
static void get_pwq(struct pool_workqueue *pwq)
{
lockdep_assert_held(&pwq->pool->lock);
WARN_ON_ONCE(pwq->refcnt <= 0);
pwq->refcnt++;
}
/**
* put_pwq - put a pool_workqueue reference
* @pwq: pool_workqueue to put
*
* Drop a reference of @pwq. If its refcnt reaches zero, schedule its
* destruction. The caller should be holding the matching pool->lock.
*/
static void put_pwq(struct pool_workqueue *pwq)
{
lockdep_assert_held(&pwq->pool->lock);
if (likely(--pwq->refcnt))
return;
if (WARN_ON_ONCE(!(pwq->wq->flags & WQ_UNBOUND)))
return;
/*
* @pwq can't be released under pool->lock, bounce to
* pwq_unbound_release_workfn(). This never recurses on the same
* pool->lock as this path is taken only for unbound workqueues and
* the release work item is scheduled on a per-cpu workqueue. To
* avoid lockdep warning, unbound pool->locks are given lockdep
* subclass of 1 in get_unbound_pool().
*/
schedule_work(&pwq->unbound_release_work);
}
/**
* put_pwq_unlocked - put_pwq() with surrounding pool lock/unlock
* @pwq: pool_workqueue to put (can be %NULL)
*
* put_pwq() with locking. This function also allows %NULL @pwq.
*/
static void put_pwq_unlocked(struct pool_workqueue *pwq)
{
if (pwq) {
/*
* As both pwqs and pools are sched-RCU protected, the
* following lock operations are safe.
*/
spin_lock_irq(&pwq->pool->lock);
put_pwq(pwq);
spin_unlock_irq(&pwq->pool->lock);
}
}
static void pwq_activate_delayed_work(struct work_struct *work)
{
struct pool_workqueue *pwq = get_work_pwq(work);
trace_workqueue_activate_work(work);
workqueue: implement lockup detector Workqueue stalls can happen from a variety of usage bugs such as missing WQ_MEM_RECLAIM flag or concurrency managed work item indefinitely staying RUNNING. These stalls can be extremely difficult to hunt down because the usual warning mechanisms can't detect workqueue stalls and the internal state is pretty opaque. To alleviate the situation, this patch implements workqueue lockup detector. It periodically monitors all worker_pools periodically and, if any pool failed to make forward progress longer than the threshold duration, triggers warning and dumps workqueue state as follows. BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 31s! Showing busy workqueues and worker pools: workqueue events: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=17/256 pending: monkey_wrench_fn, e1000_watchdog, cache_reap, vmstat_shepherd, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, cgroup_release_agent workqueue events_power_efficient: flags=0x80 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=2/256 pending: check_lifetime, neigh_periodic_work workqueue cgroup_pidlist_destroy: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/1 pending: cgroup_pidlist_destroy_work_fn ... The detection mechanism is controller through kernel parameter workqueue.watchdog_thresh and can be updated at runtime through the sysfs module parameter file. v2: Decoupled from softlockup control knobs. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Don Zickus <dzickus@redhat.com> Cc: Ulrich Obergfell <uobergfe@redhat.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Chris Mason <clm@fb.com> Cc: Andrew Morton <akpm@linux-foundation.org>
2015-12-08 16:28:04 +00:00
if (list_empty(&pwq->pool->worklist))
pwq->pool->watchdog_ts = jiffies;
move_linked_works(work, &pwq->pool->worklist, NULL);
__clear_bit(WORK_STRUCT_DELAYED_BIT, work_data_bits(work));
pwq->nr_active++;
}
static void pwq_activate_first_delayed(struct pool_workqueue *pwq)
{
struct work_struct *work = list_first_entry(&pwq->delayed_works,
struct work_struct, entry);
pwq_activate_delayed_work(work);
}
/**
* pwq_dec_nr_in_flight - decrement pwq's nr_in_flight
* @pwq: pwq of interest
* @color: color of work which left the queue
*
* A work either has completed or is removed from pending queue,
* decrement nr_in_flight of its pwq and handle workqueue flushing.
*
* CONTEXT:
* spin_lock_irq(pool->lock).
*/
static void pwq_dec_nr_in_flight(struct pool_workqueue *pwq, int color)
{
/* uncolored work items don't participate in flushing or nr_active */
if (color == WORK_NO_COLOR)
goto out_put;
pwq->nr_in_flight[color]--;
pwq->nr_active--;
if (!list_empty(&pwq->delayed_works)) {
/* one down, submit a delayed one */
if (pwq->nr_active < pwq->max_active)
pwq_activate_first_delayed(pwq);
}
/* is flush in progress and are we at the flushing tip? */
if (likely(pwq->flush_color != color))
goto out_put;
/* are there still in-flight works? */
if (pwq->nr_in_flight[color])
goto out_put;
/* this pwq is done, clear flush_color */
pwq->flush_color = -1;
/*
* If this was the last pwq, wake up the first flusher. It
* will handle the rest.
*/
if (atomic_dec_and_test(&pwq->wq->nr_pwqs_to_flush))
complete(&pwq->wq->first_flusher->done);
out_put:
put_pwq(pwq);
}
/**
workqueue: mark a work item being canceled as such There can be two reasons try_to_grab_pending() can fail with -EAGAIN. One is when someone else is queueing or deqeueing the work item. With the previous patches, it is guaranteed that PENDING and queued state will soon agree making it safe to busy-retry in this case. The other is if multiple __cancel_work_timer() invocations are racing one another. __cancel_work_timer() grabs PENDING and then waits for running instances of the target work item on all CPUs while holding PENDING and !queued. try_to_grab_pending() invoked from another task will keep returning -EAGAIN while the current owner is waiting. Not distinguishing the two cases is okay because __cancel_work_timer() is the only user of try_to_grab_pending() and it invokes wait_on_work() whenever grabbing fails. For the first case, busy looping should be fine but wait_on_work() doesn't cause any critical problem. For the latter case, the new contender usually waits for the same condition as the current owner, so no unnecessarily extended busy-looping happens. Combined, these make __cancel_work_timer() technically correct even without irq protection while grabbing PENDING or distinguishing the two different cases. While the current code is technically correct, not distinguishing the two cases makes it difficult to use try_to_grab_pending() for other purposes than canceling because it's impossible to tell whether it's safe to busy-retry grabbing. This patch adds a mechanism to mark a work item being canceled. try_to_grab_pending() now disables irq on success and returns -EAGAIN to indicate that grabbing failed but PENDING and queued states are gonna agree soon and it's safe to busy-loop. It returns -ENOENT if the work item is being canceled and it may stay PENDING && !queued for arbitrary amount of time. __cancel_work_timer() is modified to mark the work canceling with WORK_OFFQ_CANCELING after grabbing PENDING, thus making try_to_grab_pending() fail with -ENOENT instead of -EAGAIN. Also, it invokes wait_on_work() iff grabbing failed with -ENOENT. This isn't necessary for correctness but makes it consistent with other future users of try_to_grab_pending(). v2: try_to_grab_pending() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Updated so that try_to_grab_pending() disables irq on success rather than requiring preemption disabled by the caller. This makes busy-looping easier and will allow try_to_grap_pending() to be used from bh/irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:46 +00:00
* try_to_grab_pending - steal work item from worklist and disable irq
* @work: work item to steal
* @is_dwork: @work is a delayed_work
workqueue: mark a work item being canceled as such There can be two reasons try_to_grab_pending() can fail with -EAGAIN. One is when someone else is queueing or deqeueing the work item. With the previous patches, it is guaranteed that PENDING and queued state will soon agree making it safe to busy-retry in this case. The other is if multiple __cancel_work_timer() invocations are racing one another. __cancel_work_timer() grabs PENDING and then waits for running instances of the target work item on all CPUs while holding PENDING and !queued. try_to_grab_pending() invoked from another task will keep returning -EAGAIN while the current owner is waiting. Not distinguishing the two cases is okay because __cancel_work_timer() is the only user of try_to_grab_pending() and it invokes wait_on_work() whenever grabbing fails. For the first case, busy looping should be fine but wait_on_work() doesn't cause any critical problem. For the latter case, the new contender usually waits for the same condition as the current owner, so no unnecessarily extended busy-looping happens. Combined, these make __cancel_work_timer() technically correct even without irq protection while grabbing PENDING or distinguishing the two different cases. While the current code is technically correct, not distinguishing the two cases makes it difficult to use try_to_grab_pending() for other purposes than canceling because it's impossible to tell whether it's safe to busy-retry grabbing. This patch adds a mechanism to mark a work item being canceled. try_to_grab_pending() now disables irq on success and returns -EAGAIN to indicate that grabbing failed but PENDING and queued states are gonna agree soon and it's safe to busy-loop. It returns -ENOENT if the work item is being canceled and it may stay PENDING && !queued for arbitrary amount of time. __cancel_work_timer() is modified to mark the work canceling with WORK_OFFQ_CANCELING after grabbing PENDING, thus making try_to_grab_pending() fail with -ENOENT instead of -EAGAIN. Also, it invokes wait_on_work() iff grabbing failed with -ENOENT. This isn't necessary for correctness but makes it consistent with other future users of try_to_grab_pending(). v2: try_to_grab_pending() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Updated so that try_to_grab_pending() disables irq on success rather than requiring preemption disabled by the caller. This makes busy-looping easier and will allow try_to_grap_pending() to be used from bh/irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:46 +00:00
* @flags: place to store irq state
*
* Try to grab PENDING bit of @work. This function can handle @work in any
* stable state - idle, on timer or on worklist.
*
* Return:
* 1 if @work was pending and we successfully stole PENDING
* 0 if @work was idle and we claimed PENDING
* -EAGAIN if PENDING couldn't be grabbed at the moment, safe to busy-retry
workqueue: mark a work item being canceled as such There can be two reasons try_to_grab_pending() can fail with -EAGAIN. One is when someone else is queueing or deqeueing the work item. With the previous patches, it is guaranteed that PENDING and queued state will soon agree making it safe to busy-retry in this case. The other is if multiple __cancel_work_timer() invocations are racing one another. __cancel_work_timer() grabs PENDING and then waits for running instances of the target work item on all CPUs while holding PENDING and !queued. try_to_grab_pending() invoked from another task will keep returning -EAGAIN while the current owner is waiting. Not distinguishing the two cases is okay because __cancel_work_timer() is the only user of try_to_grab_pending() and it invokes wait_on_work() whenever grabbing fails. For the first case, busy looping should be fine but wait_on_work() doesn't cause any critical problem. For the latter case, the new contender usually waits for the same condition as the current owner, so no unnecessarily extended busy-looping happens. Combined, these make __cancel_work_timer() technically correct even without irq protection while grabbing PENDING or distinguishing the two different cases. While the current code is technically correct, not distinguishing the two cases makes it difficult to use try_to_grab_pending() for other purposes than canceling because it's impossible to tell whether it's safe to busy-retry grabbing. This patch adds a mechanism to mark a work item being canceled. try_to_grab_pending() now disables irq on success and returns -EAGAIN to indicate that grabbing failed but PENDING and queued states are gonna agree soon and it's safe to busy-loop. It returns -ENOENT if the work item is being canceled and it may stay PENDING && !queued for arbitrary amount of time. __cancel_work_timer() is modified to mark the work canceling with WORK_OFFQ_CANCELING after grabbing PENDING, thus making try_to_grab_pending() fail with -ENOENT instead of -EAGAIN. Also, it invokes wait_on_work() iff grabbing failed with -ENOENT. This isn't necessary for correctness but makes it consistent with other future users of try_to_grab_pending(). v2: try_to_grab_pending() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Updated so that try_to_grab_pending() disables irq on success rather than requiring preemption disabled by the caller. This makes busy-looping easier and will allow try_to_grap_pending() to be used from bh/irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:46 +00:00
* -ENOENT if someone else is canceling @work, this state may persist
* for arbitrarily long
*
* Note:
workqueue: mark a work item being canceled as such There can be two reasons try_to_grab_pending() can fail with -EAGAIN. One is when someone else is queueing or deqeueing the work item. With the previous patches, it is guaranteed that PENDING and queued state will soon agree making it safe to busy-retry in this case. The other is if multiple __cancel_work_timer() invocations are racing one another. __cancel_work_timer() grabs PENDING and then waits for running instances of the target work item on all CPUs while holding PENDING and !queued. try_to_grab_pending() invoked from another task will keep returning -EAGAIN while the current owner is waiting. Not distinguishing the two cases is okay because __cancel_work_timer() is the only user of try_to_grab_pending() and it invokes wait_on_work() whenever grabbing fails. For the first case, busy looping should be fine but wait_on_work() doesn't cause any critical problem. For the latter case, the new contender usually waits for the same condition as the current owner, so no unnecessarily extended busy-looping happens. Combined, these make __cancel_work_timer() technically correct even without irq protection while grabbing PENDING or distinguishing the two different cases. While the current code is technically correct, not distinguishing the two cases makes it difficult to use try_to_grab_pending() for other purposes than canceling because it's impossible to tell whether it's safe to busy-retry grabbing. This patch adds a mechanism to mark a work item being canceled. try_to_grab_pending() now disables irq on success and returns -EAGAIN to indicate that grabbing failed but PENDING and queued states are gonna agree soon and it's safe to busy-loop. It returns -ENOENT if the work item is being canceled and it may stay PENDING && !queued for arbitrary amount of time. __cancel_work_timer() is modified to mark the work canceling with WORK_OFFQ_CANCELING after grabbing PENDING, thus making try_to_grab_pending() fail with -ENOENT instead of -EAGAIN. Also, it invokes wait_on_work() iff grabbing failed with -ENOENT. This isn't necessary for correctness but makes it consistent with other future users of try_to_grab_pending(). v2: try_to_grab_pending() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Updated so that try_to_grab_pending() disables irq on success rather than requiring preemption disabled by the caller. This makes busy-looping easier and will allow try_to_grap_pending() to be used from bh/irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:46 +00:00
* On >= 0 return, the caller owns @work's PENDING bit. To avoid getting
* interrupted while holding PENDING and @work off queue, irq must be
* disabled on entry. This, combined with delayed_work->timer being
* irqsafe, ensures that we return -EAGAIN for finite short period of time.
workqueue: mark a work item being canceled as such There can be two reasons try_to_grab_pending() can fail with -EAGAIN. One is when someone else is queueing or deqeueing the work item. With the previous patches, it is guaranteed that PENDING and queued state will soon agree making it safe to busy-retry in this case. The other is if multiple __cancel_work_timer() invocations are racing one another. __cancel_work_timer() grabs PENDING and then waits for running instances of the target work item on all CPUs while holding PENDING and !queued. try_to_grab_pending() invoked from another task will keep returning -EAGAIN while the current owner is waiting. Not distinguishing the two cases is okay because __cancel_work_timer() is the only user of try_to_grab_pending() and it invokes wait_on_work() whenever grabbing fails. For the first case, busy looping should be fine but wait_on_work() doesn't cause any critical problem. For the latter case, the new contender usually waits for the same condition as the current owner, so no unnecessarily extended busy-looping happens. Combined, these make __cancel_work_timer() technically correct even without irq protection while grabbing PENDING or distinguishing the two different cases. While the current code is technically correct, not distinguishing the two cases makes it difficult to use try_to_grab_pending() for other purposes than canceling because it's impossible to tell whether it's safe to busy-retry grabbing. This patch adds a mechanism to mark a work item being canceled. try_to_grab_pending() now disables irq on success and returns -EAGAIN to indicate that grabbing failed but PENDING and queued states are gonna agree soon and it's safe to busy-loop. It returns -ENOENT if the work item is being canceled and it may stay PENDING && !queued for arbitrary amount of time. __cancel_work_timer() is modified to mark the work canceling with WORK_OFFQ_CANCELING after grabbing PENDING, thus making try_to_grab_pending() fail with -ENOENT instead of -EAGAIN. Also, it invokes wait_on_work() iff grabbing failed with -ENOENT. This isn't necessary for correctness but makes it consistent with other future users of try_to_grab_pending(). v2: try_to_grab_pending() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Updated so that try_to_grab_pending() disables irq on success rather than requiring preemption disabled by the caller. This makes busy-looping easier and will allow try_to_grap_pending() to be used from bh/irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:46 +00:00
*
* On successful return, >= 0, irq is disabled and the caller is
* responsible for releasing it using local_irq_restore(*@flags).
*
* This function is safe to call from any context including IRQ handler.
*/
workqueue: mark a work item being canceled as such There can be two reasons try_to_grab_pending() can fail with -EAGAIN. One is when someone else is queueing or deqeueing the work item. With the previous patches, it is guaranteed that PENDING and queued state will soon agree making it safe to busy-retry in this case. The other is if multiple __cancel_work_timer() invocations are racing one another. __cancel_work_timer() grabs PENDING and then waits for running instances of the target work item on all CPUs while holding PENDING and !queued. try_to_grab_pending() invoked from another task will keep returning -EAGAIN while the current owner is waiting. Not distinguishing the two cases is okay because __cancel_work_timer() is the only user of try_to_grab_pending() and it invokes wait_on_work() whenever grabbing fails. For the first case, busy looping should be fine but wait_on_work() doesn't cause any critical problem. For the latter case, the new contender usually waits for the same condition as the current owner, so no unnecessarily extended busy-looping happens. Combined, these make __cancel_work_timer() technically correct even without irq protection while grabbing PENDING or distinguishing the two different cases. While the current code is technically correct, not distinguishing the two cases makes it difficult to use try_to_grab_pending() for other purposes than canceling because it's impossible to tell whether it's safe to busy-retry grabbing. This patch adds a mechanism to mark a work item being canceled. try_to_grab_pending() now disables irq on success and returns -EAGAIN to indicate that grabbing failed but PENDING and queued states are gonna agree soon and it's safe to busy-loop. It returns -ENOENT if the work item is being canceled and it may stay PENDING && !queued for arbitrary amount of time. __cancel_work_timer() is modified to mark the work canceling with WORK_OFFQ_CANCELING after grabbing PENDING, thus making try_to_grab_pending() fail with -ENOENT instead of -EAGAIN. Also, it invokes wait_on_work() iff grabbing failed with -ENOENT. This isn't necessary for correctness but makes it consistent with other future users of try_to_grab_pending(). v2: try_to_grab_pending() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Updated so that try_to_grab_pending() disables irq on success rather than requiring preemption disabled by the caller. This makes busy-looping easier and will allow try_to_grap_pending() to be used from bh/irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:46 +00:00
static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
unsigned long *flags)
{
struct worker_pool *pool;
struct pool_workqueue *pwq;
workqueue: mark a work item being canceled as such There can be two reasons try_to_grab_pending() can fail with -EAGAIN. One is when someone else is queueing or deqeueing the work item. With the previous patches, it is guaranteed that PENDING and queued state will soon agree making it safe to busy-retry in this case. The other is if multiple __cancel_work_timer() invocations are racing one another. __cancel_work_timer() grabs PENDING and then waits for running instances of the target work item on all CPUs while holding PENDING and !queued. try_to_grab_pending() invoked from another task will keep returning -EAGAIN while the current owner is waiting. Not distinguishing the two cases is okay because __cancel_work_timer() is the only user of try_to_grab_pending() and it invokes wait_on_work() whenever grabbing fails. For the first case, busy looping should be fine but wait_on_work() doesn't cause any critical problem. For the latter case, the new contender usually waits for the same condition as the current owner, so no unnecessarily extended busy-looping happens. Combined, these make __cancel_work_timer() technically correct even without irq protection while grabbing PENDING or distinguishing the two different cases. While the current code is technically correct, not distinguishing the two cases makes it difficult to use try_to_grab_pending() for other purposes than canceling because it's impossible to tell whether it's safe to busy-retry grabbing. This patch adds a mechanism to mark a work item being canceled. try_to_grab_pending() now disables irq on success and returns -EAGAIN to indicate that grabbing failed but PENDING and queued states are gonna agree soon and it's safe to busy-loop. It returns -ENOENT if the work item is being canceled and it may stay PENDING && !queued for arbitrary amount of time. __cancel_work_timer() is modified to mark the work canceling with WORK_OFFQ_CANCELING after grabbing PENDING, thus making try_to_grab_pending() fail with -ENOENT instead of -EAGAIN. Also, it invokes wait_on_work() iff grabbing failed with -ENOENT. This isn't necessary for correctness but makes it consistent with other future users of try_to_grab_pending(). v2: try_to_grab_pending() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Updated so that try_to_grab_pending() disables irq on success rather than requiring preemption disabled by the caller. This makes busy-looping easier and will allow try_to_grap_pending() to be used from bh/irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:46 +00:00
local_irq_save(*flags);
/* try to steal the timer if it exists */
if (is_dwork) {
struct delayed_work *dwork = to_delayed_work(work);
/*
* dwork->timer is irqsafe. If del_timer() fails, it's
* guaranteed that the timer is not queued anywhere and not
* running on the local CPU.
*/
if (likely(del_timer(&dwork->timer)))
return 1;
}
/* try to claim PENDING the normal way */
if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)))
return 0;
/*
* The queueing is in progress, or it is already queued. Try to
* steal it from ->worklist without clearing WORK_STRUCT_PENDING.
*/
pool = get_work_pool(work);
if (!pool)
workqueue: mark a work item being canceled as such There can be two reasons try_to_grab_pending() can fail with -EAGAIN. One is when someone else is queueing or deqeueing the work item. With the previous patches, it is guaranteed that PENDING and queued state will soon agree making it safe to busy-retry in this case. The other is if multiple __cancel_work_timer() invocations are racing one another. __cancel_work_timer() grabs PENDING and then waits for running instances of the target work item on all CPUs while holding PENDING and !queued. try_to_grab_pending() invoked from another task will keep returning -EAGAIN while the current owner is waiting. Not distinguishing the two cases is okay because __cancel_work_timer() is the only user of try_to_grab_pending() and it invokes wait_on_work() whenever grabbing fails. For the first case, busy looping should be fine but wait_on_work() doesn't cause any critical problem. For the latter case, the new contender usually waits for the same condition as the current owner, so no unnecessarily extended busy-looping happens. Combined, these make __cancel_work_timer() technically correct even without irq protection while grabbing PENDING or distinguishing the two different cases. While the current code is technically correct, not distinguishing the two cases makes it difficult to use try_to_grab_pending() for other purposes than canceling because it's impossible to tell whether it's safe to busy-retry grabbing. This patch adds a mechanism to mark a work item being canceled. try_to_grab_pending() now disables irq on success and returns -EAGAIN to indicate that grabbing failed but PENDING and queued states are gonna agree soon and it's safe to busy-loop. It returns -ENOENT if the work item is being canceled and it may stay PENDING && !queued for arbitrary amount of time. __cancel_work_timer() is modified to mark the work canceling with WORK_OFFQ_CANCELING after grabbing PENDING, thus making try_to_grab_pending() fail with -ENOENT instead of -EAGAIN. Also, it invokes wait_on_work() iff grabbing failed with -ENOENT. This isn't necessary for correctness but makes it consistent with other future users of try_to_grab_pending(). v2: try_to_grab_pending() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Updated so that try_to_grab_pending() disables irq on success rather than requiring preemption disabled by the caller. This makes busy-looping easier and will allow try_to_grap_pending() to be used from bh/irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:46 +00:00
goto fail;
spin_lock(&pool->lock);
workqueue: simplify is-work-item-queued-here test Currently, determining whether a work item is queued on a locked pool involves somewhat convoluted memory barrier dancing. It goes like the following. * When a work item is queued on a pool, work->data is updated before work->entry is linked to the pending list with a wmb() inbetween. * When trying to determine whether a work item is currently queued on a pool pointed to by work->data, it locks the pool and looks at work->entry. If work->entry is linked, we then do rmb() and then check whether work->data points to the current pool. This works because, work->data can only point to a pool if it currently is or were on the pool and, * If it currently is on the pool, the tests would obviously succeed. * It it left the pool, its work->entry was cleared under pool->lock, so if we're seeing non-empty work->entry, it has to be from the work item being linked on another pool. Because work->data is updated before work->entry is linked with wmb() inbetween, work->data update from another pool is guaranteed to be visible if we do rmb() after seeing non-empty work->entry. So, we either see empty work->entry or we see updated work->data pointin to another pool. While this works, it's convoluted, to put it mildly. With recent updates, it's now guaranteed that work->data points to cwq only while the work item is queued and that updating work->data to point to cwq or back to pool is done under pool->lock, so we can simply test whether work->data points to cwq which is associated with the currently locked pool instead of the convoluted memory barrier dancing. This patch replaces the memory barrier based "are you still here, really?" test with much simpler "does work->data points to me?" test - if work->data points to a cwq which is associated with the currently locked pool, the work item is guaranteed to be queued on the pool as work->data can start and stop pointing to such cwq only under pool->lock and the start and stop coincide with queue and dequeue. tj: Rewrote the comments and description. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2013-02-07 02:04:53 +00:00
/*
* work->data is guaranteed to point to pwq only while the work
* item is queued on pwq->wq, and both updating work->data to point
* to pwq on queueing and to pool on dequeueing are done under
* pwq->pool->lock. This in turn guarantees that, if work->data
* points to pwq which is associated with a locked pool, the work
workqueue: simplify is-work-item-queued-here test Currently, determining whether a work item is queued on a locked pool involves somewhat convoluted memory barrier dancing. It goes like the following. * When a work item is queued on a pool, work->data is updated before work->entry is linked to the pending list with a wmb() inbetween. * When trying to determine whether a work item is currently queued on a pool pointed to by work->data, it locks the pool and looks at work->entry. If work->entry is linked, we then do rmb() and then check whether work->data points to the current pool. This works because, work->data can only point to a pool if it currently is or were on the pool and, * If it currently is on the pool, the tests would obviously succeed. * It it left the pool, its work->entry was cleared under pool->lock, so if we're seeing non-empty work->entry, it has to be from the work item being linked on another pool. Because work->data is updated before work->entry is linked with wmb() inbetween, work->data update from another pool is guaranteed to be visible if we do rmb() after seeing non-empty work->entry. So, we either see empty work->entry or we see updated work->data pointin to another pool. While this works, it's convoluted, to put it mildly. With recent updates, it's now guaranteed that work->data points to cwq only while the work item is queued and that updating work->data to point to cwq or back to pool is done under pool->lock, so we can simply test whether work->data points to cwq which is associated with the currently locked pool instead of the convoluted memory barrier dancing. This patch replaces the memory barrier based "are you still here, really?" test with much simpler "does work->data points to me?" test - if work->data points to a cwq which is associated with the currently locked pool, the work item is guaranteed to be queued on the pool as work->data can start and stop pointing to such cwq only under pool->lock and the start and stop coincide with queue and dequeue. tj: Rewrote the comments and description. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2013-02-07 02:04:53 +00:00
* item is currently queued on that pool.
*/
pwq = get_work_pwq(work);
if (pwq && pwq->pool == pool) {
debug_work_deactivate(work);
/*
* A delayed work item cannot be grabbed directly because
* it might have linked NO_COLOR work items which, if left
* on the delayed_list, will confuse pwq->nr_active
* management later on and cause stall. Make sure the work
* item is activated before grabbing.
*/
if (*work_data_bits(work) & WORK_STRUCT_DELAYED)
pwq_activate_delayed_work(work);
list_del_init(&work->entry);
pwq_dec_nr_in_flight(pwq, get_work_color(work));
/* work->data points to pwq iff queued, point to pool */
set_work_pool_and_keep_pending(work, pool->id);
spin_unlock(&pool->lock);
return 1;
}
spin_unlock(&pool->lock);
workqueue: mark a work item being canceled as such There can be two reasons try_to_grab_pending() can fail with -EAGAIN. One is when someone else is queueing or deqeueing the work item. With the previous patches, it is guaranteed that PENDING and queued state will soon agree making it safe to busy-retry in this case. The other is if multiple __cancel_work_timer() invocations are racing one another. __cancel_work_timer() grabs PENDING and then waits for running instances of the target work item on all CPUs while holding PENDING and !queued. try_to_grab_pending() invoked from another task will keep returning -EAGAIN while the current owner is waiting. Not distinguishing the two cases is okay because __cancel_work_timer() is the only user of try_to_grab_pending() and it invokes wait_on_work() whenever grabbing fails. For the first case, busy looping should be fine but wait_on_work() doesn't cause any critical problem. For the latter case, the new contender usually waits for the same condition as the current owner, so no unnecessarily extended busy-looping happens. Combined, these make __cancel_work_timer() technically correct even without irq protection while grabbing PENDING or distinguishing the two different cases. While the current code is technically correct, not distinguishing the two cases makes it difficult to use try_to_grab_pending() for other purposes than canceling because it's impossible to tell whether it's safe to busy-retry grabbing. This patch adds a mechanism to mark a work item being canceled. try_to_grab_pending() now disables irq on success and returns -EAGAIN to indicate that grabbing failed but PENDING and queued states are gonna agree soon and it's safe to busy-loop. It returns -ENOENT if the work item is being canceled and it may stay PENDING && !queued for arbitrary amount of time. __cancel_work_timer() is modified to mark the work canceling with WORK_OFFQ_CANCELING after grabbing PENDING, thus making try_to_grab_pending() fail with -ENOENT instead of -EAGAIN. Also, it invokes wait_on_work() iff grabbing failed with -ENOENT. This isn't necessary for correctness but makes it consistent with other future users of try_to_grab_pending(). v2: try_to_grab_pending() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Updated so that try_to_grab_pending() disables irq on success rather than requiring preemption disabled by the caller. This makes busy-looping easier and will allow try_to_grap_pending() to be used from bh/irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:46 +00:00
fail:
local_irq_restore(*flags);
if (work_is_canceling(work))
return -ENOENT;
cpu_relax();
return -EAGAIN;
}
/**
* insert_work - insert a work into a pool
* @pwq: pwq @work belongs to
* @work: work to insert
* @head: insertion point
* @extra_flags: extra WORK_STRUCT_* flags to set
*
* Insert @work which belongs to @pwq after @head. @extra_flags is or'd to
* work_struct flags.
*
* CONTEXT:
* spin_lock_irq(pool->lock).
*/
static void insert_work(struct pool_workqueue *pwq, struct work_struct *work,
struct list_head *head, unsigned int extra_flags)
implement flush_work() A basic problem with flush_scheduled_work() is that it blocks behind _all_ presently-queued works, rather than just the work whcih the caller wants to flush. If the caller holds some lock, and if one of the queued work happens to want that lock as well then accidental deadlocks can occur. One example of this is the phy layer: it wants to flush work while holding rtnl_lock(). But if a linkwatch event happens to be queued, the phy code will deadlock because the linkwatch callback function takes rtnl_lock. So we implement a new function which will flush a *single* work - just the one which the caller wants to free up. Thus we avoid the accidental deadlocks which can arise from unrelated subsystems' callbacks taking shared locks. flush_work() non-blockingly dequeues the work_struct which we want to kill, then it waits for its handler to complete on all CPUs. Add ->current_work to the "struct cpu_workqueue_struct", it points to currently running "struct work_struct". When flush_work(work) detects ->current_work == work, it inserts a barrier at the _head_ of ->worklist (and thus right _after_ that work) and waits for completition. This means that the next work fired on that CPU will be this barrier, or another barrier queued by concurrent flush_work(), so the caller of flush_work() will be woken before any "regular" work has a chance to run. When wait_on_work() unlocks workqueue_mutex (or whatever we choose to protect against CPU hotplug), CPU may go away. But in that case take_over_work() will move a barrier we queued to another CPU, it will be fired sometime, and wait_on_work() will be woken. Actually, we are doing cleanup_workqueue_thread()->kthread_stop() before take_over_work(), so cwq->thread should complete its ->worklist (and thus the barrier), because currently we don't check kthread_should_stop() in run_workqueue(). But even if we did, everything should be ok. [akpm@osdl.org: cleanup] [akpm@osdl.org: add flush_work_keventd() wrapper] Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-09 09:33:52 +00:00
{
struct worker_pool *pool = pwq->pool;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
/* we own @work, set data and link */
set_work_pwq(work, pwq, extra_flags);
list_add_tail(&work->entry, head);
get_pwq(pwq);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
/*
* Ensure either wq_worker_sleeping() sees the above
* list_add_tail() or we see zero nr_running to avoid workers lying
* around lazily while there are works to be processed.
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
*/
smp_mb();
if (__need_more_worker(pool))
wake_up_worker(pool);
implement flush_work() A basic problem with flush_scheduled_work() is that it blocks behind _all_ presently-queued works, rather than just the work whcih the caller wants to flush. If the caller holds some lock, and if one of the queued work happens to want that lock as well then accidental deadlocks can occur. One example of this is the phy layer: it wants to flush work while holding rtnl_lock(). But if a linkwatch event happens to be queued, the phy code will deadlock because the linkwatch callback function takes rtnl_lock. So we implement a new function which will flush a *single* work - just the one which the caller wants to free up. Thus we avoid the accidental deadlocks which can arise from unrelated subsystems' callbacks taking shared locks. flush_work() non-blockingly dequeues the work_struct which we want to kill, then it waits for its handler to complete on all CPUs. Add ->current_work to the "struct cpu_workqueue_struct", it points to currently running "struct work_struct". When flush_work(work) detects ->current_work == work, it inserts a barrier at the _head_ of ->worklist (and thus right _after_ that work) and waits for completition. This means that the next work fired on that CPU will be this barrier, or another barrier queued by concurrent flush_work(), so the caller of flush_work() will be woken before any "regular" work has a chance to run. When wait_on_work() unlocks workqueue_mutex (or whatever we choose to protect against CPU hotplug), CPU may go away. But in that case take_over_work() will move a barrier we queued to another CPU, it will be fired sometime, and wait_on_work() will be woken. Actually, we are doing cleanup_workqueue_thread()->kthread_stop() before take_over_work(), so cwq->thread should complete its ->worklist (and thus the barrier), because currently we don't check kthread_should_stop() in run_workqueue(). But even if we did, everything should be ok. [akpm@osdl.org: cleanup] [akpm@osdl.org: add flush_work_keventd() wrapper] Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-09 09:33:52 +00:00
}
/*
* Test whether @work is being queued from another work executing on the
* same workqueue.
*/
static bool is_chained_work(struct workqueue_struct *wq)
{
struct worker *worker;
worker = current_wq_worker();
/*
* Return %true iff I'm a worker execuing a work item on @wq. If
* I'm @worker, it's safe to dereference it without locking.
*/
return worker && worker->current_pwq->wq == wq;
}
/*
* When queueing an unbound work item to a wq, prefer local CPU if allowed
* by wq_unbound_cpumask. Otherwise, round robin among the allowed ones to
* avoid perturbing sensitive tasks.
*/
static int wq_select_unbound_cpu(int cpu)
{
static bool printed_dbg_warning;
int new_cpu;
if (likely(!wq_debug_force_rr_cpu)) {
if (cpumask_test_cpu(cpu, wq_unbound_cpumask))
return cpu;
} else if (!printed_dbg_warning) {
pr_warn("workqueue: round-robin CPU selection forced, expect performance impact\n");
printed_dbg_warning = true;
}
if (cpumask_empty(wq_unbound_cpumask))
return cpu;
new_cpu = __this_cpu_read(wq_rr_cpu_last);
new_cpu = cpumask_next_and(new_cpu, wq_unbound_cpumask, cpu_online_mask);
if (unlikely(new_cpu >= nr_cpu_ids)) {
new_cpu = cpumask_first_and(wq_unbound_cpumask, cpu_online_mask);
if (unlikely(new_cpu >= nr_cpu_ids))
return cpu;
}
__this_cpu_write(wq_rr_cpu_last, new_cpu);
return new_cpu;
}
static void __queue_work(int cpu, struct workqueue_struct *wq,
struct work_struct *work)
{
struct pool_workqueue *pwq;
struct worker_pool *last_pool;
struct list_head *worklist;
unsigned int work_flags;
unsigned int req_cpu = cpu;
workqueue: disable irq while manipulating PENDING Queueing operations use WORK_STRUCT_PENDING_BIT to synchronize access to the target work item. They first try to claim the bit and proceed with queueing only after that succeeds and there's a window between PENDING being set and the actual queueing where the task can be interrupted or preempted. There's also a similar window in process_one_work() when clearing PENDING. A work item is dequeued, gcwq->lock is released and then PENDING is cleared and the worker might get interrupted or preempted between releasing gcwq->lock and clearing PENDING. cancel[_delayed]_work_sync() tries to claim or steal PENDING. The function assumes that a work item with PENDING is either queued or in the process of being [de]queued. In the latter case, it busy-loops until either the work item loses PENDING or is queued. If canceling coincides with the above described interrupts or preemptions, the canceling task will busy-loop while the queueing or executing task is preempted. This patch keeps irq disabled across claiming PENDING and actual queueing and moves PENDING clearing in process_one_work() inside gcwq->lock so that busy looping from PENDING && !queued doesn't wait for interrupted/preempted tasks. Note that, in process_one_work(), setting last CPU and clearing PENDING got merged into single operation. This removes possible long busy-loops and will allow using try_to_grab_pending() from bh and irq contexts. v2: __queue_work() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Disable irq instead of preemption. IRQ will be disabled while grabbing gcwq->lock later anyway and this allows using try_to_grab_pending() from bh and irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:45 +00:00
/*
* While a work item is PENDING && off queue, a task trying to
* steal the PENDING will busy-loop waiting for it to either get
* queued or lose PENDING. Grabbing PENDING and queueing should
* happen with IRQ disabled.
*/
WARN_ON_ONCE(!irqs_disabled());
debug_work_activate(work);
/* if draining, only works from the same workqueue are allowed */
if (unlikely(wq->flags & __WQ_DRAINING) &&
WARN_ON_ONCE(!is_chained_work(wq)))
return;
retry:
if (req_cpu == WORK_CPU_UNBOUND)
cpu = wq_select_unbound_cpu(raw_smp_processor_id());
/* pwq which will be used unless @work is executing elsewhere */
if (!(wq->flags & WQ_UNBOUND))
pwq = per_cpu_ptr(wq->cpu_pwqs, cpu);
else
pwq = unbound_pwq_by_node(wq, cpu_to_node(cpu));
workqueue: make all workqueues non-reentrant By default, each per-cpu part of a bound workqueue operates separately and a work item may be executing concurrently on different CPUs. The behavior avoids some cross-cpu traffic but leads to subtle weirdities and not-so-subtle contortions in the API. * There's no sane usefulness in allowing a single work item to be executed concurrently on multiple CPUs. People just get the behavior unintentionally and get surprised after learning about it. Most either explicitly synchronize or use non-reentrant/ordered workqueue but this is error-prone. * flush_work() can't wait for multiple instances of the same work item on different CPUs. If a work item is executing on cpu0 and then queued on cpu1, flush_work() can only wait for the one on cpu1. Unfortunately, work items can easily cross CPU boundaries unintentionally when the queueing thread gets migrated. This means that if multiple queuers compete, flush_work() can't even guarantee that the instance queued right before it is finished before returning. * flush_work_sync() was added to work around some of the deficiencies of flush_work(). In addition to the usual flushing, it ensures that all currently executing instances are finished before returning. This operation is expensive as it has to walk all CPUs and at the same time fails to address competing queuer case. Incorrectly using flush_work() when flush_work_sync() is necessary is an easy error to make and can lead to bugs which are difficult to reproduce. * Similar problems exist for flush_delayed_work[_sync](). Other than the cross-cpu access concern, there's no benefit in allowing parallel execution and it's plain silly to have this level of contortion for workqueue which is widely used from core code to extremely obscure drivers. This patch makes all workqueues non-reentrant. If a work item is executing on a different CPU when queueing is requested, it is always queued to that CPU. This guarantees that any given work item can be executing on one CPU at maximum and if a work item is queued and executing, both are on the same CPU. The only behavior change which may affect workqueue users negatively is that non-reentrancy overrides the affinity specified by queue_work_on(). On a reentrant workqueue, the affinity specified by queue_work_on() is always followed. Now, if the work item is executing on one of the CPUs, the work item will be queued there regardless of the requested affinity. I've reviewed all workqueue users which request explicit affinity, and, fortunately, none seems to be crazy enough to exploit parallel execution of the same work item. This adds an additional busy_hash lookup if the work item was previously queued on a different CPU. This shouldn't be noticeable under any sane workload. Work item queueing isn't a very high-frequency operation and they don't jump across CPUs all the time. In a micro benchmark to exaggerate this difference - measuring the time it takes for two work items to repeatedly jump between two CPUs a number (10M) of times with busy_hash table densely populated, the difference was around 3%. While the overhead is measureable, it is only visible in pathological cases and the difference isn't huge. This change brings much needed sanity to workqueue and makes its behavior consistent with timer. I think this is the right tradeoff to make. This enables significant simplification of workqueue API. Simplification patches will follow. Signed-off-by: Tejun Heo <tj@kernel.org>
2012-08-20 21:51:23 +00:00
/*
* If @work was previously on a different pool, it might still be
* running there, in which case the work needs to be queued on that
* pool to guarantee non-reentrancy.
*/
last_pool = get_work_pool(work);
if (last_pool && last_pool != pwq->pool) {
struct worker *worker;
spin_lock(&last_pool->lock);
worker = find_worker_executing_work(last_pool, work);
if (worker && worker->current_pwq->wq == wq) {
pwq = worker->current_pwq;
workqueue: disable irq while manipulating PENDING Queueing operations use WORK_STRUCT_PENDING_BIT to synchronize access to the target work item. They first try to claim the bit and proceed with queueing only after that succeeds and there's a window between PENDING being set and the actual queueing where the task can be interrupted or preempted. There's also a similar window in process_one_work() when clearing PENDING. A work item is dequeued, gcwq->lock is released and then PENDING is cleared and the worker might get interrupted or preempted between releasing gcwq->lock and clearing PENDING. cancel[_delayed]_work_sync() tries to claim or steal PENDING. The function assumes that a work item with PENDING is either queued or in the process of being [de]queued. In the latter case, it busy-loops until either the work item loses PENDING or is queued. If canceling coincides with the above described interrupts or preemptions, the canceling task will busy-loop while the queueing or executing task is preempted. This patch keeps irq disabled across claiming PENDING and actual queueing and moves PENDING clearing in process_one_work() inside gcwq->lock so that busy looping from PENDING && !queued doesn't wait for interrupted/preempted tasks. Note that, in process_one_work(), setting last CPU and clearing PENDING got merged into single operation. This removes possible long busy-loops and will allow using try_to_grab_pending() from bh and irq contexts. v2: __queue_work() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Disable irq instead of preemption. IRQ will be disabled while grabbing gcwq->lock later anyway and this allows using try_to_grab_pending() from bh and irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:45 +00:00
} else {
/* meh... not running there, queue here */
spin_unlock(&last_pool->lock);
spin_lock(&pwq->pool->lock);
workqueue: disable irq while manipulating PENDING Queueing operations use WORK_STRUCT_PENDING_BIT to synchronize access to the target work item. They first try to claim the bit and proceed with queueing only after that succeeds and there's a window between PENDING being set and the actual queueing where the task can be interrupted or preempted. There's also a similar window in process_one_work() when clearing PENDING. A work item is dequeued, gcwq->lock is released and then PENDING is cleared and the worker might get interrupted or preempted between releasing gcwq->lock and clearing PENDING. cancel[_delayed]_work_sync() tries to claim or steal PENDING. The function assumes that a work item with PENDING is either queued or in the process of being [de]queued. In the latter case, it busy-loops until either the work item loses PENDING or is queued. If canceling coincides with the above described interrupts or preemptions, the canceling task will busy-loop while the queueing or executing task is preempted. This patch keeps irq disabled across claiming PENDING and actual queueing and moves PENDING clearing in process_one_work() inside gcwq->lock so that busy looping from PENDING && !queued doesn't wait for interrupted/preempted tasks. Note that, in process_one_work(), setting last CPU and clearing PENDING got merged into single operation. This removes possible long busy-loops and will allow using try_to_grab_pending() from bh and irq contexts. v2: __queue_work() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Disable irq instead of preemption. IRQ will be disabled while grabbing gcwq->lock later anyway and this allows using try_to_grab_pending() from bh and irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:45 +00:00
}
} else {
spin_lock(&pwq->pool->lock);
}
/*
* pwq is determined and locked. For unbound pools, we could have
* raced with pwq release and it could already be dead. If its
* refcnt is zero, repeat pwq selection. Note that pwqs never die
* without another pwq replacing it in the numa_pwq_tbl or while
* work items are executing on it, so the retrying is guaranteed to
* make forward-progress.
*/
if (unlikely(!pwq->refcnt)) {
if (wq->flags & WQ_UNBOUND) {
spin_unlock(&pwq->pool->lock);
cpu_relax();
goto retry;
}
/* oops */
WARN_ONCE(true, "workqueue: per-cpu pwq for %s on cpu%d has 0 refcnt",
wq->name, cpu);
}
/* pwq determined, queue */
trace_workqueue_queue_work(req_cpu, pwq, work);
if (WARN_ON(!list_empty(&work->entry))) {
spin_unlock(&pwq->pool->lock);
return;
}
pwq->nr_in_flight[pwq->work_color]++;
work_flags = work_color_to_flags(pwq->work_color);
if (likely(pwq->nr_active < pwq->max_active)) {
trace_workqueue_activate_work(work);
pwq->nr_active++;
worklist = &pwq->pool->worklist;
workqueue: implement lockup detector Workqueue stalls can happen from a variety of usage bugs such as missing WQ_MEM_RECLAIM flag or concurrency managed work item indefinitely staying RUNNING. These stalls can be extremely difficult to hunt down because the usual warning mechanisms can't detect workqueue stalls and the internal state is pretty opaque. To alleviate the situation, this patch implements workqueue lockup detector. It periodically monitors all worker_pools periodically and, if any pool failed to make forward progress longer than the threshold duration, triggers warning and dumps workqueue state as follows. BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 31s! Showing busy workqueues and worker pools: workqueue events: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=17/256 pending: monkey_wrench_fn, e1000_watchdog, cache_reap, vmstat_shepherd, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, cgroup_release_agent workqueue events_power_efficient: flags=0x80 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=2/256 pending: check_lifetime, neigh_periodic_work workqueue cgroup_pidlist_destroy: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/1 pending: cgroup_pidlist_destroy_work_fn ... The detection mechanism is controller through kernel parameter workqueue.watchdog_thresh and can be updated at runtime through the sysfs module parameter file. v2: Decoupled from softlockup control knobs. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Don Zickus <dzickus@redhat.com> Cc: Ulrich Obergfell <uobergfe@redhat.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Chris Mason <clm@fb.com> Cc: Andrew Morton <akpm@linux-foundation.org>
2015-12-08 16:28:04 +00:00
if (list_empty(worklist))
pwq->pool->watchdog_ts = jiffies;
} else {
work_flags |= WORK_STRUCT_DELAYED;
worklist = &pwq->delayed_works;
}
insert_work(pwq, work, worklist, work_flags);
spin_unlock(&pwq->pool->lock);
}
/**
* queue_work_on - queue work on specific cpu
* @cpu: CPU number to execute work on
* @wq: workqueue to use
* @work: work to queue
*
* We queue the work to a specific CPU, the caller must ensure it
* can't go away.
*
* Return: %false if @work was already on a queue, %true otherwise.
*/
bool queue_work_on(int cpu, struct workqueue_struct *wq,
struct work_struct *work)
{
bool ret = false;
workqueue: disable irq while manipulating PENDING Queueing operations use WORK_STRUCT_PENDING_BIT to synchronize access to the target work item. They first try to claim the bit and proceed with queueing only after that succeeds and there's a window between PENDING being set and the actual queueing where the task can be interrupted or preempted. There's also a similar window in process_one_work() when clearing PENDING. A work item is dequeued, gcwq->lock is released and then PENDING is cleared and the worker might get interrupted or preempted between releasing gcwq->lock and clearing PENDING. cancel[_delayed]_work_sync() tries to claim or steal PENDING. The function assumes that a work item with PENDING is either queued or in the process of being [de]queued. In the latter case, it busy-loops until either the work item loses PENDING or is queued. If canceling coincides with the above described interrupts or preemptions, the canceling task will busy-loop while the queueing or executing task is preempted. This patch keeps irq disabled across claiming PENDING and actual queueing and moves PENDING clearing in process_one_work() inside gcwq->lock so that busy looping from PENDING && !queued doesn't wait for interrupted/preempted tasks. Note that, in process_one_work(), setting last CPU and clearing PENDING got merged into single operation. This removes possible long busy-loops and will allow using try_to_grab_pending() from bh and irq contexts. v2: __queue_work() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Disable irq instead of preemption. IRQ will be disabled while grabbing gcwq->lock later anyway and this allows using try_to_grab_pending() from bh and irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:45 +00:00
unsigned long flags;
workqueue: disable irq while manipulating PENDING Queueing operations use WORK_STRUCT_PENDING_BIT to synchronize access to the target work item. They first try to claim the bit and proceed with queueing only after that succeeds and there's a window between PENDING being set and the actual queueing where the task can be interrupted or preempted. There's also a similar window in process_one_work() when clearing PENDING. A work item is dequeued, gcwq->lock is released and then PENDING is cleared and the worker might get interrupted or preempted between releasing gcwq->lock and clearing PENDING. cancel[_delayed]_work_sync() tries to claim or steal PENDING. The function assumes that a work item with PENDING is either queued or in the process of being [de]queued. In the latter case, it busy-loops until either the work item loses PENDING or is queued. If canceling coincides with the above described interrupts or preemptions, the canceling task will busy-loop while the queueing or executing task is preempted. This patch keeps irq disabled across claiming PENDING and actual queueing and moves PENDING clearing in process_one_work() inside gcwq->lock so that busy looping from PENDING && !queued doesn't wait for interrupted/preempted tasks. Note that, in process_one_work(), setting last CPU and clearing PENDING got merged into single operation. This removes possible long busy-loops and will allow using try_to_grab_pending() from bh and irq contexts. v2: __queue_work() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Disable irq instead of preemption. IRQ will be disabled while grabbing gcwq->lock later anyway and this allows using try_to_grab_pending() from bh and irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:45 +00:00
local_irq_save(flags);
if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
__queue_work(cpu, wq, work);
ret = true;
}
workqueue: disable irq while manipulating PENDING Queueing operations use WORK_STRUCT_PENDING_BIT to synchronize access to the target work item. They first try to claim the bit and proceed with queueing only after that succeeds and there's a window between PENDING being set and the actual queueing where the task can be interrupted or preempted. There's also a similar window in process_one_work() when clearing PENDING. A work item is dequeued, gcwq->lock is released and then PENDING is cleared and the worker might get interrupted or preempted between releasing gcwq->lock and clearing PENDING. cancel[_delayed]_work_sync() tries to claim or steal PENDING. The function assumes that a work item with PENDING is either queued or in the process of being [de]queued. In the latter case, it busy-loops until either the work item loses PENDING or is queued. If canceling coincides with the above described interrupts or preemptions, the canceling task will busy-loop while the queueing or executing task is preempted. This patch keeps irq disabled across claiming PENDING and actual queueing and moves PENDING clearing in process_one_work() inside gcwq->lock so that busy looping from PENDING && !queued doesn't wait for interrupted/preempted tasks. Note that, in process_one_work(), setting last CPU and clearing PENDING got merged into single operation. This removes possible long busy-loops and will allow using try_to_grab_pending() from bh and irq contexts. v2: __queue_work() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Disable irq instead of preemption. IRQ will be disabled while grabbing gcwq->lock later anyway and this allows using try_to_grab_pending() from bh and irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:45 +00:00
local_irq_restore(flags);
return ret;
}
EXPORT_SYMBOL(queue_work_on);
void delayed_work_timer_fn(unsigned long __data)
{
struct delayed_work *dwork = (struct delayed_work *)__data;
/* should have been called from irqsafe timer with irq already off */
workqueue: add delayed_work->wq to simplify reentrancy handling To avoid executing the same work item from multiple CPUs concurrently, a work_struct records the last pool it was on in its ->data so that, on the next queueing, the pool can be queried to determine whether the work item is still executing or not. A delayed_work goes through timer before actually being queued on the target workqueue and the timer needs to know the target workqueue and CPU. This is currently achieved by modifying delayed_work->work.data such that it points to the cwq which points to the target workqueue and the last CPU the work item was on. __queue_delayed_work() extracts the last CPU from delayed_work->work.data and then combines it with the target workqueue to create new work.data. The only thing this rather ugly hack achieves is encoding the target workqueue into delayed_work->work.data without using a separate field, which could be a trade off one can make; unfortunately, this entangles work->data management between regular workqueue and delayed_work code by setting cwq pointer before the work item is actually queued and becomes a hindrance for further improvements of work->data handling. This can be easily made sane by adding a target workqueue field to delayed_work. While delayed_work is used widely in the kernel and this does make it a bit larger (<5%), I think this is the right trade-off especially given the prospect of much saner handling of work->data which currently involves quite tricky memory barrier dancing, and don't expect to see any measureable effect. Add delayed_work->wq and drop the delayed_work->work.data overloading. tj: Rewrote the description. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2013-02-07 02:04:53 +00:00
__queue_work(dwork->cpu, dwork->wq, &dwork->work);
}
EXPORT_SYMBOL(delayed_work_timer_fn);
static void __queue_delayed_work(int cpu, struct workqueue_struct *wq,
struct delayed_work *dwork, unsigned long delay)
{
struct timer_list *timer = &dwork->timer;
struct work_struct *work = &dwork->work;
WARN_ON_ONCE(timer->function != delayed_work_timer_fn ||
timer->data != (unsigned long)dwork);
WARN_ON_ONCE(timer_pending(timer));
WARN_ON_ONCE(!list_empty(&work->entry));
workqueue: mod_delayed_work_on() shouldn't queue timer on 0 delay 8376fe22c7 ("workqueue: implement mod_delayed_work[_on]()") implemented mod_delayed_work[_on]() using the improved try_to_grab_pending(). The function is later used, among others, to replace [__]candel_delayed_work() + queue_delayed_work() combinations. Unfortunately, a delayed_work item w/ zero @delay is handled slightly differently by mod_delayed_work_on() compared to queue_delayed_work_on(). The latter skips timer altogether and directly queues it using queue_work_on() while the former schedules timer which will expire on the closest tick. This means, when @delay is zero, that [__]cancel_delayed_work() + queue_delayed_work_on() makes the target item immediately executable while mod_delayed_work_on() may induce delay of upto a full tick. This somewhat subtle difference breaks some of the converted users. e.g. block queue plugging uses delayed_work for deferred processing and uses mod_delayed_work_on() when the queue needs to be immediately unplugged. The above problem manifested as noticeably higher number of context switches under certain circumstances. The difference in behavior was caused by missing special case handling for 0 delay in mod_delayed_work_on() compared to queue_delayed_work_on(). Joonsoo Kim posted a patch to add it - ("workqueue: optimize mod_delayed_work_on() when @delay == 0")[1]. The patch was queued for 3.8 but it was described as optimization and I missed that it was a correctness issue. As both queue_delayed_work_on() and mod_delayed_work_on() use __queue_delayed_work() for queueing, it seems that the better approach is to move the 0 delay special handling to the function instead of duplicating it in mod_delayed_work_on(). Fix the problem by moving 0 delay special case handling from queue_delayed_work_on() to __queue_delayed_work(). This replaces Joonsoo's patch. [1] http://thread.gmane.org/gmane.linux.kernel/1379011/focus=1379012 Signed-off-by: Tejun Heo <tj@kernel.org> Reported-and-tested-by: Anders Kaseorg <andersk@MIT.EDU> Reported-and-tested-by: Zlatko Calusic <zlatko.calusic@iskon.hr> LKML-Reference: <alpine.DEB.2.00.1211280953350.26602@dr-wily.mit.edu> LKML-Reference: <50A78AA9.5040904@iskon.hr> Cc: Joonsoo Kim <js1304@gmail.com>
2012-12-02 00:23:42 +00:00
/*
* If @delay is 0, queue @dwork->work immediately. This is for
* both optimization and correctness. The earliest @timer can
* expire is on the closest next tick and delayed_work users depend
* on that there's no such delay when @delay is 0.
*/
if (!delay) {
__queue_work(cpu, wq, &dwork->work);
return;
}
timer_stats_timer_set_start_info(&dwork->timer);
workqueue: add delayed_work->wq to simplify reentrancy handling To avoid executing the same work item from multiple CPUs concurrently, a work_struct records the last pool it was on in its ->data so that, on the next queueing, the pool can be queried to determine whether the work item is still executing or not. A delayed_work goes through timer before actually being queued on the target workqueue and the timer needs to know the target workqueue and CPU. This is currently achieved by modifying delayed_work->work.data such that it points to the cwq which points to the target workqueue and the last CPU the work item was on. __queue_delayed_work() extracts the last CPU from delayed_work->work.data and then combines it with the target workqueue to create new work.data. The only thing this rather ugly hack achieves is encoding the target workqueue into delayed_work->work.data without using a separate field, which could be a trade off one can make; unfortunately, this entangles work->data management between regular workqueue and delayed_work code by setting cwq pointer before the work item is actually queued and becomes a hindrance for further improvements of work->data handling. This can be easily made sane by adding a target workqueue field to delayed_work. While delayed_work is used widely in the kernel and this does make it a bit larger (<5%), I think this is the right trade-off especially given the prospect of much saner handling of work->data which currently involves quite tricky memory barrier dancing, and don't expect to see any measureable effect. Add delayed_work->wq and drop the delayed_work->work.data overloading. tj: Rewrote the description. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2013-02-07 02:04:53 +00:00
dwork->wq = wq;
dwork->cpu = cpu;
timer->expires = jiffies + delay;
Revert "workqueue: make sure delayed work run in local cpu" This reverts commit 874bbfe600a660cba9c776b3957b1ce393151b76. Workqueue used to implicity guarantee that work items queued without explicit CPU specified are put on the local CPU. Recent changes in timer broke the guarantee and led to vmstat breakage which was fixed by 176bed1de5bf ("vmstat: explicitly schedule per-cpu work on the CPU we need it to run on"). vmstat is the most likely to expose the issue and it's quite possible that there are other similar problems which are a lot more difficult to trigger. As a preventive measure, 874bbfe600a6 ("workqueue: make sure delayed work run in local cpu") was applied to restore the local CPU guarnatee. Unfortunately, the change exposed a bug in timer code which got fixed by 22b886dd1018 ("timers: Use proper base migration in add_timer_on()"). Due to code restructuring, the commit couldn't be backported beyond certain point and stable kernels which only had 874bbfe600a6 started crashing. The local CPU guarantee was accidental more than anything else and we want to get rid of it anyway. As, with the vmstat case fixed, 874bbfe600a6 is causing more problems than it's fixing, it has been decided to take the chance and officially break the guarantee by reverting the commit. A debug feature will be added to force foreign CPU assignment to expose cases relying on the guarantee and fixes for the individual cases will be backported to stable as necessary. Signed-off-by: Tejun Heo <tj@kernel.org> Fixes: 874bbfe600a6 ("workqueue: make sure delayed work run in local cpu") Link: http://lkml.kernel.org/g/20160120211926.GJ10810@quack.suse.cz Cc: stable@vger.kernel.org Cc: Mike Galbraith <umgwanakikbuti@gmail.com> Cc: Henrique de Moraes Holschuh <hmh@hmh.eng.br> Cc: Daniel Bilik <daniel.bilik@neosystem.cz> Cc: Jan Kara <jack@suse.cz> Cc: Shaohua Li <shli@fb.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Ben Hutchings <ben@decadent.org.uk> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Daniel Bilik <daniel.bilik@neosystem.cz> Cc: Jiri Slaby <jslaby@suse.cz> Cc: Michal Hocko <mhocko@kernel.org>
2016-02-09 21:11:26 +00:00
if (unlikely(cpu != WORK_CPU_UNBOUND))
add_timer_on(timer, cpu);
else
add_timer(timer);
}
/**
* queue_delayed_work_on - queue work on specific CPU after delay
* @cpu: CPU number to execute work on
* @wq: workqueue to use
* @dwork: work to queue
* @delay: number of jiffies to wait before queueing
*
* Return: %false if @work was already on a queue, %true otherwise. If
* @delay is zero and @dwork is idle, it will be scheduled for immediate
* execution.
*/
bool queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
struct delayed_work *dwork, unsigned long delay)
{
struct work_struct *work = &dwork->work;
bool ret = false;
workqueue: disable irq while manipulating PENDING Queueing operations use WORK_STRUCT_PENDING_BIT to synchronize access to the target work item. They first try to claim the bit and proceed with queueing only after that succeeds and there's a window between PENDING being set and the actual queueing where the task can be interrupted or preempted. There's also a similar window in process_one_work() when clearing PENDING. A work item is dequeued, gcwq->lock is released and then PENDING is cleared and the worker might get interrupted or preempted between releasing gcwq->lock and clearing PENDING. cancel[_delayed]_work_sync() tries to claim or steal PENDING. The function assumes that a work item with PENDING is either queued or in the process of being [de]queued. In the latter case, it busy-loops until either the work item loses PENDING or is queued. If canceling coincides with the above described interrupts or preemptions, the canceling task will busy-loop while the queueing or executing task is preempted. This patch keeps irq disabled across claiming PENDING and actual queueing and moves PENDING clearing in process_one_work() inside gcwq->lock so that busy looping from PENDING && !queued doesn't wait for interrupted/preempted tasks. Note that, in process_one_work(), setting last CPU and clearing PENDING got merged into single operation. This removes possible long busy-loops and will allow using try_to_grab_pending() from bh and irq contexts. v2: __queue_work() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Disable irq instead of preemption. IRQ will be disabled while grabbing gcwq->lock later anyway and this allows using try_to_grab_pending() from bh and irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:45 +00:00
unsigned long flags;
workqueue: disable irq while manipulating PENDING Queueing operations use WORK_STRUCT_PENDING_BIT to synchronize access to the target work item. They first try to claim the bit and proceed with queueing only after that succeeds and there's a window between PENDING being set and the actual queueing where the task can be interrupted or preempted. There's also a similar window in process_one_work() when clearing PENDING. A work item is dequeued, gcwq->lock is released and then PENDING is cleared and the worker might get interrupted or preempted between releasing gcwq->lock and clearing PENDING. cancel[_delayed]_work_sync() tries to claim or steal PENDING. The function assumes that a work item with PENDING is either queued or in the process of being [de]queued. In the latter case, it busy-loops until either the work item loses PENDING or is queued. If canceling coincides with the above described interrupts or preemptions, the canceling task will busy-loop while the queueing or executing task is preempted. This patch keeps irq disabled across claiming PENDING and actual queueing and moves PENDING clearing in process_one_work() inside gcwq->lock so that busy looping from PENDING && !queued doesn't wait for interrupted/preempted tasks. Note that, in process_one_work(), setting last CPU and clearing PENDING got merged into single operation. This removes possible long busy-loops and will allow using try_to_grab_pending() from bh and irq contexts. v2: __queue_work() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Disable irq instead of preemption. IRQ will be disabled while grabbing gcwq->lock later anyway and this allows using try_to_grab_pending() from bh and irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:45 +00:00
/* read the comment in __queue_work() */
local_irq_save(flags);
if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
__queue_delayed_work(cpu, wq, dwork, delay);
ret = true;
}
workqueue: disable irq while manipulating PENDING Queueing operations use WORK_STRUCT_PENDING_BIT to synchronize access to the target work item. They first try to claim the bit and proceed with queueing only after that succeeds and there's a window between PENDING being set and the actual queueing where the task can be interrupted or preempted. There's also a similar window in process_one_work() when clearing PENDING. A work item is dequeued, gcwq->lock is released and then PENDING is cleared and the worker might get interrupted or preempted between releasing gcwq->lock and clearing PENDING. cancel[_delayed]_work_sync() tries to claim or steal PENDING. The function assumes that a work item with PENDING is either queued or in the process of being [de]queued. In the latter case, it busy-loops until either the work item loses PENDING or is queued. If canceling coincides with the above described interrupts or preemptions, the canceling task will busy-loop while the queueing or executing task is preempted. This patch keeps irq disabled across claiming PENDING and actual queueing and moves PENDING clearing in process_one_work() inside gcwq->lock so that busy looping from PENDING && !queued doesn't wait for interrupted/preempted tasks. Note that, in process_one_work(), setting last CPU and clearing PENDING got merged into single operation. This removes possible long busy-loops and will allow using try_to_grab_pending() from bh and irq contexts. v2: __queue_work() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Disable irq instead of preemption. IRQ will be disabled while grabbing gcwq->lock later anyway and this allows using try_to_grab_pending() from bh and irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:45 +00:00
local_irq_restore(flags);
return ret;
}
EXPORT_SYMBOL(queue_delayed_work_on);
/**
* mod_delayed_work_on - modify delay of or queue a delayed work on specific CPU
* @cpu: CPU number to execute work on
* @wq: workqueue to use
* @dwork: work to queue
* @delay: number of jiffies to wait before queueing
*
* If @dwork is idle, equivalent to queue_delayed_work_on(); otherwise,
* modify @dwork's timer so that it expires after @delay. If @delay is
* zero, @work is guaranteed to be scheduled immediately regardless of its
* current state.
*
* Return: %false if @dwork was idle and queued, %true if @dwork was
* pending and its timer was modified.
*
* This function is safe to call from any context including IRQ handler.
* See try_to_grab_pending() for details.
*/
bool mod_delayed_work_on(int cpu, struct workqueue_struct *wq,
struct delayed_work *dwork, unsigned long delay)
{
unsigned long flags;
int ret;
do {
ret = try_to_grab_pending(&dwork->work, true, &flags);
} while (unlikely(ret == -EAGAIN));
if (likely(ret >= 0)) {
__queue_delayed_work(cpu, wq, dwork, delay);
local_irq_restore(flags);
}
/* -ENOENT from try_to_grab_pending() becomes %true */
return ret;
}
EXPORT_SYMBOL_GPL(mod_delayed_work_on);
/**
* worker_enter_idle - enter idle state
* @worker: worker which is entering idle state
*
* @worker is entering idle state. Update stats and idle timer if
* necessary.
*
* LOCKING:
* spin_lock_irq(pool->lock).
*/
static void worker_enter_idle(struct worker *worker)
{
struct worker_pool *pool = worker->pool;
if (WARN_ON_ONCE(worker->flags & WORKER_IDLE) ||
WARN_ON_ONCE(!list_empty(&worker->entry) &&
(worker->hentry.next || worker->hentry.pprev)))
return;
/* can't use worker_set_flags(), also called from create_worker() */
worker->flags |= WORKER_IDLE;
pool->nr_idle++;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
worker->last_active = jiffies;
/* idle_list is LIFO */
list_add(&worker->entry, &pool->idle_list);
if (too_many_workers(pool) && !timer_pending(&pool->idle_timer))
mod_timer(&pool->idle_timer, jiffies + IDLE_WORKER_TIMEOUT);
/*
* Sanity check nr_running. Because wq_unbind_fn() releases
* pool->lock between setting %WORKER_UNBOUND and zapping
* nr_running, the warning may trigger spuriously. Check iff
* unbind is not in progress.
*/
WARN_ON_ONCE(!(pool->flags & POOL_DISASSOCIATED) &&
pool->nr_workers == pool->nr_idle &&
atomic_read(&pool->nr_running));
}
/**
* worker_leave_idle - leave idle state
* @worker: worker which is leaving idle state
*
* @worker is leaving idle state. Update stats.
*
* LOCKING:
* spin_lock_irq(pool->lock).
*/
static void worker_leave_idle(struct worker *worker)
{
struct worker_pool *pool = worker->pool;
if (WARN_ON_ONCE(!(worker->flags & WORKER_IDLE)))
return;
worker_clr_flags(worker, WORKER_IDLE);
pool->nr_idle--;
list_del_init(&worker->entry);
}
static struct worker *alloc_worker(int node)
{
struct worker *worker;
worker = kzalloc_node(sizeof(*worker), GFP_KERNEL, node);
if (worker) {
INIT_LIST_HEAD(&worker->entry);
INIT_LIST_HEAD(&worker->scheduled);
INIT_LIST_HEAD(&worker->node);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
/* on creation a worker is in !idle && prep state */
worker->flags = WORKER_PREP;
}
return worker;
}
/**
* worker_attach_to_pool() - attach a worker to a pool
* @worker: worker to be attached
* @pool: the target pool
*
* Attach @worker to @pool. Once attached, the %WORKER_UNBOUND flag and
* cpu-binding of @worker are kept coordinated with the pool across
* cpu-[un]hotplugs.
*/
static void worker_attach_to_pool(struct worker *worker,
struct worker_pool *pool)
{
mutex_lock(&pool->attach_mutex);
/*
* set_cpus_allowed_ptr() will fail if the cpumask doesn't have any
* online CPUs. It'll be re-applied when any of the CPUs come up.
*/
set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);
/*
* The pool->attach_mutex ensures %POOL_DISASSOCIATED remains
* stable across this function. See the comments above the
* flag definition for details.
*/
if (pool->flags & POOL_DISASSOCIATED)
worker->flags |= WORKER_UNBOUND;
list_add_tail(&worker->node, &pool->workers);
mutex_unlock(&pool->attach_mutex);
}
workqueue: async worker destruction worker destruction includes these parts of code: adjust pool's stats remove the worker from idle list detach the worker from the pool kthread_stop() to wait for the worker's task exit free the worker struct We can find out that there is no essential work to do after kthread_stop(), which means destroy_worker() doesn't need to wait for the worker's task exit, so we can remove kthread_stop() and free the worker struct in the worker exiting path. However, put_unbound_pool() still needs to sync the all the workers' destruction before destroying the pool; otherwise, the workers may access to the invalid pool when they are exiting. So we also move the code of "detach the worker" to the exiting path and let put_unbound_pool() to sync with this code via detach_completion. The code of "detach the worker" is wrapped in a new function "worker_detach_from_pool()" although worker_detach_from_pool() is only called once (in worker_thread()) after this patch, but we need to wrap it for these reasons: 1) The code of "detach the worker" is not short enough to unfold them in worker_thread(). 2) the name of "worker_detach_from_pool()" is self-comment, and we add some comments above the function. 3) it will be shared by rescuer in later patch which allows rescuer and normal thread use the same attach/detach frameworks. The worker id is freed when detaching which happens before the worker is fully dead, but this id of the dying worker may be re-used for a new worker, so the dying worker's task name is changed to "worker/dying" to avoid two or several workers having the same name. Since "detach the worker" is moved out from destroy_worker(), destroy_worker() doesn't require manager_mutex, so the "lockdep_assert_held(&pool->manager_mutex)" in destroy_worker() is removed, and destroy_worker() is not protected by manager_mutex in put_unbound_pool(). tj: Minor description updates. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2014-05-20 09:46:29 +00:00
/**
* worker_detach_from_pool() - detach a worker from its pool
* @worker: worker which is attached to its pool
* @pool: the pool @worker is attached to
*
* Undo the attaching which had been done in worker_attach_to_pool(). The
* caller worker shouldn't access to the pool after detached except it has
* other reference to the pool.
workqueue: async worker destruction worker destruction includes these parts of code: adjust pool's stats remove the worker from idle list detach the worker from the pool kthread_stop() to wait for the worker's task exit free the worker struct We can find out that there is no essential work to do after kthread_stop(), which means destroy_worker() doesn't need to wait for the worker's task exit, so we can remove kthread_stop() and free the worker struct in the worker exiting path. However, put_unbound_pool() still needs to sync the all the workers' destruction before destroying the pool; otherwise, the workers may access to the invalid pool when they are exiting. So we also move the code of "detach the worker" to the exiting path and let put_unbound_pool() to sync with this code via detach_completion. The code of "detach the worker" is wrapped in a new function "worker_detach_from_pool()" although worker_detach_from_pool() is only called once (in worker_thread()) after this patch, but we need to wrap it for these reasons: 1) The code of "detach the worker" is not short enough to unfold them in worker_thread(). 2) the name of "worker_detach_from_pool()" is self-comment, and we add some comments above the function. 3) it will be shared by rescuer in later patch which allows rescuer and normal thread use the same attach/detach frameworks. The worker id is freed when detaching which happens before the worker is fully dead, but this id of the dying worker may be re-used for a new worker, so the dying worker's task name is changed to "worker/dying" to avoid two or several workers having the same name. Since "detach the worker" is moved out from destroy_worker(), destroy_worker() doesn't require manager_mutex, so the "lockdep_assert_held(&pool->manager_mutex)" in destroy_worker() is removed, and destroy_worker() is not protected by manager_mutex in put_unbound_pool(). tj: Minor description updates. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2014-05-20 09:46:29 +00:00
*/
static void worker_detach_from_pool(struct worker *worker,
struct worker_pool *pool)
{
struct completion *detach_completion = NULL;
mutex_lock(&pool->attach_mutex);
list_del(&worker->node);
if (list_empty(&pool->workers))
workqueue: async worker destruction worker destruction includes these parts of code: adjust pool's stats remove the worker from idle list detach the worker from the pool kthread_stop() to wait for the worker's task exit free the worker struct We can find out that there is no essential work to do after kthread_stop(), which means destroy_worker() doesn't need to wait for the worker's task exit, so we can remove kthread_stop() and free the worker struct in the worker exiting path. However, put_unbound_pool() still needs to sync the all the workers' destruction before destroying the pool; otherwise, the workers may access to the invalid pool when they are exiting. So we also move the code of "detach the worker" to the exiting path and let put_unbound_pool() to sync with this code via detach_completion. The code of "detach the worker" is wrapped in a new function "worker_detach_from_pool()" although worker_detach_from_pool() is only called once (in worker_thread()) after this patch, but we need to wrap it for these reasons: 1) The code of "detach the worker" is not short enough to unfold them in worker_thread(). 2) the name of "worker_detach_from_pool()" is self-comment, and we add some comments above the function. 3) it will be shared by rescuer in later patch which allows rescuer and normal thread use the same attach/detach frameworks. The worker id is freed when detaching which happens before the worker is fully dead, but this id of the dying worker may be re-used for a new worker, so the dying worker's task name is changed to "worker/dying" to avoid two or several workers having the same name. Since "detach the worker" is moved out from destroy_worker(), destroy_worker() doesn't require manager_mutex, so the "lockdep_assert_held(&pool->manager_mutex)" in destroy_worker() is removed, and destroy_worker() is not protected by manager_mutex in put_unbound_pool(). tj: Minor description updates. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2014-05-20 09:46:29 +00:00
detach_completion = pool->detach_completion;
mutex_unlock(&pool->attach_mutex);
workqueue: async worker destruction worker destruction includes these parts of code: adjust pool's stats remove the worker from idle list detach the worker from the pool kthread_stop() to wait for the worker's task exit free the worker struct We can find out that there is no essential work to do after kthread_stop(), which means destroy_worker() doesn't need to wait for the worker's task exit, so we can remove kthread_stop() and free the worker struct in the worker exiting path. However, put_unbound_pool() still needs to sync the all the workers' destruction before destroying the pool; otherwise, the workers may access to the invalid pool when they are exiting. So we also move the code of "detach the worker" to the exiting path and let put_unbound_pool() to sync with this code via detach_completion. The code of "detach the worker" is wrapped in a new function "worker_detach_from_pool()" although worker_detach_from_pool() is only called once (in worker_thread()) after this patch, but we need to wrap it for these reasons: 1) The code of "detach the worker" is not short enough to unfold them in worker_thread(). 2) the name of "worker_detach_from_pool()" is self-comment, and we add some comments above the function. 3) it will be shared by rescuer in later patch which allows rescuer and normal thread use the same attach/detach frameworks. The worker id is freed when detaching which happens before the worker is fully dead, but this id of the dying worker may be re-used for a new worker, so the dying worker's task name is changed to "worker/dying" to avoid two or several workers having the same name. Since "detach the worker" is moved out from destroy_worker(), destroy_worker() doesn't require manager_mutex, so the "lockdep_assert_held(&pool->manager_mutex)" in destroy_worker() is removed, and destroy_worker() is not protected by manager_mutex in put_unbound_pool(). tj: Minor description updates. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2014-05-20 09:46:29 +00:00
/* clear leftover flags without pool->lock after it is detached */
worker->flags &= ~(WORKER_UNBOUND | WORKER_REBOUND);
workqueue: async worker destruction worker destruction includes these parts of code: adjust pool's stats remove the worker from idle list detach the worker from the pool kthread_stop() to wait for the worker's task exit free the worker struct We can find out that there is no essential work to do after kthread_stop(), which means destroy_worker() doesn't need to wait for the worker's task exit, so we can remove kthread_stop() and free the worker struct in the worker exiting path. However, put_unbound_pool() still needs to sync the all the workers' destruction before destroying the pool; otherwise, the workers may access to the invalid pool when they are exiting. So we also move the code of "detach the worker" to the exiting path and let put_unbound_pool() to sync with this code via detach_completion. The code of "detach the worker" is wrapped in a new function "worker_detach_from_pool()" although worker_detach_from_pool() is only called once (in worker_thread()) after this patch, but we need to wrap it for these reasons: 1) The code of "detach the worker" is not short enough to unfold them in worker_thread(). 2) the name of "worker_detach_from_pool()" is self-comment, and we add some comments above the function. 3) it will be shared by rescuer in later patch which allows rescuer and normal thread use the same attach/detach frameworks. The worker id is freed when detaching which happens before the worker is fully dead, but this id of the dying worker may be re-used for a new worker, so the dying worker's task name is changed to "worker/dying" to avoid two or several workers having the same name. Since "detach the worker" is moved out from destroy_worker(), destroy_worker() doesn't require manager_mutex, so the "lockdep_assert_held(&pool->manager_mutex)" in destroy_worker() is removed, and destroy_worker() is not protected by manager_mutex in put_unbound_pool(). tj: Minor description updates. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2014-05-20 09:46:29 +00:00
if (detach_completion)
complete(detach_completion);
}
/**
* create_worker - create a new workqueue worker
* @pool: pool the new worker will belong to
*
* Create and start a new worker which is attached to @pool.
*
* CONTEXT:
* Might sleep. Does GFP_KERNEL allocations.
*
* Return:
* Pointer to the newly created worker.
*/
2012-07-17 19:39:27 +00:00
static struct worker *create_worker(struct worker_pool *pool)
{
struct worker *worker = NULL;
int id = -1;
char id_buf[16];
/* ID is needed to determine kthread name */
id = ida_simple_get(&pool->worker_ida, 0, 0, GFP_KERNEL);
if (id < 0)
goto fail;
worker = alloc_worker(pool->node);
if (!worker)
goto fail;
worker->pool = pool;
worker->id = id;
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
if (pool->cpu >= 0)
snprintf(id_buf, sizeof(id_buf), "%d:%d%s", pool->cpu, id,
pool->attrs->nice < 0 ? "H" : "");
else
snprintf(id_buf, sizeof(id_buf), "u%d:%d", pool->id, id);
worker->task = kthread_create_on_node(worker_thread, worker, pool->node,
"kworker/%s", id_buf);
if (IS_ERR(worker->task))
goto fail;
set_user_nice(worker->task, pool->attrs->nice);
kthread_bind_mask(worker->task, pool->attrs->cpumask);
/* successful, attach the worker to the pool */
worker_attach_to_pool(worker, pool);
/* start the newly created worker */
spin_lock_irq(&pool->lock);
worker->pool->nr_workers++;
worker_enter_idle(worker);
wake_up_process(worker->task);
spin_unlock_irq(&pool->lock);
return worker;
fail:
if (id >= 0)
ida_simple_remove(&pool->worker_ida, id);
kfree(worker);
return NULL;
}
/**
* destroy_worker - destroy a workqueue worker
* @worker: worker to be destroyed
*
workqueue: destroy_worker() should destroy idle workers only We used to have the CPU online failure path where a worker is created and then destroyed without being started. A worker was created for the CPU coming online and if the online operation failed the created worker was shut down without being started. But this behavior was changed. The first worker is created and started at the same time for the CPU coming online. It means that we had already ensured in the code that destroy_worker() destroys only idle workers and we don't want to allow it to destroy any non-idle worker in the future. Otherwise, it may be buggy and it may be extremely hard to check. We should force destroy_worker() to destroy only idle workers explicitly. Since destroy_worker() destroys only idle workers, this patch does not change any functionality. We just need to update the comments and the sanity check code. In the sanity check code, we will refuse to destroy the worker if !(worker->flags & WORKER_IDLE). If the worker entered idle which means it is already started, so we remove the check of "worker->flags & WORKER_STARTED", after this removal, WORKER_STARTED is totally unneeded, so we remove WORKER_STARTED too. In the comments for create_worker(), "Create a new worker which is bound..." is changed to "... which is attached..." due to we change the name of this behavior to attaching. tj: Minor description / comment updates. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2014-05-20 09:46:28 +00:00
* Destroy @worker and adjust @pool stats accordingly. The worker should
* be idle.
*
* CONTEXT:
workqueue: async worker destruction worker destruction includes these parts of code: adjust pool's stats remove the worker from idle list detach the worker from the pool kthread_stop() to wait for the worker's task exit free the worker struct We can find out that there is no essential work to do after kthread_stop(), which means destroy_worker() doesn't need to wait for the worker's task exit, so we can remove kthread_stop() and free the worker struct in the worker exiting path. However, put_unbound_pool() still needs to sync the all the workers' destruction before destroying the pool; otherwise, the workers may access to the invalid pool when they are exiting. So we also move the code of "detach the worker" to the exiting path and let put_unbound_pool() to sync with this code via detach_completion. The code of "detach the worker" is wrapped in a new function "worker_detach_from_pool()" although worker_detach_from_pool() is only called once (in worker_thread()) after this patch, but we need to wrap it for these reasons: 1) The code of "detach the worker" is not short enough to unfold them in worker_thread(). 2) the name of "worker_detach_from_pool()" is self-comment, and we add some comments above the function. 3) it will be shared by rescuer in later patch which allows rescuer and normal thread use the same attach/detach frameworks. The worker id is freed when detaching which happens before the worker is fully dead, but this id of the dying worker may be re-used for a new worker, so the dying worker's task name is changed to "worker/dying" to avoid two or several workers having the same name. Since "detach the worker" is moved out from destroy_worker(), destroy_worker() doesn't require manager_mutex, so the "lockdep_assert_held(&pool->manager_mutex)" in destroy_worker() is removed, and destroy_worker() is not protected by manager_mutex in put_unbound_pool(). tj: Minor description updates. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2014-05-20 09:46:29 +00:00
* spin_lock_irq(pool->lock).
*/
static void destroy_worker(struct worker *worker)
{
struct worker_pool *pool = worker->pool;
lockdep_assert_held(&pool->lock);
/* sanity check frenzy */
if (WARN_ON(worker->current_work) ||
workqueue: destroy_worker() should destroy idle workers only We used to have the CPU online failure path where a worker is created and then destroyed without being started. A worker was created for the CPU coming online and if the online operation failed the created worker was shut down without being started. But this behavior was changed. The first worker is created and started at the same time for the CPU coming online. It means that we had already ensured in the code that destroy_worker() destroys only idle workers and we don't want to allow it to destroy any non-idle worker in the future. Otherwise, it may be buggy and it may be extremely hard to check. We should force destroy_worker() to destroy only idle workers explicitly. Since destroy_worker() destroys only idle workers, this patch does not change any functionality. We just need to update the comments and the sanity check code. In the sanity check code, we will refuse to destroy the worker if !(worker->flags & WORKER_IDLE). If the worker entered idle which means it is already started, so we remove the check of "worker->flags & WORKER_STARTED", after this removal, WORKER_STARTED is totally unneeded, so we remove WORKER_STARTED too. In the comments for create_worker(), "Create a new worker which is bound..." is changed to "... which is attached..." due to we change the name of this behavior to attaching. tj: Minor description / comment updates. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2014-05-20 09:46:28 +00:00
WARN_ON(!list_empty(&worker->scheduled)) ||
WARN_ON(!(worker->flags & WORKER_IDLE)))
return;
workqueue: destroy_worker() should destroy idle workers only We used to have the CPU online failure path where a worker is created and then destroyed without being started. A worker was created for the CPU coming online and if the online operation failed the created worker was shut down without being started. But this behavior was changed. The first worker is created and started at the same time for the CPU coming online. It means that we had already ensured in the code that destroy_worker() destroys only idle workers and we don't want to allow it to destroy any non-idle worker in the future. Otherwise, it may be buggy and it may be extremely hard to check. We should force destroy_worker() to destroy only idle workers explicitly. Since destroy_worker() destroys only idle workers, this patch does not change any functionality. We just need to update the comments and the sanity check code. In the sanity check code, we will refuse to destroy the worker if !(worker->flags & WORKER_IDLE). If the worker entered idle which means it is already started, so we remove the check of "worker->flags & WORKER_STARTED", after this removal, WORKER_STARTED is totally unneeded, so we remove WORKER_STARTED too. In the comments for create_worker(), "Create a new worker which is bound..." is changed to "... which is attached..." due to we change the name of this behavior to attaching. tj: Minor description / comment updates. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2014-05-20 09:46:28 +00:00
pool->nr_workers--;
pool->nr_idle--;
list_del_init(&worker->entry);
worker->flags |= WORKER_DIE;
workqueue: async worker destruction worker destruction includes these parts of code: adjust pool's stats remove the worker from idle list detach the worker from the pool kthread_stop() to wait for the worker's task exit free the worker struct We can find out that there is no essential work to do after kthread_stop(), which means destroy_worker() doesn't need to wait for the worker's task exit, so we can remove kthread_stop() and free the worker struct in the worker exiting path. However, put_unbound_pool() still needs to sync the all the workers' destruction before destroying the pool; otherwise, the workers may access to the invalid pool when they are exiting. So we also move the code of "detach the worker" to the exiting path and let put_unbound_pool() to sync with this code via detach_completion. The code of "detach the worker" is wrapped in a new function "worker_detach_from_pool()" although worker_detach_from_pool() is only called once (in worker_thread()) after this patch, but we need to wrap it for these reasons: 1) The code of "detach the worker" is not short enough to unfold them in worker_thread(). 2) the name of "worker_detach_from_pool()" is self-comment, and we add some comments above the function. 3) it will be shared by rescuer in later patch which allows rescuer and normal thread use the same attach/detach frameworks. The worker id is freed when detaching which happens before the worker is fully dead, but this id of the dying worker may be re-used for a new worker, so the dying worker's task name is changed to "worker/dying" to avoid two or several workers having the same name. Since "detach the worker" is moved out from destroy_worker(), destroy_worker() doesn't require manager_mutex, so the "lockdep_assert_held(&pool->manager_mutex)" in destroy_worker() is removed, and destroy_worker() is not protected by manager_mutex in put_unbound_pool(). tj: Minor description updates. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2014-05-20 09:46:29 +00:00
wake_up_process(worker->task);
}
static void idle_worker_timeout(unsigned long __pool)
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
{
struct worker_pool *pool = (void *)__pool;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
spin_lock_irq(&pool->lock);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
while (too_many_workers(pool)) {
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
struct worker *worker;
unsigned long expires;
/* idle_list is kept in LIFO order, check the last one */
worker = list_entry(pool->idle_list.prev, struct worker, entry);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
expires = worker->last_active + IDLE_WORKER_TIMEOUT;
if (time_before(jiffies, expires)) {
mod_timer(&pool->idle_timer, expires);
break;
}
destroy_worker(worker);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
}
spin_unlock_irq(&pool->lock);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
}
static void send_mayday(struct work_struct *work)
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
{
struct pool_workqueue *pwq = get_work_pwq(work);
struct workqueue_struct *wq = pwq->wq;
lockdep_assert_held(&wq_mayday_lock);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
if (!wq->rescuer)
return;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
/* mayday mayday mayday */
if (list_empty(&pwq->mayday_node)) {
/*
* If @pwq is for an unbound wq, its base ref may be put at
* any time due to an attribute change. Pin @pwq until the
* rescuer is done with it.
*/
get_pwq(pwq);
list_add_tail(&pwq->mayday_node, &wq->maydays);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
wake_up_process(wq->rescuer->task);
}
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
}
static void pool_mayday_timeout(unsigned long __pool)
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
{
struct worker_pool *pool = (void *)__pool;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
struct work_struct *work;
spin_lock_irq(&pool->lock);
spin_lock(&wq_mayday_lock); /* for wq->maydays */
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
if (need_to_create_worker(pool)) {
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
/*
* We've been trying to create a new worker but
* haven't been successful. We might be hitting an
* allocation deadlock. Send distress signals to
* rescuers.
*/
list_for_each_entry(work, &pool->worklist, entry)
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
send_mayday(work);
}
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
spin_unlock(&wq_mayday_lock);
spin_unlock_irq(&pool->lock);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
mod_timer(&pool->mayday_timer, jiffies + MAYDAY_INTERVAL);
}
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
/**
* maybe_create_worker - create a new worker if necessary
* @pool: pool to create a new worker for
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
*
* Create a new worker for @pool if necessary. @pool is guaranteed to
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
* have at least one idle worker on return from this function. If
* creating a new worker takes longer than MAYDAY_INTERVAL, mayday is
* sent to all rescuers with works scheduled on @pool to resolve
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
* possible allocation deadlock.
*
* On return, need_to_create_worker() is guaranteed to be %false and
* may_start_working() %true.
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
*
* LOCKING:
* spin_lock_irq(pool->lock) which may be released and regrabbed
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
* multiple times. Does GFP_KERNEL allocations. Called only from
* manager.
*/
workqueue: fix subtle pool management issue which can stall whole worker_pool A worker_pool's forward progress is guaranteed by the fact that the last idle worker assumes the manager role to create more workers and summon the rescuers if creating workers doesn't succeed in timely manner before proceeding to execute work items. This manager role is implemented in manage_workers(), which indicates whether the worker may proceed to work item execution with its return value. This is necessary because multiple workers may contend for the manager role, and, if there already is a manager, others should proceed to work item execution. Unfortunately, the function also indicates that the worker may proceed to work item execution if need_to_create_worker() is false at the head of the function. need_to_create_worker() tests the following conditions. pending work items && !nr_running && !nr_idle The first and third conditions are protected by pool->lock and thus won't change while holding pool->lock; however, nr_running can change asynchronously as other workers block and resume and while it's likely to be zero, as someone woke this worker up in the first place, some other workers could have become runnable inbetween making it non-zero. If this happens, manage_worker() could return false even with zero nr_idle making the worker, the last idle one, proceed to execute work items. If then all workers of the pool end up blocking on a resource which can only be released by a work item which is pending on that pool, the whole pool can deadlock as there's no one to create more workers or summon the rescuers. This patch fixes the problem by removing the early exit condition from maybe_create_worker() and making manage_workers() return false iff there's already another manager, which ensures that the last worker doesn't start executing work items. We can leave the early exit condition alone and just ignore the return value but the only reason it was put there is because the manage_workers() used to perform both creations and destructions of workers and thus the function may be invoked while the pool is trying to reduce the number of workers. Now that manage_workers() is called only when more workers are needed, the only case this early exit condition is triggered is rare race conditions rendering it pointless. Tested with simulated workload and modified workqueue code which trigger the pool deadlock reliably without this patch. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Eric Sandeen <sandeen@sandeen.net> Link: http://lkml.kernel.org/g/54B019F4.8030009@sandeen.net Cc: Dave Chinner <david@fromorbit.com> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: stable@vger.kernel.org
2015-01-16 19:21:16 +00:00
static void maybe_create_worker(struct worker_pool *pool)
__releases(&pool->lock)
__acquires(&pool->lock)
{
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
restart:
spin_unlock_irq(&pool->lock);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
/* if we don't make progress in MAYDAY_INITIAL_TIMEOUT, call for help */
mod_timer(&pool->mayday_timer, jiffies + MAYDAY_INITIAL_TIMEOUT);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
while (true) {
if (create_worker(pool) || !need_to_create_worker(pool))
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
break;
schedule_timeout_interruptible(CREATE_COOLDOWN);
if (!need_to_create_worker(pool))
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
break;
}
del_timer_sync(&pool->mayday_timer);
spin_lock_irq(&pool->lock);
/*
* This is necessary even after a new worker was just successfully
* created as @pool->lock was dropped and the new worker might have
* already become busy.
*/
if (need_to_create_worker(pool))
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
goto restart;
}
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
/**
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
* manage_workers - manage worker pool
* @worker: self
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
*
* Assume the manager role and manage the worker pool @worker belongs
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
* to. At any given time, there can be only zero or one manager per
* pool. The exclusion is handled automatically by this function.
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
*
* The caller can safely start processing works on false return. On
* true return, it's guaranteed that need_to_create_worker() is false
* and may_start_working() is true.
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
*
* CONTEXT:
* spin_lock_irq(pool->lock) which may be released and regrabbed
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
* multiple times. Does GFP_KERNEL allocations.
*
* Return:
workqueue: fix subtle pool management issue which can stall whole worker_pool A worker_pool's forward progress is guaranteed by the fact that the last idle worker assumes the manager role to create more workers and summon the rescuers if creating workers doesn't succeed in timely manner before proceeding to execute work items. This manager role is implemented in manage_workers(), which indicates whether the worker may proceed to work item execution with its return value. This is necessary because multiple workers may contend for the manager role, and, if there already is a manager, others should proceed to work item execution. Unfortunately, the function also indicates that the worker may proceed to work item execution if need_to_create_worker() is false at the head of the function. need_to_create_worker() tests the following conditions. pending work items && !nr_running && !nr_idle The first and third conditions are protected by pool->lock and thus won't change while holding pool->lock; however, nr_running can change asynchronously as other workers block and resume and while it's likely to be zero, as someone woke this worker up in the first place, some other workers could have become runnable inbetween making it non-zero. If this happens, manage_worker() could return false even with zero nr_idle making the worker, the last idle one, proceed to execute work items. If then all workers of the pool end up blocking on a resource which can only be released by a work item which is pending on that pool, the whole pool can deadlock as there's no one to create more workers or summon the rescuers. This patch fixes the problem by removing the early exit condition from maybe_create_worker() and making manage_workers() return false iff there's already another manager, which ensures that the last worker doesn't start executing work items. We can leave the early exit condition alone and just ignore the return value but the only reason it was put there is because the manage_workers() used to perform both creations and destructions of workers and thus the function may be invoked while the pool is trying to reduce the number of workers. Now that manage_workers() is called only when more workers are needed, the only case this early exit condition is triggered is rare race conditions rendering it pointless. Tested with simulated workload and modified workqueue code which trigger the pool deadlock reliably without this patch. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Eric Sandeen <sandeen@sandeen.net> Link: http://lkml.kernel.org/g/54B019F4.8030009@sandeen.net Cc: Dave Chinner <david@fromorbit.com> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: stable@vger.kernel.org
2015-01-16 19:21:16 +00:00
* %false if the pool doesn't need management and the caller can safely
* start processing works, %true if management function was performed and
* the conditions that the caller verified before calling the function may
* no longer be true.
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
*/
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
static bool manage_workers(struct worker *worker)
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
{
struct worker_pool *pool = worker->pool;
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
/*
* Anyone who successfully grabs manager_arb wins the arbitration
* and becomes the manager. mutex_trylock() on pool->manager_arb
* failure while holding pool->lock reliably indicates that someone
* else is managing the pool and the worker which failed trylock
* can proceed to executing work items. This means that anyone
* grabbing manager_arb is responsible for actually performing
* manager duties. If manager_arb is grabbed and released without
* actual management, the pool may stall indefinitely.
*/
if (!mutex_trylock(&pool->manager_arb))
workqueue: fix subtle pool management issue which can stall whole worker_pool A worker_pool's forward progress is guaranteed by the fact that the last idle worker assumes the manager role to create more workers and summon the rescuers if creating workers doesn't succeed in timely manner before proceeding to execute work items. This manager role is implemented in manage_workers(), which indicates whether the worker may proceed to work item execution with its return value. This is necessary because multiple workers may contend for the manager role, and, if there already is a manager, others should proceed to work item execution. Unfortunately, the function also indicates that the worker may proceed to work item execution if need_to_create_worker() is false at the head of the function. need_to_create_worker() tests the following conditions. pending work items && !nr_running && !nr_idle The first and third conditions are protected by pool->lock and thus won't change while holding pool->lock; however, nr_running can change asynchronously as other workers block and resume and while it's likely to be zero, as someone woke this worker up in the first place, some other workers could have become runnable inbetween making it non-zero. If this happens, manage_worker() could return false even with zero nr_idle making the worker, the last idle one, proceed to execute work items. If then all workers of the pool end up blocking on a resource which can only be released by a work item which is pending on that pool, the whole pool can deadlock as there's no one to create more workers or summon the rescuers. This patch fixes the problem by removing the early exit condition from maybe_create_worker() and making manage_workers() return false iff there's already another manager, which ensures that the last worker doesn't start executing work items. We can leave the early exit condition alone and just ignore the return value but the only reason it was put there is because the manage_workers() used to perform both creations and destructions of workers and thus the function may be invoked while the pool is trying to reduce the number of workers. Now that manage_workers() is called only when more workers are needed, the only case this early exit condition is triggered is rare race conditions rendering it pointless. Tested with simulated workload and modified workqueue code which trigger the pool deadlock reliably without this patch. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Eric Sandeen <sandeen@sandeen.net> Link: http://lkml.kernel.org/g/54B019F4.8030009@sandeen.net Cc: Dave Chinner <david@fromorbit.com> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: stable@vger.kernel.org
2015-01-16 19:21:16 +00:00
return false;
pool->manager = worker;
workqueue: fix subtle pool management issue which can stall whole worker_pool A worker_pool's forward progress is guaranteed by the fact that the last idle worker assumes the manager role to create more workers and summon the rescuers if creating workers doesn't succeed in timely manner before proceeding to execute work items. This manager role is implemented in manage_workers(), which indicates whether the worker may proceed to work item execution with its return value. This is necessary because multiple workers may contend for the manager role, and, if there already is a manager, others should proceed to work item execution. Unfortunately, the function also indicates that the worker may proceed to work item execution if need_to_create_worker() is false at the head of the function. need_to_create_worker() tests the following conditions. pending work items && !nr_running && !nr_idle The first and third conditions are protected by pool->lock and thus won't change while holding pool->lock; however, nr_running can change asynchronously as other workers block and resume and while it's likely to be zero, as someone woke this worker up in the first place, some other workers could have become runnable inbetween making it non-zero. If this happens, manage_worker() could return false even with zero nr_idle making the worker, the last idle one, proceed to execute work items. If then all workers of the pool end up blocking on a resource which can only be released by a work item which is pending on that pool, the whole pool can deadlock as there's no one to create more workers or summon the rescuers. This patch fixes the problem by removing the early exit condition from maybe_create_worker() and making manage_workers() return false iff there's already another manager, which ensures that the last worker doesn't start executing work items. We can leave the early exit condition alone and just ignore the return value but the only reason it was put there is because the manage_workers() used to perform both creations and destructions of workers and thus the function may be invoked while the pool is trying to reduce the number of workers. Now that manage_workers() is called only when more workers are needed, the only case this early exit condition is triggered is rare race conditions rendering it pointless. Tested with simulated workload and modified workqueue code which trigger the pool deadlock reliably without this patch. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Eric Sandeen <sandeen@sandeen.net> Link: http://lkml.kernel.org/g/54B019F4.8030009@sandeen.net Cc: Dave Chinner <david@fromorbit.com> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: stable@vger.kernel.org
2015-01-16 19:21:16 +00:00
maybe_create_worker(pool);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
pool->manager = NULL;
mutex_unlock(&pool->manager_arb);
workqueue: fix subtle pool management issue which can stall whole worker_pool A worker_pool's forward progress is guaranteed by the fact that the last idle worker assumes the manager role to create more workers and summon the rescuers if creating workers doesn't succeed in timely manner before proceeding to execute work items. This manager role is implemented in manage_workers(), which indicates whether the worker may proceed to work item execution with its return value. This is necessary because multiple workers may contend for the manager role, and, if there already is a manager, others should proceed to work item execution. Unfortunately, the function also indicates that the worker may proceed to work item execution if need_to_create_worker() is false at the head of the function. need_to_create_worker() tests the following conditions. pending work items && !nr_running && !nr_idle The first and third conditions are protected by pool->lock and thus won't change while holding pool->lock; however, nr_running can change asynchronously as other workers block and resume and while it's likely to be zero, as someone woke this worker up in the first place, some other workers could have become runnable inbetween making it non-zero. If this happens, manage_worker() could return false even with zero nr_idle making the worker, the last idle one, proceed to execute work items. If then all workers of the pool end up blocking on a resource which can only be released by a work item which is pending on that pool, the whole pool can deadlock as there's no one to create more workers or summon the rescuers. This patch fixes the problem by removing the early exit condition from maybe_create_worker() and making manage_workers() return false iff there's already another manager, which ensures that the last worker doesn't start executing work items. We can leave the early exit condition alone and just ignore the return value but the only reason it was put there is because the manage_workers() used to perform both creations and destructions of workers and thus the function may be invoked while the pool is trying to reduce the number of workers. Now that manage_workers() is called only when more workers are needed, the only case this early exit condition is triggered is rare race conditions rendering it pointless. Tested with simulated workload and modified workqueue code which trigger the pool deadlock reliably without this patch. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Eric Sandeen <sandeen@sandeen.net> Link: http://lkml.kernel.org/g/54B019F4.8030009@sandeen.net Cc: Dave Chinner <david@fromorbit.com> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: stable@vger.kernel.org
2015-01-16 19:21:16 +00:00
return true;
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
}
/**
* process_one_work - process single work
* @worker: self
* @work: work to process
*
* Process @work. This function contains all the logics necessary to
* process a single work including synchronization against and
* interaction with other workers on the same cpu, queueing and
* flushing. As long as context requirement is met, any worker can
* call this function to process a work.
*
* CONTEXT:
* spin_lock_irq(pool->lock) which is released and regrabbed.
*/
static void process_one_work(struct worker *worker, struct work_struct *work)
__releases(&pool->lock)
__acquires(&pool->lock)
{
struct pool_workqueue *pwq = get_work_pwq(work);
struct worker_pool *pool = worker->pool;
bool cpu_intensive = pwq->wq->flags & WQ_CPU_INTENSIVE;
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
int work_color;
workqueue: use shared worklist and pool all workers per cpu Use gcwq->worklist instead of cwq->worklist and break the strict association between a cwq and its worker. All works queued on a cpu are queued on gcwq->worklist and processed by any available worker on the gcwq. As there no longer is strict association between a cwq and its worker, whether a work is executing can now only be determined by calling [__]find_worker_executing_work(). After this change, the only association between a cwq and its worker is that a cwq puts a worker into shared worker pool on creation and kills it on destruction. As all workqueues are still limited to max_active of one, this means that there are always at least as many workers as active works and thus there's no danger for deadlock. The break of strong association between cwqs and workers requires somewhat clumsy changes to current_is_keventd() and destroy_workqueue(). Dynamic worker pool management will remove both clumsy changes. current_is_keventd() won't be necessary at all as the only reason it exists is to avoid queueing a work from a work which will be allowed just fine. The clumsy part of destroy_workqueue() is added because a worker can only be destroyed while idle and there's no guarantee a worker is idle when its wq is going down. With dynamic pool management, workers are not associated with workqueues at all and only idle ones will be submitted to destroy_workqueue() so the code won't be necessary anymore. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:13 +00:00
struct worker *collision;
#ifdef CONFIG_LOCKDEP
/*
* It is permissible to free the struct work_struct from
* inside the function that is called from it, this we need to
* take into account for lockdep too. To avoid bogus "held
* lock freed" warnings as well as problems when looking into
* work->lockdep_map, make a copy and use that here.
*/
lockdep: fix oops in processing workqueue Under memory load, on x86_64, with lockdep enabled, the workqueue's process_one_work() has been seen to oops in __lock_acquire(), barfing on a 0xffffffff00000000 pointer in the lockdep_map's class_cache[]. Because it's permissible to free a work_struct from its callout function, the map used is an onstack copy of the map given in the work_struct: and that copy is made without any locking. Surprisingly, gcc (4.5.1 in Hugh's case) uses "rep movsl" rather than "rep movsq" for that structure copy: which might race with a workqueue user's wait_on_work() doing lock_map_acquire() on the source of the copy, putting a pointer into the class_cache[], but only in time for the top half of that pointer to be copied to the destination map. Boom when process_one_work() subsequently does lock_map_acquire() on its onstack copy of the lockdep_map. Fix this, and a similar instance in call_timer_fn(), with a lockdep_copy_map() function which additionally NULLs the class_cache[]. Note: this oops was actually seen on 3.4-next, where flush_work() newly does the racing lock_map_acquire(); but Tejun points out that 3.4 and earlier are already vulnerable to the same through wait_on_work(). * Patch orginally from Peter. Hugh modified it a bit and wrote the description. Signed-off-by: Peter Zijlstra <peterz@infradead.org> Reported-by: Hugh Dickins <hughd@google.com> LKML-Reference: <alpine.LSU.2.00.1205070951170.1544@eggly.anvils> Signed-off-by: Tejun Heo <tj@kernel.org>
2012-05-15 15:06:19 +00:00
struct lockdep_map lockdep_map;
lockdep_copy_map(&lockdep_map, &work->lockdep_map);
#endif
/* ensure we're on the correct CPU */
WARN_ON_ONCE(!(pool->flags & POOL_DISASSOCIATED) &&
raw_smp_processor_id() != pool->cpu);
workqueue: reimplement CPU online rebinding to handle idle workers Currently, if there are left workers when a CPU is being brough back online, the trustee kills all idle workers and scheduled rebind_work so that they re-bind to the CPU after the currently executing work is finished. This works for busy workers because concurrency management doesn't try to wake up them from scheduler callbacks, which require the target task to be on the local run queue. The busy worker bumps concurrency counter appropriately as it clears WORKER_UNBOUND from the rebind work item and it's bound to the CPU before returning to the idle state. To reduce CPU on/offlining overhead (as many embedded systems use it for powersaving) and simplify the code path, workqueue is planned to be modified to retain idle workers across CPU on/offlining. This patch reimplements CPU online rebinding such that it can also handle idle workers. As noted earlier, due to the local wakeup requirement, rebinding idle workers is tricky. All idle workers must be re-bound before scheduler callbacks are enabled. This is achieved by interlocking idle re-binding. Idle workers are requested to re-bind and then hold until all idle re-binding is complete so that no bound worker starts executing work item. Only after all idle workers are re-bound and parked, CPU_ONLINE proceeds to release them and queue rebind work item to busy workers thus guaranteeing scheduler callbacks aren't invoked until all idle workers are ready. worker_rebind_fn() is renamed to busy_worker_rebind_fn() and idle_worker_rebind() for idle workers is added. Rebinding logic is moved to rebind_workers() and now called from CPU_ONLINE after flushing trustee. While at it, add CPU sanity check in worker_thread(). Note that now a worker may become idle or the manager between trustee release and rebinding during CPU_ONLINE. As the previous patch updated create_worker() so that it can be used by regular manager while unbound and this patch implements idle re-binding, this is safe. This prepares for removal of trustee and keeping idle workers across CPU hotplugs. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: "Rafael J. Wysocki" <rjw@sisk.pl>
2012-07-17 19:39:27 +00:00
workqueue: use shared worklist and pool all workers per cpu Use gcwq->worklist instead of cwq->worklist and break the strict association between a cwq and its worker. All works queued on a cpu are queued on gcwq->worklist and processed by any available worker on the gcwq. As there no longer is strict association between a cwq and its worker, whether a work is executing can now only be determined by calling [__]find_worker_executing_work(). After this change, the only association between a cwq and its worker is that a cwq puts a worker into shared worker pool on creation and kills it on destruction. As all workqueues are still limited to max_active of one, this means that there are always at least as many workers as active works and thus there's no danger for deadlock. The break of strong association between cwqs and workers requires somewhat clumsy changes to current_is_keventd() and destroy_workqueue(). Dynamic worker pool management will remove both clumsy changes. current_is_keventd() won't be necessary at all as the only reason it exists is to avoid queueing a work from a work which will be allowed just fine. The clumsy part of destroy_workqueue() is added because a worker can only be destroyed while idle and there's no guarantee a worker is idle when its wq is going down. With dynamic pool management, workers are not associated with workqueues at all and only idle ones will be submitted to destroy_workqueue() so the code won't be necessary anymore. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:13 +00:00
/*
* A single work shouldn't be executed concurrently by
* multiple workers on a single cpu. Check whether anyone is
* already processing the work. If so, defer the work to the
* currently executing one.
*/
collision = find_worker_executing_work(pool, work);
workqueue: use shared worklist and pool all workers per cpu Use gcwq->worklist instead of cwq->worklist and break the strict association between a cwq and its worker. All works queued on a cpu are queued on gcwq->worklist and processed by any available worker on the gcwq. As there no longer is strict association between a cwq and its worker, whether a work is executing can now only be determined by calling [__]find_worker_executing_work(). After this change, the only association between a cwq and its worker is that a cwq puts a worker into shared worker pool on creation and kills it on destruction. As all workqueues are still limited to max_active of one, this means that there are always at least as many workers as active works and thus there's no danger for deadlock. The break of strong association between cwqs and workers requires somewhat clumsy changes to current_is_keventd() and destroy_workqueue(). Dynamic worker pool management will remove both clumsy changes. current_is_keventd() won't be necessary at all as the only reason it exists is to avoid queueing a work from a work which will be allowed just fine. The clumsy part of destroy_workqueue() is added because a worker can only be destroyed while idle and there's no guarantee a worker is idle when its wq is going down. With dynamic pool management, workers are not associated with workqueues at all and only idle ones will be submitted to destroy_workqueue() so the code won't be necessary anymore. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:13 +00:00
if (unlikely(collision)) {
move_linked_works(work, &collision->scheduled, NULL);
return;
}
workqueue: disable irq while manipulating PENDING Queueing operations use WORK_STRUCT_PENDING_BIT to synchronize access to the target work item. They first try to claim the bit and proceed with queueing only after that succeeds and there's a window between PENDING being set and the actual queueing where the task can be interrupted or preempted. There's also a similar window in process_one_work() when clearing PENDING. A work item is dequeued, gcwq->lock is released and then PENDING is cleared and the worker might get interrupted or preempted between releasing gcwq->lock and clearing PENDING. cancel[_delayed]_work_sync() tries to claim or steal PENDING. The function assumes that a work item with PENDING is either queued or in the process of being [de]queued. In the latter case, it busy-loops until either the work item loses PENDING or is queued. If canceling coincides with the above described interrupts or preemptions, the canceling task will busy-loop while the queueing or executing task is preempted. This patch keeps irq disabled across claiming PENDING and actual queueing and moves PENDING clearing in process_one_work() inside gcwq->lock so that busy looping from PENDING && !queued doesn't wait for interrupted/preempted tasks. Note that, in process_one_work(), setting last CPU and clearing PENDING got merged into single operation. This removes possible long busy-loops and will allow using try_to_grab_pending() from bh and irq contexts. v2: __queue_work() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Disable irq instead of preemption. IRQ will be disabled while grabbing gcwq->lock later anyway and this allows using try_to_grab_pending() from bh and irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:45 +00:00
/* claim and dequeue */
debug_work_deactivate(work);
hash_add(pool->busy_hash, &worker->hentry, (unsigned long)work);
worker->current_work = work;
workqueue: consider work function when searching for busy work items To avoid executing the same work item concurrenlty, workqueue hashes currently busy workers according to their current work items and looks up the the table when it wants to execute a new work item. If there already is a worker which is executing the new work item, the new item is queued to the found worker so that it gets executed only after the current execution finishes. Unfortunately, a work item may be freed while being executed and thus recycled for different purposes. If it gets recycled for a different work item and queued while the previous execution is still in progress, workqueue may make the new work item wait for the old one although the two aren't really related in any way. In extreme cases, this false dependency may lead to deadlock although it's extremely unlikely given that there aren't too many self-freeing work item users and they usually don't wait for other work items. To alleviate the problem, record the current work function in each busy worker and match it together with the work item address in find_worker_executing_work(). While this isn't complete, it ensures that unrelated work items don't interact with each other and in the very unlikely case where a twisted wq user triggers it, it's always onto itself making the culprit easy to spot. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Andrey Isakov <andy51@gmx.ru> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=51701 Cc: stable@vger.kernel.org
2012-12-18 18:35:02 +00:00
worker->current_func = work->func;
worker->current_pwq = pwq;
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
work_color = get_work_color(work);
list_del_init(&work->entry);
/*
* CPU intensive works don't participate in concurrency management.
* They're the scheduler's responsibility. This takes @worker out
* of concurrency management and the next code block will chain
* execution of the pending work items.
*/
if (unlikely(cpu_intensive))
worker_set_flags(worker, WORKER_CPU_INTENSIVE);
/*
* Wake up another worker if necessary. The condition is always
* false for normal per-cpu workers since nr_running would always
* be >= 1 at this point. This is used to chain execution of the
* pending work items for WORKER_NOT_RUNNING workers such as the
* UNBOUND and CPU_INTENSIVE ones.
*/
if (need_more_worker(pool))
wake_up_worker(pool);
workqueue: disable irq while manipulating PENDING Queueing operations use WORK_STRUCT_PENDING_BIT to synchronize access to the target work item. They first try to claim the bit and proceed with queueing only after that succeeds and there's a window between PENDING being set and the actual queueing where the task can be interrupted or preempted. There's also a similar window in process_one_work() when clearing PENDING. A work item is dequeued, gcwq->lock is released and then PENDING is cleared and the worker might get interrupted or preempted between releasing gcwq->lock and clearing PENDING. cancel[_delayed]_work_sync() tries to claim or steal PENDING. The function assumes that a work item with PENDING is either queued or in the process of being [de]queued. In the latter case, it busy-loops until either the work item loses PENDING or is queued. If canceling coincides with the above described interrupts or preemptions, the canceling task will busy-loop while the queueing or executing task is preempted. This patch keeps irq disabled across claiming PENDING and actual queueing and moves PENDING clearing in process_one_work() inside gcwq->lock so that busy looping from PENDING && !queued doesn't wait for interrupted/preempted tasks. Note that, in process_one_work(), setting last CPU and clearing PENDING got merged into single operation. This removes possible long busy-loops and will allow using try_to_grab_pending() from bh and irq contexts. v2: __queue_work() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Disable irq instead of preemption. IRQ will be disabled while grabbing gcwq->lock later anyway and this allows using try_to_grab_pending() from bh and irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:45 +00:00
/*
* Record the last pool and clear PENDING which should be the last
* update to @work. Also, do this inside @pool->lock so that
* PENDING and queued state changes happen together while IRQ is
* disabled.
workqueue: disable irq while manipulating PENDING Queueing operations use WORK_STRUCT_PENDING_BIT to synchronize access to the target work item. They first try to claim the bit and proceed with queueing only after that succeeds and there's a window between PENDING being set and the actual queueing where the task can be interrupted or preempted. There's also a similar window in process_one_work() when clearing PENDING. A work item is dequeued, gcwq->lock is released and then PENDING is cleared and the worker might get interrupted or preempted between releasing gcwq->lock and clearing PENDING. cancel[_delayed]_work_sync() tries to claim or steal PENDING. The function assumes that a work item with PENDING is either queued or in the process of being [de]queued. In the latter case, it busy-loops until either the work item loses PENDING or is queued. If canceling coincides with the above described interrupts or preemptions, the canceling task will busy-loop while the queueing or executing task is preempted. This patch keeps irq disabled across claiming PENDING and actual queueing and moves PENDING clearing in process_one_work() inside gcwq->lock so that busy looping from PENDING && !queued doesn't wait for interrupted/preempted tasks. Note that, in process_one_work(), setting last CPU and clearing PENDING got merged into single operation. This removes possible long busy-loops and will allow using try_to_grab_pending() from bh and irq contexts. v2: __queue_work() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Disable irq instead of preemption. IRQ will be disabled while grabbing gcwq->lock later anyway and this allows using try_to_grab_pending() from bh and irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:45 +00:00
*/
set_work_pool_and_clear_pending(work, pool->id);
spin_unlock_irq(&pool->lock);
lock_map_acquire_read(&pwq->wq->lockdep_map);
lock_map_acquire(&lockdep_map);
trace_workqueue_execute_start(work);
workqueue: consider work function when searching for busy work items To avoid executing the same work item concurrenlty, workqueue hashes currently busy workers according to their current work items and looks up the the table when it wants to execute a new work item. If there already is a worker which is executing the new work item, the new item is queued to the found worker so that it gets executed only after the current execution finishes. Unfortunately, a work item may be freed while being executed and thus recycled for different purposes. If it gets recycled for a different work item and queued while the previous execution is still in progress, workqueue may make the new work item wait for the old one although the two aren't really related in any way. In extreme cases, this false dependency may lead to deadlock although it's extremely unlikely given that there aren't too many self-freeing work item users and they usually don't wait for other work items. To alleviate the problem, record the current work function in each busy worker and match it together with the work item address in find_worker_executing_work(). While this isn't complete, it ensures that unrelated work items don't interact with each other and in the very unlikely case where a twisted wq user triggers it, it's always onto itself making the culprit easy to spot. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Andrey Isakov <andy51@gmx.ru> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=51701 Cc: stable@vger.kernel.org
2012-12-18 18:35:02 +00:00
worker->current_func(work);
/*
* While we must be careful to not use "work" after this, the trace
* point will only record its address.
*/
trace_workqueue_execute_end(work);
lock_map_release(&lockdep_map);
lock_map_release(&pwq->wq->lockdep_map);
if (unlikely(in_atomic() || lockdep_depth(current) > 0)) {
pr_err("BUG: workqueue leaked lock or atomic: %s/0x%08x/%d\n"
" last function: %pf\n",
workqueue: consider work function when searching for busy work items To avoid executing the same work item concurrenlty, workqueue hashes currently busy workers according to their current work items and looks up the the table when it wants to execute a new work item. If there already is a worker which is executing the new work item, the new item is queued to the found worker so that it gets executed only after the current execution finishes. Unfortunately, a work item may be freed while being executed and thus recycled for different purposes. If it gets recycled for a different work item and queued while the previous execution is still in progress, workqueue may make the new work item wait for the old one although the two aren't really related in any way. In extreme cases, this false dependency may lead to deadlock although it's extremely unlikely given that there aren't too many self-freeing work item users and they usually don't wait for other work items. To alleviate the problem, record the current work function in each busy worker and match it together with the work item address in find_worker_executing_work(). While this isn't complete, it ensures that unrelated work items don't interact with each other and in the very unlikely case where a twisted wq user triggers it, it's always onto itself making the culprit easy to spot. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Andrey Isakov <andy51@gmx.ru> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=51701 Cc: stable@vger.kernel.org
2012-12-18 18:35:02 +00:00
current->comm, preempt_count(), task_pid_nr(current),
worker->current_func);
debug_show_held_locks(current);
dump_stack();
}
/*
* The following prevents a kworker from hogging CPU on !PREEMPT
* kernels, where a requeueing work item waiting for something to
* happen could deadlock with stop_machine as such work item could
* indefinitely requeue itself while all other CPUs are trapped in
* stop_machine. At the same time, report a quiescent RCU state so
* the same condition doesn't freeze RCU.
*/
cond_resched_rcu_qs();
spin_lock_irq(&pool->lock);
/* clear cpu intensive status */
if (unlikely(cpu_intensive))
worker_clr_flags(worker, WORKER_CPU_INTENSIVE);
/* we're done with it, release */
hash_del(&worker->hentry);
worker->current_work = NULL;
workqueue: consider work function when searching for busy work items To avoid executing the same work item concurrenlty, workqueue hashes currently busy workers according to their current work items and looks up the the table when it wants to execute a new work item. If there already is a worker which is executing the new work item, the new item is queued to the found worker so that it gets executed only after the current execution finishes. Unfortunately, a work item may be freed while being executed and thus recycled for different purposes. If it gets recycled for a different work item and queued while the previous execution is still in progress, workqueue may make the new work item wait for the old one although the two aren't really related in any way. In extreme cases, this false dependency may lead to deadlock although it's extremely unlikely given that there aren't too many self-freeing work item users and they usually don't wait for other work items. To alleviate the problem, record the current work function in each busy worker and match it together with the work item address in find_worker_executing_work(). While this isn't complete, it ensures that unrelated work items don't interact with each other and in the very unlikely case where a twisted wq user triggers it, it's always onto itself making the culprit easy to spot. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Andrey Isakov <andy51@gmx.ru> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=51701 Cc: stable@vger.kernel.org
2012-12-18 18:35:02 +00:00
worker->current_func = NULL;
worker->current_pwq = NULL;
workqueue: include workqueue info when printing debug dump of a worker task One of the problems that arise when converting dedicated custom threadpool to workqueue is that the shared worker pool used by workqueue anonimizes each worker making it more difficult to identify what the worker was doing on which target from the output of sysrq-t or debug dump from oops, BUG() and friends. This patch implements set_worker_desc() which can be called from any workqueue work function to set its description. When the worker task is dumped for whatever reason - sysrq-t, WARN, BUG, oops, lockdep assertion and so on - the description will be printed out together with the workqueue name and the worker function pointer. The printing side is implemented by print_worker_info() which is called from functions in task dump paths - sched_show_task() and dump_stack_print_info(). print_worker_info() can be safely called on any task in any state as long as the task struct itself is accessible. It uses probe_*() functions to access worker fields. It may print garbage if something went very wrong, but it wouldn't cause (another) oops. The description is currently limited to 24bytes including the terminating \0. worker->desc_valid and workder->desc[] are added and the 64 bytes marker which was already incorrect before adding the new fields is moved to the correct position. Here's an example dump with writeback updated to set the bdi name as worker desc. Hardware name: Bochs Modules linked in: Pid: 7, comm: kworker/u9:0 Not tainted 3.9.0-rc1-work+ #1 Workqueue: writeback bdi_writeback_workfn (flush-8:0) ffffffff820a3ab0 ffff88000f6e9cb8 ffffffff81c61845 ffff88000f6e9cf8 ffffffff8108f50f 0000000000000000 0000000000000000 ffff88000cde16b0 ffff88000cde1aa8 ffff88001ee19240 ffff88000f6e9fd8 ffff88000f6e9d08 Call Trace: [<ffffffff81c61845>] dump_stack+0x19/0x1b [<ffffffff8108f50f>] warn_slowpath_common+0x7f/0xc0 [<ffffffff8108f56a>] warn_slowpath_null+0x1a/0x20 [<ffffffff81200150>] bdi_writeback_workfn+0x2a0/0x3b0 ... Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com> Acked-by: Jan Kara <jack@suse.cz> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Dave Chinner <david@fromorbit.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-04-30 22:27:22 +00:00
worker->desc_valid = false;
pwq_dec_nr_in_flight(pwq, work_color);
}
/**
* process_scheduled_works - process scheduled works
* @worker: self
*
* Process all scheduled works. Please note that the scheduled list
* may change while processing a work, so this function repeatedly
* fetches a work from the top and executes it.
*
* CONTEXT:
* spin_lock_irq(pool->lock) which may be released and regrabbed
* multiple times.
*/
static void process_scheduled_works(struct worker *worker)
{
while (!list_empty(&worker->scheduled)) {
struct work_struct *work = list_first_entry(&worker->scheduled,
struct work_struct, entry);
process_one_work(worker, work);
}
}
/**
* worker_thread - the worker thread function
* @__worker: self
*
* The worker thread function. All workers belong to a worker_pool -
* either a per-cpu one or dynamic unbound one. These workers process all
* work items regardless of their specific target workqueue. The only
* exception is work items which belong to workqueues with a rescuer which
* will be explained in rescuer_thread().
*
* Return: 0
*/
static int worker_thread(void *__worker)
{
struct worker *worker = __worker;
struct worker_pool *pool = worker->pool;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
/* tell the scheduler that this is a workqueue worker */
worker->task->flags |= PF_WQ_WORKER;
woke_up:
spin_lock_irq(&pool->lock);
workqueue: directly restore CPU affinity of workers from CPU_ONLINE Rebinding workers of a per-cpu pool after a CPU comes online involves a lot of back-and-forth mostly because only the task itself could adjust CPU affinity if PF_THREAD_BOUND was set. As CPU_ONLINE itself couldn't adjust affinity, it had to somehow coerce the workers themselves to perform set_cpus_allowed_ptr(). Due to the various states a worker can be in, this led to three different paths a worker may be rebound. worker->rebind_work is queued to busy workers. Idle ones are signaled by unlinking worker->entry and call idle_worker_rebind(). The manager isn't covered by either and implements its own mechanism. PF_THREAD_BOUND has been relaced with PF_NO_SETAFFINITY and CPU_ONLINE itself now can manipulate CPU affinity of workers. This patch replaces the existing rebind mechanism with direct one where CPU_ONLINE iterates over all workers using for_each_pool_worker(), restores CPU affinity, and clears WORKER_UNBOUND. There are a couple subtleties. All bound idle workers should have their runqueues set to that of the bound CPU; however, if the target task isn't running, set_cpus_allowed_ptr() just updates the cpus_allowed mask deferring the actual migration to when the task wakes up. This is worked around by waking up idle workers after restoring CPU affinity before any workers can become bound. Another subtlety is stems from matching @pool->nr_running with the number of running unbound workers. While DISASSOCIATED, all workers are unbound and nr_running is zero. As workers become bound again, nr_running needs to be adjusted accordingly; however, there is no good way to tell whether a given worker is running without poking into scheduler internals. Instead of clearing UNBOUND directly, rebind_workers() replaces UNBOUND with another new NOT_RUNNING flag - REBOUND, which will later be cleared by the workers themselves while preparing for the next round of work item execution. The only change needed for the workers is clearing REBOUND along with PREP. * This patch leaves for_each_busy_worker() without any user. Removed. * idle_worker_rebind(), busy_worker_rebind_fn(), worker->rebind_work and rebind logic in manager_workers() removed. * worker_thread() now looks at WORKER_DIE instead of testing whether @worker->entry is empty to determine whether it needs to do something special as dying is the only special thing now. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 20:45:21 +00:00
/* am I supposed to die? */
if (unlikely(worker->flags & WORKER_DIE)) {
spin_unlock_irq(&pool->lock);
workqueue: directly restore CPU affinity of workers from CPU_ONLINE Rebinding workers of a per-cpu pool after a CPU comes online involves a lot of back-and-forth mostly because only the task itself could adjust CPU affinity if PF_THREAD_BOUND was set. As CPU_ONLINE itself couldn't adjust affinity, it had to somehow coerce the workers themselves to perform set_cpus_allowed_ptr(). Due to the various states a worker can be in, this led to three different paths a worker may be rebound. worker->rebind_work is queued to busy workers. Idle ones are signaled by unlinking worker->entry and call idle_worker_rebind(). The manager isn't covered by either and implements its own mechanism. PF_THREAD_BOUND has been relaced with PF_NO_SETAFFINITY and CPU_ONLINE itself now can manipulate CPU affinity of workers. This patch replaces the existing rebind mechanism with direct one where CPU_ONLINE iterates over all workers using for_each_pool_worker(), restores CPU affinity, and clears WORKER_UNBOUND. There are a couple subtleties. All bound idle workers should have their runqueues set to that of the bound CPU; however, if the target task isn't running, set_cpus_allowed_ptr() just updates the cpus_allowed mask deferring the actual migration to when the task wakes up. This is worked around by waking up idle workers after restoring CPU affinity before any workers can become bound. Another subtlety is stems from matching @pool->nr_running with the number of running unbound workers. While DISASSOCIATED, all workers are unbound and nr_running is zero. As workers become bound again, nr_running needs to be adjusted accordingly; however, there is no good way to tell whether a given worker is running without poking into scheduler internals. Instead of clearing UNBOUND directly, rebind_workers() replaces UNBOUND with another new NOT_RUNNING flag - REBOUND, which will later be cleared by the workers themselves while preparing for the next round of work item execution. The only change needed for the workers is clearing REBOUND along with PREP. * This patch leaves for_each_busy_worker() without any user. Removed. * idle_worker_rebind(), busy_worker_rebind_fn(), worker->rebind_work and rebind logic in manager_workers() removed. * worker_thread() now looks at WORKER_DIE instead of testing whether @worker->entry is empty to determine whether it needs to do something special as dying is the only special thing now. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 20:45:21 +00:00
WARN_ON_ONCE(!list_empty(&worker->entry));
worker->task->flags &= ~PF_WQ_WORKER;
workqueue: async worker destruction worker destruction includes these parts of code: adjust pool's stats remove the worker from idle list detach the worker from the pool kthread_stop() to wait for the worker's task exit free the worker struct We can find out that there is no essential work to do after kthread_stop(), which means destroy_worker() doesn't need to wait for the worker's task exit, so we can remove kthread_stop() and free the worker struct in the worker exiting path. However, put_unbound_pool() still needs to sync the all the workers' destruction before destroying the pool; otherwise, the workers may access to the invalid pool when they are exiting. So we also move the code of "detach the worker" to the exiting path and let put_unbound_pool() to sync with this code via detach_completion. The code of "detach the worker" is wrapped in a new function "worker_detach_from_pool()" although worker_detach_from_pool() is only called once (in worker_thread()) after this patch, but we need to wrap it for these reasons: 1) The code of "detach the worker" is not short enough to unfold them in worker_thread(). 2) the name of "worker_detach_from_pool()" is self-comment, and we add some comments above the function. 3) it will be shared by rescuer in later patch which allows rescuer and normal thread use the same attach/detach frameworks. The worker id is freed when detaching which happens before the worker is fully dead, but this id of the dying worker may be re-used for a new worker, so the dying worker's task name is changed to "worker/dying" to avoid two or several workers having the same name. Since "detach the worker" is moved out from destroy_worker(), destroy_worker() doesn't require manager_mutex, so the "lockdep_assert_held(&pool->manager_mutex)" in destroy_worker() is removed, and destroy_worker() is not protected by manager_mutex in put_unbound_pool(). tj: Minor description updates. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2014-05-20 09:46:29 +00:00
set_task_comm(worker->task, "kworker/dying");
ida_simple_remove(&pool->worker_ida, worker->id);
workqueue: async worker destruction worker destruction includes these parts of code: adjust pool's stats remove the worker from idle list detach the worker from the pool kthread_stop() to wait for the worker's task exit free the worker struct We can find out that there is no essential work to do after kthread_stop(), which means destroy_worker() doesn't need to wait for the worker's task exit, so we can remove kthread_stop() and free the worker struct in the worker exiting path. However, put_unbound_pool() still needs to sync the all the workers' destruction before destroying the pool; otherwise, the workers may access to the invalid pool when they are exiting. So we also move the code of "detach the worker" to the exiting path and let put_unbound_pool() to sync with this code via detach_completion. The code of "detach the worker" is wrapped in a new function "worker_detach_from_pool()" although worker_detach_from_pool() is only called once (in worker_thread()) after this patch, but we need to wrap it for these reasons: 1) The code of "detach the worker" is not short enough to unfold them in worker_thread(). 2) the name of "worker_detach_from_pool()" is self-comment, and we add some comments above the function. 3) it will be shared by rescuer in later patch which allows rescuer and normal thread use the same attach/detach frameworks. The worker id is freed when detaching which happens before the worker is fully dead, but this id of the dying worker may be re-used for a new worker, so the dying worker's task name is changed to "worker/dying" to avoid two or several workers having the same name. Since "detach the worker" is moved out from destroy_worker(), destroy_worker() doesn't require manager_mutex, so the "lockdep_assert_held(&pool->manager_mutex)" in destroy_worker() is removed, and destroy_worker() is not protected by manager_mutex in put_unbound_pool(). tj: Minor description updates. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2014-05-20 09:46:29 +00:00
worker_detach_from_pool(worker, pool);
kfree(worker);
workqueue: directly restore CPU affinity of workers from CPU_ONLINE Rebinding workers of a per-cpu pool after a CPU comes online involves a lot of back-and-forth mostly because only the task itself could adjust CPU affinity if PF_THREAD_BOUND was set. As CPU_ONLINE itself couldn't adjust affinity, it had to somehow coerce the workers themselves to perform set_cpus_allowed_ptr(). Due to the various states a worker can be in, this led to three different paths a worker may be rebound. worker->rebind_work is queued to busy workers. Idle ones are signaled by unlinking worker->entry and call idle_worker_rebind(). The manager isn't covered by either and implements its own mechanism. PF_THREAD_BOUND has been relaced with PF_NO_SETAFFINITY and CPU_ONLINE itself now can manipulate CPU affinity of workers. This patch replaces the existing rebind mechanism with direct one where CPU_ONLINE iterates over all workers using for_each_pool_worker(), restores CPU affinity, and clears WORKER_UNBOUND. There are a couple subtleties. All bound idle workers should have their runqueues set to that of the bound CPU; however, if the target task isn't running, set_cpus_allowed_ptr() just updates the cpus_allowed mask deferring the actual migration to when the task wakes up. This is worked around by waking up idle workers after restoring CPU affinity before any workers can become bound. Another subtlety is stems from matching @pool->nr_running with the number of running unbound workers. While DISASSOCIATED, all workers are unbound and nr_running is zero. As workers become bound again, nr_running needs to be adjusted accordingly; however, there is no good way to tell whether a given worker is running without poking into scheduler internals. Instead of clearing UNBOUND directly, rebind_workers() replaces UNBOUND with another new NOT_RUNNING flag - REBOUND, which will later be cleared by the workers themselves while preparing for the next round of work item execution. The only change needed for the workers is clearing REBOUND along with PREP. * This patch leaves for_each_busy_worker() without any user. Removed. * idle_worker_rebind(), busy_worker_rebind_fn(), worker->rebind_work and rebind logic in manager_workers() removed. * worker_thread() now looks at WORKER_DIE instead of testing whether @worker->entry is empty to determine whether it needs to do something special as dying is the only special thing now. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 20:45:21 +00:00
return 0;
}
worker_leave_idle(worker);
recheck:
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
/* no more worker necessary? */
if (!need_more_worker(pool))
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
goto sleep;
/* do we need to manage? */
if (unlikely(!may_start_working(pool)) && manage_workers(worker))
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
goto recheck;
/*
* ->scheduled list can only be filled while a worker is
* preparing to process a work or actually processing it.
* Make sure nobody diddled with it while I was sleeping.
*/
WARN_ON_ONCE(!list_empty(&worker->scheduled));
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
/*
workqueue: directly restore CPU affinity of workers from CPU_ONLINE Rebinding workers of a per-cpu pool after a CPU comes online involves a lot of back-and-forth mostly because only the task itself could adjust CPU affinity if PF_THREAD_BOUND was set. As CPU_ONLINE itself couldn't adjust affinity, it had to somehow coerce the workers themselves to perform set_cpus_allowed_ptr(). Due to the various states a worker can be in, this led to three different paths a worker may be rebound. worker->rebind_work is queued to busy workers. Idle ones are signaled by unlinking worker->entry and call idle_worker_rebind(). The manager isn't covered by either and implements its own mechanism. PF_THREAD_BOUND has been relaced with PF_NO_SETAFFINITY and CPU_ONLINE itself now can manipulate CPU affinity of workers. This patch replaces the existing rebind mechanism with direct one where CPU_ONLINE iterates over all workers using for_each_pool_worker(), restores CPU affinity, and clears WORKER_UNBOUND. There are a couple subtleties. All bound idle workers should have their runqueues set to that of the bound CPU; however, if the target task isn't running, set_cpus_allowed_ptr() just updates the cpus_allowed mask deferring the actual migration to when the task wakes up. This is worked around by waking up idle workers after restoring CPU affinity before any workers can become bound. Another subtlety is stems from matching @pool->nr_running with the number of running unbound workers. While DISASSOCIATED, all workers are unbound and nr_running is zero. As workers become bound again, nr_running needs to be adjusted accordingly; however, there is no good way to tell whether a given worker is running without poking into scheduler internals. Instead of clearing UNBOUND directly, rebind_workers() replaces UNBOUND with another new NOT_RUNNING flag - REBOUND, which will later be cleared by the workers themselves while preparing for the next round of work item execution. The only change needed for the workers is clearing REBOUND along with PREP. * This patch leaves for_each_busy_worker() without any user. Removed. * idle_worker_rebind(), busy_worker_rebind_fn(), worker->rebind_work and rebind logic in manager_workers() removed. * worker_thread() now looks at WORKER_DIE instead of testing whether @worker->entry is empty to determine whether it needs to do something special as dying is the only special thing now. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 20:45:21 +00:00
* Finish PREP stage. We're guaranteed to have at least one idle
* worker or that someone else has already assumed the manager
* role. This is where @worker starts participating in concurrency
* management if applicable and concurrency management is restored
* after being rebound. See rebind_workers() for details.
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
*/
workqueue: directly restore CPU affinity of workers from CPU_ONLINE Rebinding workers of a per-cpu pool after a CPU comes online involves a lot of back-and-forth mostly because only the task itself could adjust CPU affinity if PF_THREAD_BOUND was set. As CPU_ONLINE itself couldn't adjust affinity, it had to somehow coerce the workers themselves to perform set_cpus_allowed_ptr(). Due to the various states a worker can be in, this led to three different paths a worker may be rebound. worker->rebind_work is queued to busy workers. Idle ones are signaled by unlinking worker->entry and call idle_worker_rebind(). The manager isn't covered by either and implements its own mechanism. PF_THREAD_BOUND has been relaced with PF_NO_SETAFFINITY and CPU_ONLINE itself now can manipulate CPU affinity of workers. This patch replaces the existing rebind mechanism with direct one where CPU_ONLINE iterates over all workers using for_each_pool_worker(), restores CPU affinity, and clears WORKER_UNBOUND. There are a couple subtleties. All bound idle workers should have their runqueues set to that of the bound CPU; however, if the target task isn't running, set_cpus_allowed_ptr() just updates the cpus_allowed mask deferring the actual migration to when the task wakes up. This is worked around by waking up idle workers after restoring CPU affinity before any workers can become bound. Another subtlety is stems from matching @pool->nr_running with the number of running unbound workers. While DISASSOCIATED, all workers are unbound and nr_running is zero. As workers become bound again, nr_running needs to be adjusted accordingly; however, there is no good way to tell whether a given worker is running without poking into scheduler internals. Instead of clearing UNBOUND directly, rebind_workers() replaces UNBOUND with another new NOT_RUNNING flag - REBOUND, which will later be cleared by the workers themselves while preparing for the next round of work item execution. The only change needed for the workers is clearing REBOUND along with PREP. * This patch leaves for_each_busy_worker() without any user. Removed. * idle_worker_rebind(), busy_worker_rebind_fn(), worker->rebind_work and rebind logic in manager_workers() removed. * worker_thread() now looks at WORKER_DIE instead of testing whether @worker->entry is empty to determine whether it needs to do something special as dying is the only special thing now. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 20:45:21 +00:00
worker_clr_flags(worker, WORKER_PREP | WORKER_REBOUND);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
do {
struct work_struct *work =
list_first_entry(&pool->worklist,
struct work_struct, entry);
workqueue: implement lockup detector Workqueue stalls can happen from a variety of usage bugs such as missing WQ_MEM_RECLAIM flag or concurrency managed work item indefinitely staying RUNNING. These stalls can be extremely difficult to hunt down because the usual warning mechanisms can't detect workqueue stalls and the internal state is pretty opaque. To alleviate the situation, this patch implements workqueue lockup detector. It periodically monitors all worker_pools periodically and, if any pool failed to make forward progress longer than the threshold duration, triggers warning and dumps workqueue state as follows. BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 31s! Showing busy workqueues and worker pools: workqueue events: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=17/256 pending: monkey_wrench_fn, e1000_watchdog, cache_reap, vmstat_shepherd, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, cgroup_release_agent workqueue events_power_efficient: flags=0x80 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=2/256 pending: check_lifetime, neigh_periodic_work workqueue cgroup_pidlist_destroy: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/1 pending: cgroup_pidlist_destroy_work_fn ... The detection mechanism is controller through kernel parameter workqueue.watchdog_thresh and can be updated at runtime through the sysfs module parameter file. v2: Decoupled from softlockup control knobs. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Don Zickus <dzickus@redhat.com> Cc: Ulrich Obergfell <uobergfe@redhat.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Chris Mason <clm@fb.com> Cc: Andrew Morton <akpm@linux-foundation.org>
2015-12-08 16:28:04 +00:00
pool->watchdog_ts = jiffies;
if (likely(!(*work_data_bits(work) & WORK_STRUCT_LINKED))) {
/* optimization path, not strictly necessary */
process_one_work(worker, work);
if (unlikely(!list_empty(&worker->scheduled)))
process_scheduled_works(worker);
} else {
move_linked_works(work, &worker->scheduled, NULL);
process_scheduled_works(worker);
}
} while (keep_working(pool));
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
worker_set_flags(worker, WORKER_PREP);
sleep:
/*
* pool->lock is held and there's no work to process and no need to
* manage, sleep. Workers are woken up only while holding
* pool->lock or from local cpu, so setting the current state
* before releasing pool->lock is enough to prevent losing any
* event.
*/
worker_enter_idle(worker);
__set_current_state(TASK_INTERRUPTIBLE);
spin_unlock_irq(&pool->lock);
schedule();
goto woke_up;
}
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
/**
* rescuer_thread - the rescuer thread function
* @__rescuer: self
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
*
* Workqueue rescuer thread function. There's one rescuer for each
* workqueue which has WQ_MEM_RECLAIM set.
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
*
* Regular work processing on a pool may block trying to create a new
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
* worker which uses GFP_KERNEL allocation which has slight chance of
* developing into deadlock if some works currently on the same queue
* need to be processed to satisfy the GFP_KERNEL allocation. This is
* the problem rescuer solves.
*
* When such condition is possible, the pool summons rescuers of all
* workqueues which have works queued on the pool and let them process
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
* those works so that forward progress can be guaranteed.
*
* This should happen rarely.
*
* Return: 0
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
*/
static int rescuer_thread(void *__rescuer)
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
{
struct worker *rescuer = __rescuer;
struct workqueue_struct *wq = rescuer->rescue_wq;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
struct list_head *scheduled = &rescuer->scheduled;
bool should_stop;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
set_user_nice(current, RESCUER_NICE_LEVEL);
/*
* Mark rescuer as worker too. As WORKER_PREP is never cleared, it
* doesn't participate in concurrency management.
*/
rescuer->task->flags |= PF_WQ_WORKER;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
repeat:
set_current_state(TASK_INTERRUPTIBLE);
/*
* By the time the rescuer is requested to stop, the workqueue
* shouldn't have any work pending, but @wq->maydays may still have
* pwq(s) queued. This can happen by non-rescuer workers consuming
* all the work items before the rescuer got to them. Go through
* @wq->maydays processing before acting on should_stop so that the
* list is always empty on exit.
*/
should_stop = kthread_should_stop();
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
/* see whether any pwq is asking for help */
spin_lock_irq(&wq_mayday_lock);
while (!list_empty(&wq->maydays)) {
struct pool_workqueue *pwq = list_first_entry(&wq->maydays,
struct pool_workqueue, mayday_node);
struct worker_pool *pool = pwq->pool;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
struct work_struct *work, *n;
workqueue: implement lockup detector Workqueue stalls can happen from a variety of usage bugs such as missing WQ_MEM_RECLAIM flag or concurrency managed work item indefinitely staying RUNNING. These stalls can be extremely difficult to hunt down because the usual warning mechanisms can't detect workqueue stalls and the internal state is pretty opaque. To alleviate the situation, this patch implements workqueue lockup detector. It periodically monitors all worker_pools periodically and, if any pool failed to make forward progress longer than the threshold duration, triggers warning and dumps workqueue state as follows. BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 31s! Showing busy workqueues and worker pools: workqueue events: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=17/256 pending: monkey_wrench_fn, e1000_watchdog, cache_reap, vmstat_shepherd, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, cgroup_release_agent workqueue events_power_efficient: flags=0x80 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=2/256 pending: check_lifetime, neigh_periodic_work workqueue cgroup_pidlist_destroy: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/1 pending: cgroup_pidlist_destroy_work_fn ... The detection mechanism is controller through kernel parameter workqueue.watchdog_thresh and can be updated at runtime through the sysfs module parameter file. v2: Decoupled from softlockup control knobs. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Don Zickus <dzickus@redhat.com> Cc: Ulrich Obergfell <uobergfe@redhat.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Chris Mason <clm@fb.com> Cc: Andrew Morton <akpm@linux-foundation.org>
2015-12-08 16:28:04 +00:00
bool first = true;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
__set_current_state(TASK_RUNNING);
list_del_init(&pwq->mayday_node);
spin_unlock_irq(&wq_mayday_lock);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
worker_attach_to_pool(rescuer, pool);
spin_lock_irq(&pool->lock);
rescuer->pool = pool;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
/*
* Slurp in all works issued via this workqueue and
* process'em.
*/
WARN_ON_ONCE(!list_empty(scheduled));
workqueue: implement lockup detector Workqueue stalls can happen from a variety of usage bugs such as missing WQ_MEM_RECLAIM flag or concurrency managed work item indefinitely staying RUNNING. These stalls can be extremely difficult to hunt down because the usual warning mechanisms can't detect workqueue stalls and the internal state is pretty opaque. To alleviate the situation, this patch implements workqueue lockup detector. It periodically monitors all worker_pools periodically and, if any pool failed to make forward progress longer than the threshold duration, triggers warning and dumps workqueue state as follows. BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 31s! Showing busy workqueues and worker pools: workqueue events: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=17/256 pending: monkey_wrench_fn, e1000_watchdog, cache_reap, vmstat_shepherd, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, cgroup_release_agent workqueue events_power_efficient: flags=0x80 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=2/256 pending: check_lifetime, neigh_periodic_work workqueue cgroup_pidlist_destroy: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/1 pending: cgroup_pidlist_destroy_work_fn ... The detection mechanism is controller through kernel parameter workqueue.watchdog_thresh and can be updated at runtime through the sysfs module parameter file. v2: Decoupled from softlockup control knobs. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Don Zickus <dzickus@redhat.com> Cc: Ulrich Obergfell <uobergfe@redhat.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Chris Mason <clm@fb.com> Cc: Andrew Morton <akpm@linux-foundation.org>
2015-12-08 16:28:04 +00:00
list_for_each_entry_safe(work, n, &pool->worklist, entry) {
if (get_work_pwq(work) == pwq) {
if (first)
pool->watchdog_ts = jiffies;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
move_linked_works(work, scheduled, &n);
workqueue: implement lockup detector Workqueue stalls can happen from a variety of usage bugs such as missing WQ_MEM_RECLAIM flag or concurrency managed work item indefinitely staying RUNNING. These stalls can be extremely difficult to hunt down because the usual warning mechanisms can't detect workqueue stalls and the internal state is pretty opaque. To alleviate the situation, this patch implements workqueue lockup detector. It periodically monitors all worker_pools periodically and, if any pool failed to make forward progress longer than the threshold duration, triggers warning and dumps workqueue state as follows. BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 31s! Showing busy workqueues and worker pools: workqueue events: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=17/256 pending: monkey_wrench_fn, e1000_watchdog, cache_reap, vmstat_shepherd, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, cgroup_release_agent workqueue events_power_efficient: flags=0x80 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=2/256 pending: check_lifetime, neigh_periodic_work workqueue cgroup_pidlist_destroy: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/1 pending: cgroup_pidlist_destroy_work_fn ... The detection mechanism is controller through kernel parameter workqueue.watchdog_thresh and can be updated at runtime through the sysfs module parameter file. v2: Decoupled from softlockup control knobs. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Don Zickus <dzickus@redhat.com> Cc: Ulrich Obergfell <uobergfe@redhat.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Chris Mason <clm@fb.com> Cc: Andrew Morton <akpm@linux-foundation.org>
2015-12-08 16:28:04 +00:00
}
first = false;
}
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
workqueue: allow rescuer thread to do more work. When there is serious memory pressure, all workers in a pool could be blocked, and a new thread cannot be created because it requires memory allocation. In this situation a WQ_MEM_RECLAIM workqueue will wake up the rescuer thread to do some work. The rescuer will only handle requests that are already on ->worklist. If max_requests is 1, that means it will handle a single request. The rescuer will be woken again in 100ms to handle another max_requests requests. I've seen a machine (running a 3.0 based "enterprise" kernel) with thousands of requests queued for xfslogd, which has a max_requests of 1, and is needed for retiring all 'xfs' write requests. When one of the worker pools gets into this state, it progresses extremely slowly and possibly never recovers (only waited an hour or two). With this patch we leave a pool_workqueue on mayday list until it is clearly no longer in need of assistance. This allows all requests to be handled in a timely fashion. We keep each pool_workqueue on the mayday list until need_to_create_worker() is false, and no work for this workqueue is found in the pool. I have tested this in combination with a (hackish) patch which forces all work items to be handled by the rescuer thread. In that context it significantly improves performance. A similar patch for a 3.0 kernel significantly improved performance on a heavy work load. Thanks to Jan Kara for some design ideas, and to Dongsu Park for some comments and testing. tj: Inverted the lock order between wq_mayday_lock and pool->lock with a preceding patch and simplified this patch. Added comment and updated changelog accordingly. Dongsu spotted missing get_pwq() in the simplified code. Cc: Dongsu Park <dongsu.park@profitbricks.com> Cc: Jan Kara <jack@suse.cz> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: NeilBrown <neilb@suse.de> Signed-off-by: Tejun Heo <tj@kernel.org>
2014-12-08 17:39:16 +00:00
if (!list_empty(scheduled)) {
process_scheduled_works(rescuer);
/*
* The above execution of rescued work items could
* have created more to rescue through
* pwq_activate_first_delayed() or chained
* queueing. Let's put @pwq back on mayday list so
* that such back-to-back work items, which may be
* being used to relieve memory pressure, don't
* incur MAYDAY_INTERVAL delay inbetween.
*/
if (need_to_create_worker(pool)) {
spin_lock(&wq_mayday_lock);
get_pwq(pwq);
list_move_tail(&pwq->mayday_node, &wq->maydays);
spin_unlock(&wq_mayday_lock);
}
}
/*
* Put the reference grabbed by send_mayday(). @pool won't
* go away while we're still attached to it.
*/
put_pwq(pwq);
/*
* Leave this pool. If need_more_worker() is %true, notify a
* regular worker; otherwise, we end up with 0 concurrency
* and stalling the execution.
*/
if (need_more_worker(pool))
wake_up_worker(pool);
rescuer->pool = NULL;
spin_unlock_irq(&pool->lock);
worker_detach_from_pool(rescuer, pool);
spin_lock_irq(&wq_mayday_lock);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
}
spin_unlock_irq(&wq_mayday_lock);
if (should_stop) {
__set_current_state(TASK_RUNNING);
rescuer->task->flags &= ~PF_WQ_WORKER;
return 0;
}
/* rescuers should never participate in concurrency management */
WARN_ON_ONCE(!(rescuer->flags & WORKER_NOT_RUNNING));
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
schedule();
goto repeat;
}
/**
* check_flush_dependency - check for flush dependency sanity
* @target_wq: workqueue being flushed
* @target_work: work item being flushed (NULL for workqueue flushes)
*
* %current is trying to flush the whole @target_wq or @target_work on it.
* If @target_wq doesn't have %WQ_MEM_RECLAIM, verify that %current is not
* reclaiming memory or running on a workqueue which doesn't have
* %WQ_MEM_RECLAIM as that can break forward-progress guarantee leading to
* a deadlock.
*/
static void check_flush_dependency(struct workqueue_struct *target_wq,
struct work_struct *target_work)
{
work_func_t target_func = target_work ? target_work->func : NULL;
struct worker *worker;
if (target_wq->flags & WQ_MEM_RECLAIM)
return;
worker = current_wq_worker();
WARN_ONCE(current->flags & PF_MEMALLOC,
"workqueue: PF_MEMALLOC task %d(%s) is flushing !WQ_MEM_RECLAIM %s:%pf",
current->pid, current->comm, target_wq->name, target_func);
workqueue: skip flush dependency checks for legacy workqueues fca839c00a12 ("workqueue: warn if memory reclaim tries to flush !WQ_MEM_RECLAIM workqueue") implemented flush dependency warning which triggers if a PF_MEMALLOC task or WQ_MEM_RECLAIM workqueue tries to flush a !WQ_MEM_RECLAIM workquee. This assumes that workqueues marked with WQ_MEM_RECLAIM sit in memory reclaim path and making it depend on something which may need more memory to make forward progress can lead to deadlocks. Unfortunately, workqueues created with the legacy create*_workqueue() interface always have WQ_MEM_RECLAIM regardless of whether they are depended upon memory reclaim or not. These spurious WQ_MEM_RECLAIM markings cause spurious triggering of the flush dependency checks. WARNING: CPU: 0 PID: 6 at kernel/workqueue.c:2361 check_flush_dependency+0x138/0x144() workqueue: WQ_MEM_RECLAIM deferwq:deferred_probe_work_func is flushing !WQ_MEM_RECLAIM events:lru_add_drain_per_cpu ... Workqueue: deferwq deferred_probe_work_func [<c0017acc>] (unwind_backtrace) from [<c0013134>] (show_stack+0x10/0x14) [<c0013134>] (show_stack) from [<c0245f18>] (dump_stack+0x94/0xd4) [<c0245f18>] (dump_stack) from [<c0026f9c>] (warn_slowpath_common+0x80/0xb0) [<c0026f9c>] (warn_slowpath_common) from [<c0026ffc>] (warn_slowpath_fmt+0x30/0x40) [<c0026ffc>] (warn_slowpath_fmt) from [<c00390b8>] (check_flush_dependency+0x138/0x144) [<c00390b8>] (check_flush_dependency) from [<c0039ca0>] (flush_work+0x50/0x15c) [<c0039ca0>] (flush_work) from [<c00c51b0>] (lru_add_drain_all+0x130/0x180) [<c00c51b0>] (lru_add_drain_all) from [<c00f728c>] (migrate_prep+0x8/0x10) [<c00f728c>] (migrate_prep) from [<c00bfbc4>] (alloc_contig_range+0xd8/0x338) [<c00bfbc4>] (alloc_contig_range) from [<c00f8f18>] (cma_alloc+0xe0/0x1ac) [<c00f8f18>] (cma_alloc) from [<c001cac4>] (__alloc_from_contiguous+0x38/0xd8) [<c001cac4>] (__alloc_from_contiguous) from [<c001ceb4>] (__dma_alloc+0x240/0x278) [<c001ceb4>] (__dma_alloc) from [<c001cf78>] (arm_dma_alloc+0x54/0x5c) [<c001cf78>] (arm_dma_alloc) from [<c0355ea4>] (dmam_alloc_coherent+0xc0/0xec) [<c0355ea4>] (dmam_alloc_coherent) from [<c039cc4c>] (ahci_port_start+0x150/0x1dc) [<c039cc4c>] (ahci_port_start) from [<c0384734>] (ata_host_start.part.3+0xc8/0x1c8) [<c0384734>] (ata_host_start.part.3) from [<c03898dc>] (ata_host_activate+0x50/0x148) [<c03898dc>] (ata_host_activate) from [<c039d558>] (ahci_host_activate+0x44/0x114) [<c039d558>] (ahci_host_activate) from [<c039f05c>] (ahci_platform_init_host+0x1d8/0x3c8) [<c039f05c>] (ahci_platform_init_host) from [<c039e6bc>] (tegra_ahci_probe+0x448/0x4e8) [<c039e6bc>] (tegra_ahci_probe) from [<c0347058>] (platform_drv_probe+0x50/0xac) [<c0347058>] (platform_drv_probe) from [<c03458cc>] (driver_probe_device+0x214/0x2c0) [<c03458cc>] (driver_probe_device) from [<c0343cc0>] (bus_for_each_drv+0x60/0x94) [<c0343cc0>] (bus_for_each_drv) from [<c03455d8>] (__device_attach+0xb0/0x114) [<c03455d8>] (__device_attach) from [<c0344ab8>] (bus_probe_device+0x84/0x8c) [<c0344ab8>] (bus_probe_device) from [<c0344f48>] (deferred_probe_work_func+0x68/0x98) [<c0344f48>] (deferred_probe_work_func) from [<c003b738>] (process_one_work+0x120/0x3f8) [<c003b738>] (process_one_work) from [<c003ba48>] (worker_thread+0x38/0x55c) [<c003ba48>] (worker_thread) from [<c0040f14>] (kthread+0xdc/0xf4) [<c0040f14>] (kthread) from [<c000f778>] (ret_from_fork+0x14/0x3c) Fix it by marking workqueues created via create*_workqueue() with __WQ_LEGACY and disabling flush dependency checks on them. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-and-tested-by: Thierry Reding <thierry.reding@gmail.com> Link: http://lkml.kernel.org/g/20160126173843.GA11115@ulmo.nvidia.com Fixes: fca839c00a12 ("workqueue: warn if memory reclaim tries to flush !WQ_MEM_RECLAIM workqueue")
2016-01-29 10:59:46 +00:00
WARN_ONCE(worker && ((worker->current_pwq->wq->flags &
(WQ_MEM_RECLAIM | __WQ_LEGACY)) == WQ_MEM_RECLAIM),
"workqueue: WQ_MEM_RECLAIM %s:%pf is flushing !WQ_MEM_RECLAIM %s:%pf",
worker->current_pwq->wq->name, worker->current_func,
target_wq->name, target_func);
}
struct wq_barrier {
struct work_struct work;
struct completion done;
struct task_struct *task; /* purely informational */
};
static void wq_barrier_func(struct work_struct *work)
{
struct wq_barrier *barr = container_of(work, struct wq_barrier, work);
complete(&barr->done);
}
/**
* insert_wq_barrier - insert a barrier work
* @pwq: pwq to insert barrier into
* @barr: wq_barrier to insert
* @target: target work to attach @barr to
* @worker: worker currently executing @target, NULL if @target is not executing
*
* @barr is linked to @target such that @barr is completed only after
* @target finishes execution. Please note that the ordering
* guarantee is observed only with respect to @target and on the local
* cpu.
*
* Currently, a queued barrier can't be canceled. This is because
* try_to_grab_pending() can't determine whether the work to be
* grabbed is at the head of the queue and thus can't clear LINKED
* flag of the previous work while there must be a valid next work
* after a work with LINKED flag set.
*
* Note that when @worker is non-NULL, @target may be modified
* underneath us, so we can't reliably determine pwq from @target.
*
* CONTEXT:
* spin_lock_irq(pool->lock).
*/
static void insert_wq_barrier(struct pool_workqueue *pwq,
struct wq_barrier *barr,
struct work_struct *target, struct worker *worker)
{
struct list_head *head;
unsigned int linked = 0;
/*
* debugobject calls are safe here even with pool->lock locked
* as we know for sure that this will not trigger any of the
* checks and call back into the fixup functions where we
* might deadlock.
*/
INIT_WORK_ONSTACK(&barr->work, wq_barrier_func);
__set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&barr->work));
init_completion(&barr->done);
barr->task = current;
/*
* If @target is currently being executed, schedule the
* barrier to the worker; otherwise, put it after @target.
*/
if (worker)
head = worker->scheduled.next;
else {
unsigned long *bits = work_data_bits(target);
head = target->entry.next;
/* there can already be other linked works, inherit and set */
linked = *bits & WORK_STRUCT_LINKED;
__set_bit(WORK_STRUCT_LINKED_BIT, bits);
}
debug_work_activate(&barr->work);
insert_work(pwq, &barr->work, head,
work_color_to_flags(WORK_NO_COLOR) | linked);
}
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
/**
* flush_workqueue_prep_pwqs - prepare pwqs for workqueue flushing
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
* @wq: workqueue being flushed
* @flush_color: new flush color, < 0 for no-op
* @work_color: new work color, < 0 for no-op
*
* Prepare pwqs for workqueue flushing.
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
*
* If @flush_color is non-negative, flush_color on all pwqs should be
* -1. If no pwq has in-flight commands at the specified color, all
* pwq->flush_color's stay at -1 and %false is returned. If any pwq
* has in flight commands, its pwq->flush_color is set to
* @flush_color, @wq->nr_pwqs_to_flush is updated accordingly, pwq
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
* wakeup logic is armed and %true is returned.
*
* The caller should have initialized @wq->first_flusher prior to
* calling this function with non-negative @flush_color. If
* @flush_color is negative, no flush color update is done and %false
* is returned.
*
* If @work_color is non-negative, all pwqs should have the same
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
* work_color which is previous to @work_color and all will be
* advanced to @work_color.
*
* CONTEXT:
* mutex_lock(wq->mutex).
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
*
* Return:
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
* %true if @flush_color >= 0 and there's something to flush. %false
* otherwise.
*/
static bool flush_workqueue_prep_pwqs(struct workqueue_struct *wq,
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
int flush_color, int work_color)
{
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
bool wait = false;
struct pool_workqueue *pwq;
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
if (flush_color >= 0) {
WARN_ON_ONCE(atomic_read(&wq->nr_pwqs_to_flush));
atomic_set(&wq->nr_pwqs_to_flush, 1);
}
for_each_pwq(pwq, wq) {
struct worker_pool *pool = pwq->pool;
spin_lock_irq(&pool->lock);
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
if (flush_color >= 0) {
WARN_ON_ONCE(pwq->flush_color != -1);
if (pwq->nr_in_flight[flush_color]) {
pwq->flush_color = flush_color;
atomic_inc(&wq->nr_pwqs_to_flush);
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
wait = true;
}
}
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
if (work_color >= 0) {
WARN_ON_ONCE(work_color != work_next_color(pwq->work_color));
pwq->work_color = work_color;
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
}
spin_unlock_irq(&pool->lock);
}
if (flush_color >= 0 && atomic_dec_and_test(&wq->nr_pwqs_to_flush))
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
complete(&wq->first_flusher->done);
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
return wait;
}
/**
* flush_workqueue - ensure that any scheduled work has run to completion.
* @wq: workqueue to flush
*
* This function sleeps until all work items which were queued on entry
* have finished execution, but it is not livelocked by new incoming ones.
*/
void flush_workqueue(struct workqueue_struct *wq)
{
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
struct wq_flusher this_flusher = {
.list = LIST_HEAD_INIT(this_flusher.list),
.flush_color = -1,
.done = COMPLETION_INITIALIZER_ONSTACK(this_flusher.done),
};
int next_color;
workqueue: make workqueue available early during boot Workqueue is currently initialized in an early init call; however, there are cases where early boot code has to be split and reordered to come after workqueue initialization or the same code path which makes use of workqueues is used both before workqueue initailization and after. The latter cases have to gate workqueue usages with keventd_up() tests, which is nasty and easy to get wrong. Workqueue usages have become widespread and it'd be a lot more convenient if it can be used very early from boot. This patch splits workqueue initialization into two steps. workqueue_init_early() which sets up the basic data structures so that workqueues can be created and work items queued, and workqueue_init() which actually brings up workqueues online and starts executing queued work items. The former step can be done very early during boot once memory allocation, cpumasks and idr are initialized. The latter right after kthreads become available. This allows work item queueing and canceling from very early boot which is what most of these use cases want. * As systemd_wq being initialized doesn't indicate that workqueue is fully online anymore, update keventd_up() to test wq_online instead. The follow-up patches will get rid of all its usages and the function itself. * Flushing doesn't make sense before workqueue is fully initialized. The flush functions trigger WARN and return immediately before fully online. * Work items are never in-flight before fully online. Canceling can always succeed by skipping the flush step. * Some code paths can no longer assume to be called with irq enabled as irq is disabled during early boot. Use irqsave/restore operations instead. v2: Watchdog init, which requires timer to be running, moved from workqueue_init_early() to workqueue_init(). Signed-off-by: Tejun Heo <tj@kernel.org> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/CA+55aFx0vPuMuxn00rBSM192n-Du5uxy+4AvKa0SBSOVJeuCGg@mail.gmail.com
2016-09-16 19:49:32 +00:00
if (WARN_ON(!wq_online))
return;
lock_map_acquire(&wq->lockdep_map);
lock_map_release(&wq->lockdep_map);
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
mutex_lock(&wq->mutex);
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
/*
* Start-to-wait phase
*/
next_color = work_next_color(wq->work_color);
if (next_color != wq->flush_color) {
/*
* Color space is not full. The current work_color
* becomes our flush_color and work_color is advanced
* by one.
*/
WARN_ON_ONCE(!list_empty(&wq->flusher_overflow));
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
this_flusher.flush_color = wq->work_color;
wq->work_color = next_color;
if (!wq->first_flusher) {
/* no flush in progress, become the first flusher */
WARN_ON_ONCE(wq->flush_color != this_flusher.flush_color);
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
wq->first_flusher = &this_flusher;
if (!flush_workqueue_prep_pwqs(wq, wq->flush_color,
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
wq->work_color)) {
/* nothing to flush, done */
wq->flush_color = next_color;
wq->first_flusher = NULL;
goto out_unlock;
}
} else {
/* wait in queue */
WARN_ON_ONCE(wq->flush_color == this_flusher.flush_color);
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
list_add_tail(&this_flusher.list, &wq->flusher_queue);
flush_workqueue_prep_pwqs(wq, -1, wq->work_color);
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
}
} else {
/*
* Oops, color space is full, wait on overflow queue.
* The next flush completion will assign us
* flush_color and transfer to flusher_queue.
*/
list_add_tail(&this_flusher.list, &wq->flusher_overflow);
}
check_flush_dependency(wq, NULL);
mutex_unlock(&wq->mutex);
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
wait_for_completion(&this_flusher.done);
/*
* Wake-up-and-cascade phase
*
* First flushers are responsible for cascading flushes and
* handling overflow. Non-first flushers can simply return.
*/
if (wq->first_flusher != &this_flusher)
return;
mutex_lock(&wq->mutex);
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
/* we might have raced, check again with mutex held */
if (wq->first_flusher != &this_flusher)
goto out_unlock;
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
wq->first_flusher = NULL;
WARN_ON_ONCE(!list_empty(&this_flusher.list));
WARN_ON_ONCE(wq->flush_color != this_flusher.flush_color);
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
while (true) {
struct wq_flusher *next, *tmp;
/* complete all the flushers sharing the current flush color */
list_for_each_entry_safe(next, tmp, &wq->flusher_queue, list) {
if (next->flush_color != wq->flush_color)
break;
list_del_init(&next->list);
complete(&next->done);
}
WARN_ON_ONCE(!list_empty(&wq->flusher_overflow) &&
wq->flush_color != work_next_color(wq->work_color));
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
/* this flush_color is finished, advance by one */
wq->flush_color = work_next_color(wq->flush_color);
/* one color has been freed, handle overflow queue */
if (!list_empty(&wq->flusher_overflow)) {
/*
* Assign the same color to all overflowed
* flushers, advance work_color and append to
* flusher_queue. This is the start-to-wait
* phase for these overflowed flushers.
*/
list_for_each_entry(tmp, &wq->flusher_overflow, list)
tmp->flush_color = wq->work_color;
wq->work_color = work_next_color(wq->work_color);
list_splice_tail_init(&wq->flusher_overflow,
&wq->flusher_queue);
flush_workqueue_prep_pwqs(wq, -1, wq->work_color);
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
}
if (list_empty(&wq->flusher_queue)) {
WARN_ON_ONCE(wq->flush_color != wq->work_color);
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
break;
}
/*
* Need to flush more colors. Make the next flusher
* the new first flusher and arm pwqs.
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
*/
WARN_ON_ONCE(wq->flush_color == wq->work_color);
WARN_ON_ONCE(wq->flush_color != next->flush_color);
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
list_del_init(&next->list);
wq->first_flusher = next;
if (flush_workqueue_prep_pwqs(wq, wq->flush_color, -1))
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
break;
/*
* Meh... this color is already done, clear first
* flusher and repeat cascading.
*/
wq->first_flusher = NULL;
}
out_unlock:
mutex_unlock(&wq->mutex);
}
EXPORT_SYMBOL(flush_workqueue);
/**
* drain_workqueue - drain a workqueue
* @wq: workqueue to drain
*
* Wait until the workqueue becomes empty. While draining is in progress,
* only chain queueing is allowed. IOW, only currently pending or running
* work items on @wq can queue further work items on it. @wq is flushed
* repeatedly until it becomes empty. The number of flushing is determined
* by the depth of chaining and should be relatively short. Whine if it
* takes too long.
*/
void drain_workqueue(struct workqueue_struct *wq)
{
unsigned int flush_cnt = 0;
struct pool_workqueue *pwq;
/*
* __queue_work() needs to test whether there are drainers, is much
* hotter than drain_workqueue() and already looks at @wq->flags.
* Use __WQ_DRAINING so that queue doesn't have to check nr_drainers.
*/
mutex_lock(&wq->mutex);
if (!wq->nr_drainers++)
wq->flags |= __WQ_DRAINING;
mutex_unlock(&wq->mutex);
reflush:
flush_workqueue(wq);
mutex_lock(&wq->mutex);
for_each_pwq(pwq, wq) {
bool drained;
spin_lock_irq(&pwq->pool->lock);
drained = !pwq->nr_active && list_empty(&pwq->delayed_works);
spin_unlock_irq(&pwq->pool->lock);
if (drained)
continue;
if (++flush_cnt == 10 ||
(flush_cnt % 100 == 0 && flush_cnt <= 1000))
pr_warn("workqueue %s: drain_workqueue() isn't complete after %u tries\n",
wq->name, flush_cnt);
mutex_unlock(&wq->mutex);
goto reflush;
}
if (!--wq->nr_drainers)
wq->flags &= ~__WQ_DRAINING;
mutex_unlock(&wq->mutex);
}
EXPORT_SYMBOL_GPL(drain_workqueue);
static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr)
{
struct worker *worker = NULL;
struct worker_pool *pool;
struct pool_workqueue *pwq;
might_sleep();
local_irq_disable();
pool = get_work_pool(work);
if (!pool) {
local_irq_enable();
return false;
}
spin_lock(&pool->lock);
workqueue: simplify is-work-item-queued-here test Currently, determining whether a work item is queued on a locked pool involves somewhat convoluted memory barrier dancing. It goes like the following. * When a work item is queued on a pool, work->data is updated before work->entry is linked to the pending list with a wmb() inbetween. * When trying to determine whether a work item is currently queued on a pool pointed to by work->data, it locks the pool and looks at work->entry. If work->entry is linked, we then do rmb() and then check whether work->data points to the current pool. This works because, work->data can only point to a pool if it currently is or were on the pool and, * If it currently is on the pool, the tests would obviously succeed. * It it left the pool, its work->entry was cleared under pool->lock, so if we're seeing non-empty work->entry, it has to be from the work item being linked on another pool. Because work->data is updated before work->entry is linked with wmb() inbetween, work->data update from another pool is guaranteed to be visible if we do rmb() after seeing non-empty work->entry. So, we either see empty work->entry or we see updated work->data pointin to another pool. While this works, it's convoluted, to put it mildly. With recent updates, it's now guaranteed that work->data points to cwq only while the work item is queued and that updating work->data to point to cwq or back to pool is done under pool->lock, so we can simply test whether work->data points to cwq which is associated with the currently locked pool instead of the convoluted memory barrier dancing. This patch replaces the memory barrier based "are you still here, really?" test with much simpler "does work->data points to me?" test - if work->data points to a cwq which is associated with the currently locked pool, the work item is guaranteed to be queued on the pool as work->data can start and stop pointing to such cwq only under pool->lock and the start and stop coincide with queue and dequeue. tj: Rewrote the comments and description. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2013-02-07 02:04:53 +00:00
/* see the comment in try_to_grab_pending() with the same code */
pwq = get_work_pwq(work);
if (pwq) {
if (unlikely(pwq->pool != pool))
goto already_gone;
} else {
worker = find_worker_executing_work(pool, work);
if (!worker)
goto already_gone;
pwq = worker->current_pwq;
}
check_flush_dependency(pwq->wq, work);
insert_wq_barrier(pwq, barr, work, worker);
spin_unlock_irq(&pool->lock);
/*
* If @max_active is 1 or rescuer is in use, flushing another work
* item on the same workqueue may lead to deadlock. Make sure the
* flusher is not running on the same workqueue by verifying write
* access.
*/
if (pwq->wq->saved_max_active == 1 || pwq->wq->rescuer)
lock_map_acquire(&pwq->wq->lockdep_map);
else
lock_map_acquire_read(&pwq->wq->lockdep_map);
lock_map_release(&pwq->wq->lockdep_map);
return true;
already_gone:
spin_unlock_irq(&pool->lock);
return false;
}
/**
* flush_work - wait for a work to finish executing the last queueing instance
* @work: the work to flush
*
* Wait until @work has finished execution. @work is guaranteed to be idle
* on return if it hasn't been requeued since flush started.
*
* Return:
* %true if flush_work() waited for the work to finish execution,
* %false if it was already idle.
*/
bool flush_work(struct work_struct *work)
{
struct wq_barrier barr;
workqueue: make workqueue available early during boot Workqueue is currently initialized in an early init call; however, there are cases where early boot code has to be split and reordered to come after workqueue initialization or the same code path which makes use of workqueues is used both before workqueue initailization and after. The latter cases have to gate workqueue usages with keventd_up() tests, which is nasty and easy to get wrong. Workqueue usages have become widespread and it'd be a lot more convenient if it can be used very early from boot. This patch splits workqueue initialization into two steps. workqueue_init_early() which sets up the basic data structures so that workqueues can be created and work items queued, and workqueue_init() which actually brings up workqueues online and starts executing queued work items. The former step can be done very early during boot once memory allocation, cpumasks and idr are initialized. The latter right after kthreads become available. This allows work item queueing and canceling from very early boot which is what most of these use cases want. * As systemd_wq being initialized doesn't indicate that workqueue is fully online anymore, update keventd_up() to test wq_online instead. The follow-up patches will get rid of all its usages and the function itself. * Flushing doesn't make sense before workqueue is fully initialized. The flush functions trigger WARN and return immediately before fully online. * Work items are never in-flight before fully online. Canceling can always succeed by skipping the flush step. * Some code paths can no longer assume to be called with irq enabled as irq is disabled during early boot. Use irqsave/restore operations instead. v2: Watchdog init, which requires timer to be running, moved from workqueue_init_early() to workqueue_init(). Signed-off-by: Tejun Heo <tj@kernel.org> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/CA+55aFx0vPuMuxn00rBSM192n-Du5uxy+4AvKa0SBSOVJeuCGg@mail.gmail.com
2016-09-16 19:49:32 +00:00
if (WARN_ON(!wq_online))
return false;
lock_map_acquire(&work->lockdep_map);
lock_map_release(&work->lockdep_map);
if (start_flush_work(work, &barr)) {
wait_for_completion(&barr.done);
destroy_work_on_stack(&barr.work);
return true;
} else {
return false;
}
make cancel_rearming_delayed_work() reliable Thanks to Jarek Poplawski for the ideas and for spotting the bug in the initial draft patch. cancel_rearming_delayed_work() currently has many limitations, because it requires that dwork always re-arms itself via queue_delayed_work(). So it hangs forever if dwork doesn't do this, or cancel_rearming_delayed_work/ cancel_delayed_work was already called. It uses flush_workqueue() in a loop, so it can't be used if workqueue was freezed, and it is potentially live- lockable on busy system if delay is small. With this patch cancel_rearming_delayed_work() doesn't make any assumptions about dwork, it can re-arm itself via queue_delayed_work(), or queue_work(), or do nothing. As a "side effect", cancel_work_sync() was changed to handle re-arming works as well. Disadvantages: - this patch adds wmb() to insert_work(). - slowdowns the fast path (when del_timer() succeeds on entry) of cancel_rearming_delayed_work(), because wait_on_work() is called unconditionally. In that case, compared to the old version, we are doing "unneeded" lock/unlock for each online CPU. On the other hand, this means we don't need to use cancel_work_sync() after cancel_rearming_delayed_work(). - complicates the code (.text grows by 130 bytes). [akpm@linux-foundation.org: fix speling] Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: David Chinner <dgc@sgi.com> Cc: David Howells <dhowells@redhat.com> Cc: Gautham Shenoy <ego@in.ibm.com> Acked-by: Jarek Poplawski <jarkao2@o2.pl> Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-09 09:34:46 +00:00
}
EXPORT_SYMBOL_GPL(flush_work);
make cancel_rearming_delayed_work() reliable Thanks to Jarek Poplawski for the ideas and for spotting the bug in the initial draft patch. cancel_rearming_delayed_work() currently has many limitations, because it requires that dwork always re-arms itself via queue_delayed_work(). So it hangs forever if dwork doesn't do this, or cancel_rearming_delayed_work/ cancel_delayed_work was already called. It uses flush_workqueue() in a loop, so it can't be used if workqueue was freezed, and it is potentially live- lockable on busy system if delay is small. With this patch cancel_rearming_delayed_work() doesn't make any assumptions about dwork, it can re-arm itself via queue_delayed_work(), or queue_work(), or do nothing. As a "side effect", cancel_work_sync() was changed to handle re-arming works as well. Disadvantages: - this patch adds wmb() to insert_work(). - slowdowns the fast path (when del_timer() succeeds on entry) of cancel_rearming_delayed_work(), because wait_on_work() is called unconditionally. In that case, compared to the old version, we are doing "unneeded" lock/unlock for each online CPU. On the other hand, this means we don't need to use cancel_work_sync() after cancel_rearming_delayed_work(). - complicates the code (.text grows by 130 bytes). [akpm@linux-foundation.org: fix speling] Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: David Chinner <dgc@sgi.com> Cc: David Howells <dhowells@redhat.com> Cc: Gautham Shenoy <ego@in.ibm.com> Acked-by: Jarek Poplawski <jarkao2@o2.pl> Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-09 09:34:46 +00:00
workqueue: fix hang involving racing cancel[_delayed]_work_sync()'s for PREEMPT_NONE cancel[_delayed]_work_sync() are implemented using __cancel_work_timer() which grabs the PENDING bit using try_to_grab_pending() and then flushes the work item with PENDING set to prevent the on-going execution of the work item from requeueing itself. try_to_grab_pending() can always grab PENDING bit without blocking except when someone else is doing the above flushing during cancelation. In that case, try_to_grab_pending() returns -ENOENT. In this case, __cancel_work_timer() currently invokes flush_work(). The assumption is that the completion of the work item is what the other canceling task would be waiting for too and thus waiting for the same condition and retrying should allow forward progress without excessive busy looping Unfortunately, this doesn't work if preemption is disabled or the latter task has real time priority. Let's say task A just got woken up from flush_work() by the completion of the target work item. If, before task A starts executing, task B gets scheduled and invokes __cancel_work_timer() on the same work item, its try_to_grab_pending() will return -ENOENT as the work item is still being canceled by task A and flush_work() will also immediately return false as the work item is no longer executing. This puts task B in a busy loop possibly preventing task A from executing and clearing the canceling state on the work item leading to a hang. task A task B worker executing work __cancel_work_timer() try_to_grab_pending() set work CANCELING flush_work() block for work completion completion, wakes up A __cancel_work_timer() while (forever) { try_to_grab_pending() -ENOENT as work is being canceled flush_work() false as work is no longer executing } This patch removes the possible hang by updating __cancel_work_timer() to explicitly wait for clearing of CANCELING rather than invoking flush_work() after try_to_grab_pending() fails with -ENOENT. Link: http://lkml.kernel.org/g/20150206171156.GA8942@axis.com v3: bit_waitqueue() can't be used for work items defined in vmalloc area. Switched to custom wake function which matches the target work item and exclusive wait and wakeup. v2: v1 used wake_up() on bit_waitqueue() which leads to NULL deref if the target bit waitqueue has wait_bit_queue's on it. Use DEFINE_WAIT_BIT() and __wake_up_bit() instead. Reported by Tomeu Vizoso. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Rabin Vincent <rabin.vincent@axis.com> Cc: Tomeu Vizoso <tomeu.vizoso@gmail.com> Cc: stable@vger.kernel.org Tested-by: Jesper Nilsson <jesper.nilsson@axis.com> Tested-by: Rabin Vincent <rabin.vincent@axis.com>
2015-03-05 13:04:13 +00:00
struct cwt_wait {
wait_queue_t wait;
struct work_struct *work;
};
static int cwt_wakefn(wait_queue_t *wait, unsigned mode, int sync, void *key)
{
struct cwt_wait *cwait = container_of(wait, struct cwt_wait, wait);
if (cwait->work != key)
return 0;
return autoremove_wake_function(wait, mode, sync, key);
}
static bool __cancel_work_timer(struct work_struct *work, bool is_dwork)
{
workqueue: fix hang involving racing cancel[_delayed]_work_sync()'s for PREEMPT_NONE cancel[_delayed]_work_sync() are implemented using __cancel_work_timer() which grabs the PENDING bit using try_to_grab_pending() and then flushes the work item with PENDING set to prevent the on-going execution of the work item from requeueing itself. try_to_grab_pending() can always grab PENDING bit without blocking except when someone else is doing the above flushing during cancelation. In that case, try_to_grab_pending() returns -ENOENT. In this case, __cancel_work_timer() currently invokes flush_work(). The assumption is that the completion of the work item is what the other canceling task would be waiting for too and thus waiting for the same condition and retrying should allow forward progress without excessive busy looping Unfortunately, this doesn't work if preemption is disabled or the latter task has real time priority. Let's say task A just got woken up from flush_work() by the completion of the target work item. If, before task A starts executing, task B gets scheduled and invokes __cancel_work_timer() on the same work item, its try_to_grab_pending() will return -ENOENT as the work item is still being canceled by task A and flush_work() will also immediately return false as the work item is no longer executing. This puts task B in a busy loop possibly preventing task A from executing and clearing the canceling state on the work item leading to a hang. task A task B worker executing work __cancel_work_timer() try_to_grab_pending() set work CANCELING flush_work() block for work completion completion, wakes up A __cancel_work_timer() while (forever) { try_to_grab_pending() -ENOENT as work is being canceled flush_work() false as work is no longer executing } This patch removes the possible hang by updating __cancel_work_timer() to explicitly wait for clearing of CANCELING rather than invoking flush_work() after try_to_grab_pending() fails with -ENOENT. Link: http://lkml.kernel.org/g/20150206171156.GA8942@axis.com v3: bit_waitqueue() can't be used for work items defined in vmalloc area. Switched to custom wake function which matches the target work item and exclusive wait and wakeup. v2: v1 used wake_up() on bit_waitqueue() which leads to NULL deref if the target bit waitqueue has wait_bit_queue's on it. Use DEFINE_WAIT_BIT() and __wake_up_bit() instead. Reported by Tomeu Vizoso. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Rabin Vincent <rabin.vincent@axis.com> Cc: Tomeu Vizoso <tomeu.vizoso@gmail.com> Cc: stable@vger.kernel.org Tested-by: Jesper Nilsson <jesper.nilsson@axis.com> Tested-by: Rabin Vincent <rabin.vincent@axis.com>
2015-03-05 13:04:13 +00:00
static DECLARE_WAIT_QUEUE_HEAD(cancel_waitq);
workqueue: mark a work item being canceled as such There can be two reasons try_to_grab_pending() can fail with -EAGAIN. One is when someone else is queueing or deqeueing the work item. With the previous patches, it is guaranteed that PENDING and queued state will soon agree making it safe to busy-retry in this case. The other is if multiple __cancel_work_timer() invocations are racing one another. __cancel_work_timer() grabs PENDING and then waits for running instances of the target work item on all CPUs while holding PENDING and !queued. try_to_grab_pending() invoked from another task will keep returning -EAGAIN while the current owner is waiting. Not distinguishing the two cases is okay because __cancel_work_timer() is the only user of try_to_grab_pending() and it invokes wait_on_work() whenever grabbing fails. For the first case, busy looping should be fine but wait_on_work() doesn't cause any critical problem. For the latter case, the new contender usually waits for the same condition as the current owner, so no unnecessarily extended busy-looping happens. Combined, these make __cancel_work_timer() technically correct even without irq protection while grabbing PENDING or distinguishing the two different cases. While the current code is technically correct, not distinguishing the two cases makes it difficult to use try_to_grab_pending() for other purposes than canceling because it's impossible to tell whether it's safe to busy-retry grabbing. This patch adds a mechanism to mark a work item being canceled. try_to_grab_pending() now disables irq on success and returns -EAGAIN to indicate that grabbing failed but PENDING and queued states are gonna agree soon and it's safe to busy-loop. It returns -ENOENT if the work item is being canceled and it may stay PENDING && !queued for arbitrary amount of time. __cancel_work_timer() is modified to mark the work canceling with WORK_OFFQ_CANCELING after grabbing PENDING, thus making try_to_grab_pending() fail with -ENOENT instead of -EAGAIN. Also, it invokes wait_on_work() iff grabbing failed with -ENOENT. This isn't necessary for correctness but makes it consistent with other future users of try_to_grab_pending(). v2: try_to_grab_pending() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Updated so that try_to_grab_pending() disables irq on success rather than requiring preemption disabled by the caller. This makes busy-looping easier and will allow try_to_grap_pending() to be used from bh/irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:46 +00:00
unsigned long flags;
int ret;
do {
workqueue: mark a work item being canceled as such There can be two reasons try_to_grab_pending() can fail with -EAGAIN. One is when someone else is queueing or deqeueing the work item. With the previous patches, it is guaranteed that PENDING and queued state will soon agree making it safe to busy-retry in this case. The other is if multiple __cancel_work_timer() invocations are racing one another. __cancel_work_timer() grabs PENDING and then waits for running instances of the target work item on all CPUs while holding PENDING and !queued. try_to_grab_pending() invoked from another task will keep returning -EAGAIN while the current owner is waiting. Not distinguishing the two cases is okay because __cancel_work_timer() is the only user of try_to_grab_pending() and it invokes wait_on_work() whenever grabbing fails. For the first case, busy looping should be fine but wait_on_work() doesn't cause any critical problem. For the latter case, the new contender usually waits for the same condition as the current owner, so no unnecessarily extended busy-looping happens. Combined, these make __cancel_work_timer() technically correct even without irq protection while grabbing PENDING or distinguishing the two different cases. While the current code is technically correct, not distinguishing the two cases makes it difficult to use try_to_grab_pending() for other purposes than canceling because it's impossible to tell whether it's safe to busy-retry grabbing. This patch adds a mechanism to mark a work item being canceled. try_to_grab_pending() now disables irq on success and returns -EAGAIN to indicate that grabbing failed but PENDING and queued states are gonna agree soon and it's safe to busy-loop. It returns -ENOENT if the work item is being canceled and it may stay PENDING && !queued for arbitrary amount of time. __cancel_work_timer() is modified to mark the work canceling with WORK_OFFQ_CANCELING after grabbing PENDING, thus making try_to_grab_pending() fail with -ENOENT instead of -EAGAIN. Also, it invokes wait_on_work() iff grabbing failed with -ENOENT. This isn't necessary for correctness but makes it consistent with other future users of try_to_grab_pending(). v2: try_to_grab_pending() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Updated so that try_to_grab_pending() disables irq on success rather than requiring preemption disabled by the caller. This makes busy-looping easier and will allow try_to_grap_pending() to be used from bh/irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:46 +00:00
ret = try_to_grab_pending(work, is_dwork, &flags);
/*
workqueue: fix hang involving racing cancel[_delayed]_work_sync()'s for PREEMPT_NONE cancel[_delayed]_work_sync() are implemented using __cancel_work_timer() which grabs the PENDING bit using try_to_grab_pending() and then flushes the work item with PENDING set to prevent the on-going execution of the work item from requeueing itself. try_to_grab_pending() can always grab PENDING bit without blocking except when someone else is doing the above flushing during cancelation. In that case, try_to_grab_pending() returns -ENOENT. In this case, __cancel_work_timer() currently invokes flush_work(). The assumption is that the completion of the work item is what the other canceling task would be waiting for too and thus waiting for the same condition and retrying should allow forward progress without excessive busy looping Unfortunately, this doesn't work if preemption is disabled or the latter task has real time priority. Let's say task A just got woken up from flush_work() by the completion of the target work item. If, before task A starts executing, task B gets scheduled and invokes __cancel_work_timer() on the same work item, its try_to_grab_pending() will return -ENOENT as the work item is still being canceled by task A and flush_work() will also immediately return false as the work item is no longer executing. This puts task B in a busy loop possibly preventing task A from executing and clearing the canceling state on the work item leading to a hang. task A task B worker executing work __cancel_work_timer() try_to_grab_pending() set work CANCELING flush_work() block for work completion completion, wakes up A __cancel_work_timer() while (forever) { try_to_grab_pending() -ENOENT as work is being canceled flush_work() false as work is no longer executing } This patch removes the possible hang by updating __cancel_work_timer() to explicitly wait for clearing of CANCELING rather than invoking flush_work() after try_to_grab_pending() fails with -ENOENT. Link: http://lkml.kernel.org/g/20150206171156.GA8942@axis.com v3: bit_waitqueue() can't be used for work items defined in vmalloc area. Switched to custom wake function which matches the target work item and exclusive wait and wakeup. v2: v1 used wake_up() on bit_waitqueue() which leads to NULL deref if the target bit waitqueue has wait_bit_queue's on it. Use DEFINE_WAIT_BIT() and __wake_up_bit() instead. Reported by Tomeu Vizoso. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Rabin Vincent <rabin.vincent@axis.com> Cc: Tomeu Vizoso <tomeu.vizoso@gmail.com> Cc: stable@vger.kernel.org Tested-by: Jesper Nilsson <jesper.nilsson@axis.com> Tested-by: Rabin Vincent <rabin.vincent@axis.com>
2015-03-05 13:04:13 +00:00
* If someone else is already canceling, wait for it to
* finish. flush_work() doesn't work for PREEMPT_NONE
* because we may get scheduled between @work's completion
* and the other canceling task resuming and clearing
* CANCELING - flush_work() will return false immediately
* as @work is no longer busy, try_to_grab_pending() will
* return -ENOENT as @work is still being canceled and the
* other canceling task won't be able to clear CANCELING as
* we're hogging the CPU.
*
* Let's wait for completion using a waitqueue. As this
* may lead to the thundering herd problem, use a custom
* wake function which matches @work along with exclusive
* wait and wakeup.
workqueue: mark a work item being canceled as such There can be two reasons try_to_grab_pending() can fail with -EAGAIN. One is when someone else is queueing or deqeueing the work item. With the previous patches, it is guaranteed that PENDING and queued state will soon agree making it safe to busy-retry in this case. The other is if multiple __cancel_work_timer() invocations are racing one another. __cancel_work_timer() grabs PENDING and then waits for running instances of the target work item on all CPUs while holding PENDING and !queued. try_to_grab_pending() invoked from another task will keep returning -EAGAIN while the current owner is waiting. Not distinguishing the two cases is okay because __cancel_work_timer() is the only user of try_to_grab_pending() and it invokes wait_on_work() whenever grabbing fails. For the first case, busy looping should be fine but wait_on_work() doesn't cause any critical problem. For the latter case, the new contender usually waits for the same condition as the current owner, so no unnecessarily extended busy-looping happens. Combined, these make __cancel_work_timer() technically correct even without irq protection while grabbing PENDING or distinguishing the two different cases. While the current code is technically correct, not distinguishing the two cases makes it difficult to use try_to_grab_pending() for other purposes than canceling because it's impossible to tell whether it's safe to busy-retry grabbing. This patch adds a mechanism to mark a work item being canceled. try_to_grab_pending() now disables irq on success and returns -EAGAIN to indicate that grabbing failed but PENDING and queued states are gonna agree soon and it's safe to busy-loop. It returns -ENOENT if the work item is being canceled and it may stay PENDING && !queued for arbitrary amount of time. __cancel_work_timer() is modified to mark the work canceling with WORK_OFFQ_CANCELING after grabbing PENDING, thus making try_to_grab_pending() fail with -ENOENT instead of -EAGAIN. Also, it invokes wait_on_work() iff grabbing failed with -ENOENT. This isn't necessary for correctness but makes it consistent with other future users of try_to_grab_pending(). v2: try_to_grab_pending() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Updated so that try_to_grab_pending() disables irq on success rather than requiring preemption disabled by the caller. This makes busy-looping easier and will allow try_to_grap_pending() to be used from bh/irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:46 +00:00
*/
workqueue: fix hang involving racing cancel[_delayed]_work_sync()'s for PREEMPT_NONE cancel[_delayed]_work_sync() are implemented using __cancel_work_timer() which grabs the PENDING bit using try_to_grab_pending() and then flushes the work item with PENDING set to prevent the on-going execution of the work item from requeueing itself. try_to_grab_pending() can always grab PENDING bit without blocking except when someone else is doing the above flushing during cancelation. In that case, try_to_grab_pending() returns -ENOENT. In this case, __cancel_work_timer() currently invokes flush_work(). The assumption is that the completion of the work item is what the other canceling task would be waiting for too and thus waiting for the same condition and retrying should allow forward progress without excessive busy looping Unfortunately, this doesn't work if preemption is disabled or the latter task has real time priority. Let's say task A just got woken up from flush_work() by the completion of the target work item. If, before task A starts executing, task B gets scheduled and invokes __cancel_work_timer() on the same work item, its try_to_grab_pending() will return -ENOENT as the work item is still being canceled by task A and flush_work() will also immediately return false as the work item is no longer executing. This puts task B in a busy loop possibly preventing task A from executing and clearing the canceling state on the work item leading to a hang. task A task B worker executing work __cancel_work_timer() try_to_grab_pending() set work CANCELING flush_work() block for work completion completion, wakes up A __cancel_work_timer() while (forever) { try_to_grab_pending() -ENOENT as work is being canceled flush_work() false as work is no longer executing } This patch removes the possible hang by updating __cancel_work_timer() to explicitly wait for clearing of CANCELING rather than invoking flush_work() after try_to_grab_pending() fails with -ENOENT. Link: http://lkml.kernel.org/g/20150206171156.GA8942@axis.com v3: bit_waitqueue() can't be used for work items defined in vmalloc area. Switched to custom wake function which matches the target work item and exclusive wait and wakeup. v2: v1 used wake_up() on bit_waitqueue() which leads to NULL deref if the target bit waitqueue has wait_bit_queue's on it. Use DEFINE_WAIT_BIT() and __wake_up_bit() instead. Reported by Tomeu Vizoso. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Rabin Vincent <rabin.vincent@axis.com> Cc: Tomeu Vizoso <tomeu.vizoso@gmail.com> Cc: stable@vger.kernel.org Tested-by: Jesper Nilsson <jesper.nilsson@axis.com> Tested-by: Rabin Vincent <rabin.vincent@axis.com>
2015-03-05 13:04:13 +00:00
if (unlikely(ret == -ENOENT)) {
struct cwt_wait cwait;
init_wait(&cwait.wait);
cwait.wait.func = cwt_wakefn;
cwait.work = work;
prepare_to_wait_exclusive(&cancel_waitq, &cwait.wait,
TASK_UNINTERRUPTIBLE);
if (work_is_canceling(work))
schedule();
finish_wait(&cancel_waitq, &cwait.wait);
}
} while (unlikely(ret < 0));
workqueue: mark a work item being canceled as such There can be two reasons try_to_grab_pending() can fail with -EAGAIN. One is when someone else is queueing or deqeueing the work item. With the previous patches, it is guaranteed that PENDING and queued state will soon agree making it safe to busy-retry in this case. The other is if multiple __cancel_work_timer() invocations are racing one another. __cancel_work_timer() grabs PENDING and then waits for running instances of the target work item on all CPUs while holding PENDING and !queued. try_to_grab_pending() invoked from another task will keep returning -EAGAIN while the current owner is waiting. Not distinguishing the two cases is okay because __cancel_work_timer() is the only user of try_to_grab_pending() and it invokes wait_on_work() whenever grabbing fails. For the first case, busy looping should be fine but wait_on_work() doesn't cause any critical problem. For the latter case, the new contender usually waits for the same condition as the current owner, so no unnecessarily extended busy-looping happens. Combined, these make __cancel_work_timer() technically correct even without irq protection while grabbing PENDING or distinguishing the two different cases. While the current code is technically correct, not distinguishing the two cases makes it difficult to use try_to_grab_pending() for other purposes than canceling because it's impossible to tell whether it's safe to busy-retry grabbing. This patch adds a mechanism to mark a work item being canceled. try_to_grab_pending() now disables irq on success and returns -EAGAIN to indicate that grabbing failed but PENDING and queued states are gonna agree soon and it's safe to busy-loop. It returns -ENOENT if the work item is being canceled and it may stay PENDING && !queued for arbitrary amount of time. __cancel_work_timer() is modified to mark the work canceling with WORK_OFFQ_CANCELING after grabbing PENDING, thus making try_to_grab_pending() fail with -ENOENT instead of -EAGAIN. Also, it invokes wait_on_work() iff grabbing failed with -ENOENT. This isn't necessary for correctness but makes it consistent with other future users of try_to_grab_pending(). v2: try_to_grab_pending() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Updated so that try_to_grab_pending() disables irq on success rather than requiring preemption disabled by the caller. This makes busy-looping easier and will allow try_to_grap_pending() to be used from bh/irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:46 +00:00
/* tell other tasks trying to grab @work to back off */
mark_work_canceling(work);
local_irq_restore(flags);
workqueue: make workqueue available early during boot Workqueue is currently initialized in an early init call; however, there are cases where early boot code has to be split and reordered to come after workqueue initialization or the same code path which makes use of workqueues is used both before workqueue initailization and after. The latter cases have to gate workqueue usages with keventd_up() tests, which is nasty and easy to get wrong. Workqueue usages have become widespread and it'd be a lot more convenient if it can be used very early from boot. This patch splits workqueue initialization into two steps. workqueue_init_early() which sets up the basic data structures so that workqueues can be created and work items queued, and workqueue_init() which actually brings up workqueues online and starts executing queued work items. The former step can be done very early during boot once memory allocation, cpumasks and idr are initialized. The latter right after kthreads become available. This allows work item queueing and canceling from very early boot which is what most of these use cases want. * As systemd_wq being initialized doesn't indicate that workqueue is fully online anymore, update keventd_up() to test wq_online instead. The follow-up patches will get rid of all its usages and the function itself. * Flushing doesn't make sense before workqueue is fully initialized. The flush functions trigger WARN and return immediately before fully online. * Work items are never in-flight before fully online. Canceling can always succeed by skipping the flush step. * Some code paths can no longer assume to be called with irq enabled as irq is disabled during early boot. Use irqsave/restore operations instead. v2: Watchdog init, which requires timer to be running, moved from workqueue_init_early() to workqueue_init(). Signed-off-by: Tejun Heo <tj@kernel.org> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/CA+55aFx0vPuMuxn00rBSM192n-Du5uxy+4AvKa0SBSOVJeuCGg@mail.gmail.com
2016-09-16 19:49:32 +00:00
/*
* This allows canceling during early boot. We know that @work
* isn't executing.
*/
if (wq_online)
flush_work(work);
clear_work_data(work);
workqueue: fix hang involving racing cancel[_delayed]_work_sync()'s for PREEMPT_NONE cancel[_delayed]_work_sync() are implemented using __cancel_work_timer() which grabs the PENDING bit using try_to_grab_pending() and then flushes the work item with PENDING set to prevent the on-going execution of the work item from requeueing itself. try_to_grab_pending() can always grab PENDING bit without blocking except when someone else is doing the above flushing during cancelation. In that case, try_to_grab_pending() returns -ENOENT. In this case, __cancel_work_timer() currently invokes flush_work(). The assumption is that the completion of the work item is what the other canceling task would be waiting for too and thus waiting for the same condition and retrying should allow forward progress without excessive busy looping Unfortunately, this doesn't work if preemption is disabled or the latter task has real time priority. Let's say task A just got woken up from flush_work() by the completion of the target work item. If, before task A starts executing, task B gets scheduled and invokes __cancel_work_timer() on the same work item, its try_to_grab_pending() will return -ENOENT as the work item is still being canceled by task A and flush_work() will also immediately return false as the work item is no longer executing. This puts task B in a busy loop possibly preventing task A from executing and clearing the canceling state on the work item leading to a hang. task A task B worker executing work __cancel_work_timer() try_to_grab_pending() set work CANCELING flush_work() block for work completion completion, wakes up A __cancel_work_timer() while (forever) { try_to_grab_pending() -ENOENT as work is being canceled flush_work() false as work is no longer executing } This patch removes the possible hang by updating __cancel_work_timer() to explicitly wait for clearing of CANCELING rather than invoking flush_work() after try_to_grab_pending() fails with -ENOENT. Link: http://lkml.kernel.org/g/20150206171156.GA8942@axis.com v3: bit_waitqueue() can't be used for work items defined in vmalloc area. Switched to custom wake function which matches the target work item and exclusive wait and wakeup. v2: v1 used wake_up() on bit_waitqueue() which leads to NULL deref if the target bit waitqueue has wait_bit_queue's on it. Use DEFINE_WAIT_BIT() and __wake_up_bit() instead. Reported by Tomeu Vizoso. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Rabin Vincent <rabin.vincent@axis.com> Cc: Tomeu Vizoso <tomeu.vizoso@gmail.com> Cc: stable@vger.kernel.org Tested-by: Jesper Nilsson <jesper.nilsson@axis.com> Tested-by: Rabin Vincent <rabin.vincent@axis.com>
2015-03-05 13:04:13 +00:00
/*
* Paired with prepare_to_wait() above so that either
* waitqueue_active() is visible here or !work_is_canceling() is
* visible there.
*/
smp_mb();
if (waitqueue_active(&cancel_waitq))
__wake_up(&cancel_waitq, TASK_NORMAL, 1, work);
return ret;
}
make cancel_rearming_delayed_work() reliable Thanks to Jarek Poplawski for the ideas and for spotting the bug in the initial draft patch. cancel_rearming_delayed_work() currently has many limitations, because it requires that dwork always re-arms itself via queue_delayed_work(). So it hangs forever if dwork doesn't do this, or cancel_rearming_delayed_work/ cancel_delayed_work was already called. It uses flush_workqueue() in a loop, so it can't be used if workqueue was freezed, and it is potentially live- lockable on busy system if delay is small. With this patch cancel_rearming_delayed_work() doesn't make any assumptions about dwork, it can re-arm itself via queue_delayed_work(), or queue_work(), or do nothing. As a "side effect", cancel_work_sync() was changed to handle re-arming works as well. Disadvantages: - this patch adds wmb() to insert_work(). - slowdowns the fast path (when del_timer() succeeds on entry) of cancel_rearming_delayed_work(), because wait_on_work() is called unconditionally. In that case, compared to the old version, we are doing "unneeded" lock/unlock for each online CPU. On the other hand, this means we don't need to use cancel_work_sync() after cancel_rearming_delayed_work(). - complicates the code (.text grows by 130 bytes). [akpm@linux-foundation.org: fix speling] Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: David Chinner <dgc@sgi.com> Cc: David Howells <dhowells@redhat.com> Cc: Gautham Shenoy <ego@in.ibm.com> Acked-by: Jarek Poplawski <jarkao2@o2.pl> Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-09 09:34:46 +00:00
/**
* cancel_work_sync - cancel a work and wait for it to finish
* @work: the work to cancel
make cancel_rearming_delayed_work() reliable Thanks to Jarek Poplawski for the ideas and for spotting the bug in the initial draft patch. cancel_rearming_delayed_work() currently has many limitations, because it requires that dwork always re-arms itself via queue_delayed_work(). So it hangs forever if dwork doesn't do this, or cancel_rearming_delayed_work/ cancel_delayed_work was already called. It uses flush_workqueue() in a loop, so it can't be used if workqueue was freezed, and it is potentially live- lockable on busy system if delay is small. With this patch cancel_rearming_delayed_work() doesn't make any assumptions about dwork, it can re-arm itself via queue_delayed_work(), or queue_work(), or do nothing. As a "side effect", cancel_work_sync() was changed to handle re-arming works as well. Disadvantages: - this patch adds wmb() to insert_work(). - slowdowns the fast path (when del_timer() succeeds on entry) of cancel_rearming_delayed_work(), because wait_on_work() is called unconditionally. In that case, compared to the old version, we are doing "unneeded" lock/unlock for each online CPU. On the other hand, this means we don't need to use cancel_work_sync() after cancel_rearming_delayed_work(). - complicates the code (.text grows by 130 bytes). [akpm@linux-foundation.org: fix speling] Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: David Chinner <dgc@sgi.com> Cc: David Howells <dhowells@redhat.com> Cc: Gautham Shenoy <ego@in.ibm.com> Acked-by: Jarek Poplawski <jarkao2@o2.pl> Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-09 09:34:46 +00:00
*
* Cancel @work and wait for its execution to finish. This function
* can be used even if the work re-queues itself or migrates to
* another workqueue. On return from this function, @work is
* guaranteed to be not pending or executing on any CPU.
*
* cancel_work_sync(&delayed_work->work) must not be used for
* delayed_work's. Use cancel_delayed_work_sync() instead.
make cancel_rearming_delayed_work() reliable Thanks to Jarek Poplawski for the ideas and for spotting the bug in the initial draft patch. cancel_rearming_delayed_work() currently has many limitations, because it requires that dwork always re-arms itself via queue_delayed_work(). So it hangs forever if dwork doesn't do this, or cancel_rearming_delayed_work/ cancel_delayed_work was already called. It uses flush_workqueue() in a loop, so it can't be used if workqueue was freezed, and it is potentially live- lockable on busy system if delay is small. With this patch cancel_rearming_delayed_work() doesn't make any assumptions about dwork, it can re-arm itself via queue_delayed_work(), or queue_work(), or do nothing. As a "side effect", cancel_work_sync() was changed to handle re-arming works as well. Disadvantages: - this patch adds wmb() to insert_work(). - slowdowns the fast path (when del_timer() succeeds on entry) of cancel_rearming_delayed_work(), because wait_on_work() is called unconditionally. In that case, compared to the old version, we are doing "unneeded" lock/unlock for each online CPU. On the other hand, this means we don't need to use cancel_work_sync() after cancel_rearming_delayed_work(). - complicates the code (.text grows by 130 bytes). [akpm@linux-foundation.org: fix speling] Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: David Chinner <dgc@sgi.com> Cc: David Howells <dhowells@redhat.com> Cc: Gautham Shenoy <ego@in.ibm.com> Acked-by: Jarek Poplawski <jarkao2@o2.pl> Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-09 09:34:46 +00:00
*
* The caller must ensure that the workqueue on which @work was last
make cancel_rearming_delayed_work() reliable Thanks to Jarek Poplawski for the ideas and for spotting the bug in the initial draft patch. cancel_rearming_delayed_work() currently has many limitations, because it requires that dwork always re-arms itself via queue_delayed_work(). So it hangs forever if dwork doesn't do this, or cancel_rearming_delayed_work/ cancel_delayed_work was already called. It uses flush_workqueue() in a loop, so it can't be used if workqueue was freezed, and it is potentially live- lockable on busy system if delay is small. With this patch cancel_rearming_delayed_work() doesn't make any assumptions about dwork, it can re-arm itself via queue_delayed_work(), or queue_work(), or do nothing. As a "side effect", cancel_work_sync() was changed to handle re-arming works as well. Disadvantages: - this patch adds wmb() to insert_work(). - slowdowns the fast path (when del_timer() succeeds on entry) of cancel_rearming_delayed_work(), because wait_on_work() is called unconditionally. In that case, compared to the old version, we are doing "unneeded" lock/unlock for each online CPU. On the other hand, this means we don't need to use cancel_work_sync() after cancel_rearming_delayed_work(). - complicates the code (.text grows by 130 bytes). [akpm@linux-foundation.org: fix speling] Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: David Chinner <dgc@sgi.com> Cc: David Howells <dhowells@redhat.com> Cc: Gautham Shenoy <ego@in.ibm.com> Acked-by: Jarek Poplawski <jarkao2@o2.pl> Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-09 09:34:46 +00:00
* queued can't be destroyed before this function returns.
*
* Return:
* %true if @work was pending, %false otherwise.
make cancel_rearming_delayed_work() reliable Thanks to Jarek Poplawski for the ideas and for spotting the bug in the initial draft patch. cancel_rearming_delayed_work() currently has many limitations, because it requires that dwork always re-arms itself via queue_delayed_work(). So it hangs forever if dwork doesn't do this, or cancel_rearming_delayed_work/ cancel_delayed_work was already called. It uses flush_workqueue() in a loop, so it can't be used if workqueue was freezed, and it is potentially live- lockable on busy system if delay is small. With this patch cancel_rearming_delayed_work() doesn't make any assumptions about dwork, it can re-arm itself via queue_delayed_work(), or queue_work(), or do nothing. As a "side effect", cancel_work_sync() was changed to handle re-arming works as well. Disadvantages: - this patch adds wmb() to insert_work(). - slowdowns the fast path (when del_timer() succeeds on entry) of cancel_rearming_delayed_work(), because wait_on_work() is called unconditionally. In that case, compared to the old version, we are doing "unneeded" lock/unlock for each online CPU. On the other hand, this means we don't need to use cancel_work_sync() after cancel_rearming_delayed_work(). - complicates the code (.text grows by 130 bytes). [akpm@linux-foundation.org: fix speling] Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: David Chinner <dgc@sgi.com> Cc: David Howells <dhowells@redhat.com> Cc: Gautham Shenoy <ego@in.ibm.com> Acked-by: Jarek Poplawski <jarkao2@o2.pl> Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-09 09:34:46 +00:00
*/
bool cancel_work_sync(struct work_struct *work)
make cancel_rearming_delayed_work() reliable Thanks to Jarek Poplawski for the ideas and for spotting the bug in the initial draft patch. cancel_rearming_delayed_work() currently has many limitations, because it requires that dwork always re-arms itself via queue_delayed_work(). So it hangs forever if dwork doesn't do this, or cancel_rearming_delayed_work/ cancel_delayed_work was already called. It uses flush_workqueue() in a loop, so it can't be used if workqueue was freezed, and it is potentially live- lockable on busy system if delay is small. With this patch cancel_rearming_delayed_work() doesn't make any assumptions about dwork, it can re-arm itself via queue_delayed_work(), or queue_work(), or do nothing. As a "side effect", cancel_work_sync() was changed to handle re-arming works as well. Disadvantages: - this patch adds wmb() to insert_work(). - slowdowns the fast path (when del_timer() succeeds on entry) of cancel_rearming_delayed_work(), because wait_on_work() is called unconditionally. In that case, compared to the old version, we are doing "unneeded" lock/unlock for each online CPU. On the other hand, this means we don't need to use cancel_work_sync() after cancel_rearming_delayed_work(). - complicates the code (.text grows by 130 bytes). [akpm@linux-foundation.org: fix speling] Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: David Chinner <dgc@sgi.com> Cc: David Howells <dhowells@redhat.com> Cc: Gautham Shenoy <ego@in.ibm.com> Acked-by: Jarek Poplawski <jarkao2@o2.pl> Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-09 09:34:46 +00:00
{
return __cancel_work_timer(work, false);
implement flush_work() A basic problem with flush_scheduled_work() is that it blocks behind _all_ presently-queued works, rather than just the work whcih the caller wants to flush. If the caller holds some lock, and if one of the queued work happens to want that lock as well then accidental deadlocks can occur. One example of this is the phy layer: it wants to flush work while holding rtnl_lock(). But if a linkwatch event happens to be queued, the phy code will deadlock because the linkwatch callback function takes rtnl_lock. So we implement a new function which will flush a *single* work - just the one which the caller wants to free up. Thus we avoid the accidental deadlocks which can arise from unrelated subsystems' callbacks taking shared locks. flush_work() non-blockingly dequeues the work_struct which we want to kill, then it waits for its handler to complete on all CPUs. Add ->current_work to the "struct cpu_workqueue_struct", it points to currently running "struct work_struct". When flush_work(work) detects ->current_work == work, it inserts a barrier at the _head_ of ->worklist (and thus right _after_ that work) and waits for completition. This means that the next work fired on that CPU will be this barrier, or another barrier queued by concurrent flush_work(), so the caller of flush_work() will be woken before any "regular" work has a chance to run. When wait_on_work() unlocks workqueue_mutex (or whatever we choose to protect against CPU hotplug), CPU may go away. But in that case take_over_work() will move a barrier we queued to another CPU, it will be fired sometime, and wait_on_work() will be woken. Actually, we are doing cleanup_workqueue_thread()->kthread_stop() before take_over_work(), so cwq->thread should complete its ->worklist (and thus the barrier), because currently we don't check kthread_should_stop() in run_workqueue(). But even if we did, everything should be ok. [akpm@osdl.org: cleanup] [akpm@osdl.org: add flush_work_keventd() wrapper] Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-09 09:33:52 +00:00
}
EXPORT_SYMBOL_GPL(cancel_work_sync);
implement flush_work() A basic problem with flush_scheduled_work() is that it blocks behind _all_ presently-queued works, rather than just the work whcih the caller wants to flush. If the caller holds some lock, and if one of the queued work happens to want that lock as well then accidental deadlocks can occur. One example of this is the phy layer: it wants to flush work while holding rtnl_lock(). But if a linkwatch event happens to be queued, the phy code will deadlock because the linkwatch callback function takes rtnl_lock. So we implement a new function which will flush a *single* work - just the one which the caller wants to free up. Thus we avoid the accidental deadlocks which can arise from unrelated subsystems' callbacks taking shared locks. flush_work() non-blockingly dequeues the work_struct which we want to kill, then it waits for its handler to complete on all CPUs. Add ->current_work to the "struct cpu_workqueue_struct", it points to currently running "struct work_struct". When flush_work(work) detects ->current_work == work, it inserts a barrier at the _head_ of ->worklist (and thus right _after_ that work) and waits for completition. This means that the next work fired on that CPU will be this barrier, or another barrier queued by concurrent flush_work(), so the caller of flush_work() will be woken before any "regular" work has a chance to run. When wait_on_work() unlocks workqueue_mutex (or whatever we choose to protect against CPU hotplug), CPU may go away. But in that case take_over_work() will move a barrier we queued to another CPU, it will be fired sometime, and wait_on_work() will be woken. Actually, we are doing cleanup_workqueue_thread()->kthread_stop() before take_over_work(), so cwq->thread should complete its ->worklist (and thus the barrier), because currently we don't check kthread_should_stop() in run_workqueue(). But even if we did, everything should be ok. [akpm@osdl.org: cleanup] [akpm@osdl.org: add flush_work_keventd() wrapper] Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-09 09:33:52 +00:00
make cancel_rearming_delayed_work() reliable Thanks to Jarek Poplawski for the ideas and for spotting the bug in the initial draft patch. cancel_rearming_delayed_work() currently has many limitations, because it requires that dwork always re-arms itself via queue_delayed_work(). So it hangs forever if dwork doesn't do this, or cancel_rearming_delayed_work/ cancel_delayed_work was already called. It uses flush_workqueue() in a loop, so it can't be used if workqueue was freezed, and it is potentially live- lockable on busy system if delay is small. With this patch cancel_rearming_delayed_work() doesn't make any assumptions about dwork, it can re-arm itself via queue_delayed_work(), or queue_work(), or do nothing. As a "side effect", cancel_work_sync() was changed to handle re-arming works as well. Disadvantages: - this patch adds wmb() to insert_work(). - slowdowns the fast path (when del_timer() succeeds on entry) of cancel_rearming_delayed_work(), because wait_on_work() is called unconditionally. In that case, compared to the old version, we are doing "unneeded" lock/unlock for each online CPU. On the other hand, this means we don't need to use cancel_work_sync() after cancel_rearming_delayed_work(). - complicates the code (.text grows by 130 bytes). [akpm@linux-foundation.org: fix speling] Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: David Chinner <dgc@sgi.com> Cc: David Howells <dhowells@redhat.com> Cc: Gautham Shenoy <ego@in.ibm.com> Acked-by: Jarek Poplawski <jarkao2@o2.pl> Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-09 09:34:46 +00:00
/**
* flush_delayed_work - wait for a dwork to finish executing the last queueing
* @dwork: the delayed work to flush
make cancel_rearming_delayed_work() reliable Thanks to Jarek Poplawski for the ideas and for spotting the bug in the initial draft patch. cancel_rearming_delayed_work() currently has many limitations, because it requires that dwork always re-arms itself via queue_delayed_work(). So it hangs forever if dwork doesn't do this, or cancel_rearming_delayed_work/ cancel_delayed_work was already called. It uses flush_workqueue() in a loop, so it can't be used if workqueue was freezed, and it is potentially live- lockable on busy system if delay is small. With this patch cancel_rearming_delayed_work() doesn't make any assumptions about dwork, it can re-arm itself via queue_delayed_work(), or queue_work(), or do nothing. As a "side effect", cancel_work_sync() was changed to handle re-arming works as well. Disadvantages: - this patch adds wmb() to insert_work(). - slowdowns the fast path (when del_timer() succeeds on entry) of cancel_rearming_delayed_work(), because wait_on_work() is called unconditionally. In that case, compared to the old version, we are doing "unneeded" lock/unlock for each online CPU. On the other hand, this means we don't need to use cancel_work_sync() after cancel_rearming_delayed_work(). - complicates the code (.text grows by 130 bytes). [akpm@linux-foundation.org: fix speling] Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: David Chinner <dgc@sgi.com> Cc: David Howells <dhowells@redhat.com> Cc: Gautham Shenoy <ego@in.ibm.com> Acked-by: Jarek Poplawski <jarkao2@o2.pl> Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-09 09:34:46 +00:00
*
* Delayed timer is cancelled and the pending work is queued for
* immediate execution. Like flush_work(), this function only
* considers the last queueing instance of @dwork.
*
* Return:
* %true if flush_work() waited for the work to finish execution,
* %false if it was already idle.
make cancel_rearming_delayed_work() reliable Thanks to Jarek Poplawski for the ideas and for spotting the bug in the initial draft patch. cancel_rearming_delayed_work() currently has many limitations, because it requires that dwork always re-arms itself via queue_delayed_work(). So it hangs forever if dwork doesn't do this, or cancel_rearming_delayed_work/ cancel_delayed_work was already called. It uses flush_workqueue() in a loop, so it can't be used if workqueue was freezed, and it is potentially live- lockable on busy system if delay is small. With this patch cancel_rearming_delayed_work() doesn't make any assumptions about dwork, it can re-arm itself via queue_delayed_work(), or queue_work(), or do nothing. As a "side effect", cancel_work_sync() was changed to handle re-arming works as well. Disadvantages: - this patch adds wmb() to insert_work(). - slowdowns the fast path (when del_timer() succeeds on entry) of cancel_rearming_delayed_work(), because wait_on_work() is called unconditionally. In that case, compared to the old version, we are doing "unneeded" lock/unlock for each online CPU. On the other hand, this means we don't need to use cancel_work_sync() after cancel_rearming_delayed_work(). - complicates the code (.text grows by 130 bytes). [akpm@linux-foundation.org: fix speling] Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: David Chinner <dgc@sgi.com> Cc: David Howells <dhowells@redhat.com> Cc: Gautham Shenoy <ego@in.ibm.com> Acked-by: Jarek Poplawski <jarkao2@o2.pl> Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-09 09:34:46 +00:00
*/
bool flush_delayed_work(struct delayed_work *dwork)
{
workqueue: disable irq while manipulating PENDING Queueing operations use WORK_STRUCT_PENDING_BIT to synchronize access to the target work item. They first try to claim the bit and proceed with queueing only after that succeeds and there's a window between PENDING being set and the actual queueing where the task can be interrupted or preempted. There's also a similar window in process_one_work() when clearing PENDING. A work item is dequeued, gcwq->lock is released and then PENDING is cleared and the worker might get interrupted or preempted between releasing gcwq->lock and clearing PENDING. cancel[_delayed]_work_sync() tries to claim or steal PENDING. The function assumes that a work item with PENDING is either queued or in the process of being [de]queued. In the latter case, it busy-loops until either the work item loses PENDING or is queued. If canceling coincides with the above described interrupts or preemptions, the canceling task will busy-loop while the queueing or executing task is preempted. This patch keeps irq disabled across claiming PENDING and actual queueing and moves PENDING clearing in process_one_work() inside gcwq->lock so that busy looping from PENDING && !queued doesn't wait for interrupted/preempted tasks. Note that, in process_one_work(), setting last CPU and clearing PENDING got merged into single operation. This removes possible long busy-loops and will allow using try_to_grab_pending() from bh and irq contexts. v2: __queue_work() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Disable irq instead of preemption. IRQ will be disabled while grabbing gcwq->lock later anyway and this allows using try_to_grab_pending() from bh and irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:45 +00:00
local_irq_disable();
if (del_timer_sync(&dwork->timer))
workqueue: add delayed_work->wq to simplify reentrancy handling To avoid executing the same work item from multiple CPUs concurrently, a work_struct records the last pool it was on in its ->data so that, on the next queueing, the pool can be queried to determine whether the work item is still executing or not. A delayed_work goes through timer before actually being queued on the target workqueue and the timer needs to know the target workqueue and CPU. This is currently achieved by modifying delayed_work->work.data such that it points to the cwq which points to the target workqueue and the last CPU the work item was on. __queue_delayed_work() extracts the last CPU from delayed_work->work.data and then combines it with the target workqueue to create new work.data. The only thing this rather ugly hack achieves is encoding the target workqueue into delayed_work->work.data without using a separate field, which could be a trade off one can make; unfortunately, this entangles work->data management between regular workqueue and delayed_work code by setting cwq pointer before the work item is actually queued and becomes a hindrance for further improvements of work->data handling. This can be easily made sane by adding a target workqueue field to delayed_work. While delayed_work is used widely in the kernel and this does make it a bit larger (<5%), I think this is the right trade-off especially given the prospect of much saner handling of work->data which currently involves quite tricky memory barrier dancing, and don't expect to see any measureable effect. Add delayed_work->wq and drop the delayed_work->work.data overloading. tj: Rewrote the description. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2013-02-07 02:04:53 +00:00
__queue_work(dwork->cpu, dwork->wq, &dwork->work);
workqueue: disable irq while manipulating PENDING Queueing operations use WORK_STRUCT_PENDING_BIT to synchronize access to the target work item. They first try to claim the bit and proceed with queueing only after that succeeds and there's a window between PENDING being set and the actual queueing where the task can be interrupted or preempted. There's also a similar window in process_one_work() when clearing PENDING. A work item is dequeued, gcwq->lock is released and then PENDING is cleared and the worker might get interrupted or preempted between releasing gcwq->lock and clearing PENDING. cancel[_delayed]_work_sync() tries to claim or steal PENDING. The function assumes that a work item with PENDING is either queued or in the process of being [de]queued. In the latter case, it busy-loops until either the work item loses PENDING or is queued. If canceling coincides with the above described interrupts or preemptions, the canceling task will busy-loop while the queueing or executing task is preempted. This patch keeps irq disabled across claiming PENDING and actual queueing and moves PENDING clearing in process_one_work() inside gcwq->lock so that busy looping from PENDING && !queued doesn't wait for interrupted/preempted tasks. Note that, in process_one_work(), setting last CPU and clearing PENDING got merged into single operation. This removes possible long busy-loops and will allow using try_to_grab_pending() from bh and irq contexts. v2: __queue_work() was testing preempt_count() to ensure that the caller has disabled preemption. This triggers spuriously if !CONFIG_PREEMPT_COUNT. Use preemptible() instead. Reported by Fengguang Wu. v3: Disable irq instead of preemption. IRQ will be disabled while grabbing gcwq->lock later anyway and this allows using try_to_grab_pending() from bh and irq contexts. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com>
2012-08-03 17:30:45 +00:00
local_irq_enable();
return flush_work(&dwork->work);
}
EXPORT_SYMBOL(flush_delayed_work);
/**
* cancel_delayed_work - cancel a delayed work
* @dwork: delayed_work to cancel
*
* Kill off a pending delayed_work.
*
* Return: %true if @dwork was pending and canceled; %false if it wasn't
* pending.
*
* Note:
* The work callback function may still be running on return, unless
* it returns %true and the work doesn't re-arm itself. Explicitly flush or
* use cancel_delayed_work_sync() to wait on it.
*
* This function is safe to call from any context including IRQ handler.
*/
bool cancel_delayed_work(struct delayed_work *dwork)
{
unsigned long flags;
int ret;
do {
ret = try_to_grab_pending(&dwork->work, true, &flags);
} while (unlikely(ret == -EAGAIN));
if (unlikely(ret < 0))
return false;
set_work_pool_and_clear_pending(&dwork->work,
get_work_pool_id(&dwork->work));
local_irq_restore(flags);
return ret;
}
EXPORT_SYMBOL(cancel_delayed_work);
/**
* cancel_delayed_work_sync - cancel a delayed work and wait for it to finish
* @dwork: the delayed work cancel
*
* This is cancel_work_sync() for delayed works.
*
* Return:
* %true if @dwork was pending, %false otherwise.
*/
bool cancel_delayed_work_sync(struct delayed_work *dwork)
make cancel_rearming_delayed_work() reliable Thanks to Jarek Poplawski for the ideas and for spotting the bug in the initial draft patch. cancel_rearming_delayed_work() currently has many limitations, because it requires that dwork always re-arms itself via queue_delayed_work(). So it hangs forever if dwork doesn't do this, or cancel_rearming_delayed_work/ cancel_delayed_work was already called. It uses flush_workqueue() in a loop, so it can't be used if workqueue was freezed, and it is potentially live- lockable on busy system if delay is small. With this patch cancel_rearming_delayed_work() doesn't make any assumptions about dwork, it can re-arm itself via queue_delayed_work(), or queue_work(), or do nothing. As a "side effect", cancel_work_sync() was changed to handle re-arming works as well. Disadvantages: - this patch adds wmb() to insert_work(). - slowdowns the fast path (when del_timer() succeeds on entry) of cancel_rearming_delayed_work(), because wait_on_work() is called unconditionally. In that case, compared to the old version, we are doing "unneeded" lock/unlock for each online CPU. On the other hand, this means we don't need to use cancel_work_sync() after cancel_rearming_delayed_work(). - complicates the code (.text grows by 130 bytes). [akpm@linux-foundation.org: fix speling] Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: David Chinner <dgc@sgi.com> Cc: David Howells <dhowells@redhat.com> Cc: Gautham Shenoy <ego@in.ibm.com> Acked-by: Jarek Poplawski <jarkao2@o2.pl> Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-09 09:34:46 +00:00
{
return __cancel_work_timer(&dwork->work, true);
make cancel_rearming_delayed_work() reliable Thanks to Jarek Poplawski for the ideas and for spotting the bug in the initial draft patch. cancel_rearming_delayed_work() currently has many limitations, because it requires that dwork always re-arms itself via queue_delayed_work(). So it hangs forever if dwork doesn't do this, or cancel_rearming_delayed_work/ cancel_delayed_work was already called. It uses flush_workqueue() in a loop, so it can't be used if workqueue was freezed, and it is potentially live- lockable on busy system if delay is small. With this patch cancel_rearming_delayed_work() doesn't make any assumptions about dwork, it can re-arm itself via queue_delayed_work(), or queue_work(), or do nothing. As a "side effect", cancel_work_sync() was changed to handle re-arming works as well. Disadvantages: - this patch adds wmb() to insert_work(). - slowdowns the fast path (when del_timer() succeeds on entry) of cancel_rearming_delayed_work(), because wait_on_work() is called unconditionally. In that case, compared to the old version, we are doing "unneeded" lock/unlock for each online CPU. On the other hand, this means we don't need to use cancel_work_sync() after cancel_rearming_delayed_work(). - complicates the code (.text grows by 130 bytes). [akpm@linux-foundation.org: fix speling] Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: David Chinner <dgc@sgi.com> Cc: David Howells <dhowells@redhat.com> Cc: Gautham Shenoy <ego@in.ibm.com> Acked-by: Jarek Poplawski <jarkao2@o2.pl> Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-09 09:34:46 +00:00
}
EXPORT_SYMBOL(cancel_delayed_work_sync);
/**
* schedule_on_each_cpu - execute a function synchronously on each online CPU
* @func: the function to call
*
* schedule_on_each_cpu() executes @func on each online CPU using the
* system workqueue and blocks until all CPUs have completed.
* schedule_on_each_cpu() is very slow.
*
* Return:
* 0 on success, -errno on failure.
*/
2006-11-22 14:55:48 +00:00
int schedule_on_each_cpu(work_func_t func)
{
int cpu;
struct work_struct __percpu *works;
works = alloc_percpu(struct work_struct);
if (!works)
return -ENOMEM;
get_online_cpus();
for_each_online_cpu(cpu) {
struct work_struct *work = per_cpu_ptr(works, cpu);
INIT_WORK(work, func);
schedule_work_on(cpu, work);
}
for_each_online_cpu(cpu)
flush_work(per_cpu_ptr(works, cpu));
put_online_cpus();
free_percpu(works);
return 0;
}
/**
* execute_in_process_context - reliably execute the routine with user context
* @fn: the function to execute
* @ew: guaranteed storage for the execute work structure (must
* be available when the work executes)
*
* Executes the function immediately if process context is available,
* otherwise schedules the function for delayed execution.
*
* Return: 0 - function was executed
* 1 - function was scheduled for execution
*/
2006-11-22 14:55:48 +00:00
int execute_in_process_context(work_func_t fn, struct execute_work *ew)
{
if (!in_interrupt()) {
2006-11-22 14:55:48 +00:00
fn(&ew->work);
return 0;
}
2006-11-22 14:55:48 +00:00
INIT_WORK(&ew->work, fn);
schedule_work(&ew->work);
return 1;
}
EXPORT_SYMBOL_GPL(execute_in_process_context);
/**
* free_workqueue_attrs - free a workqueue_attrs
* @attrs: workqueue_attrs to free
*
* Undo alloc_workqueue_attrs().
*/
void free_workqueue_attrs(struct workqueue_attrs *attrs)
{
if (attrs) {
free_cpumask_var(attrs->cpumask);
kfree(attrs);
}
}
/**
* alloc_workqueue_attrs - allocate a workqueue_attrs
* @gfp_mask: allocation mask to use
*
* Allocate a new workqueue_attrs, initialize with default settings and
* return it.
*
* Return: The allocated new workqueue_attr on success. %NULL on failure.
*/
struct workqueue_attrs *alloc_workqueue_attrs(gfp_t gfp_mask)
{
struct workqueue_attrs *attrs;
attrs = kzalloc(sizeof(*attrs), gfp_mask);
if (!attrs)
goto fail;
if (!alloc_cpumask_var(&attrs->cpumask, gfp_mask))
goto fail;
cpumask_copy(attrs->cpumask, cpu_possible_mask);
return attrs;
fail:
free_workqueue_attrs(attrs);
return NULL;
}
static void copy_workqueue_attrs(struct workqueue_attrs *to,
const struct workqueue_attrs *from)
{
to->nice = from->nice;
cpumask_copy(to->cpumask, from->cpumask);
/*
* Unlike hash and equality test, this function doesn't ignore
* ->no_numa as it is used for both pool and wq attrs. Instead,
* get_unbound_pool() explicitly clears ->no_numa after copying.
*/
to->no_numa = from->no_numa;
}
/* hash value of the content of @attr */
static u32 wqattrs_hash(const struct workqueue_attrs *attrs)
{
u32 hash = 0;
hash = jhash_1word(attrs->nice, hash);
hash = jhash(cpumask_bits(attrs->cpumask),
BITS_TO_LONGS(nr_cpumask_bits) * sizeof(long), hash);
return hash;
}
/* content equality test */
static bool wqattrs_equal(const struct workqueue_attrs *a,
const struct workqueue_attrs *b)
{
if (a->nice != b->nice)
return false;
if (!cpumask_equal(a->cpumask, b->cpumask))
return false;
return true;
}
/**
* init_worker_pool - initialize a newly zalloc'd worker_pool
* @pool: worker_pool to initialize
*
* Initialize a newly zalloc'd @pool. It also allocates @pool->attrs.
*
* Return: 0 on success, -errno on failure. Even on failure, all fields
* inside @pool proper are initialized and put_unbound_pool() can be called
* on @pool safely to release it.
*/
static int init_worker_pool(struct worker_pool *pool)
{
spin_lock_init(&pool->lock);
pool->id = -1;
pool->cpu = -1;
pool->node = NUMA_NO_NODE;
pool->flags |= POOL_DISASSOCIATED;
workqueue: implement lockup detector Workqueue stalls can happen from a variety of usage bugs such as missing WQ_MEM_RECLAIM flag or concurrency managed work item indefinitely staying RUNNING. These stalls can be extremely difficult to hunt down because the usual warning mechanisms can't detect workqueue stalls and the internal state is pretty opaque. To alleviate the situation, this patch implements workqueue lockup detector. It periodically monitors all worker_pools periodically and, if any pool failed to make forward progress longer than the threshold duration, triggers warning and dumps workqueue state as follows. BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 31s! Showing busy workqueues and worker pools: workqueue events: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=17/256 pending: monkey_wrench_fn, e1000_watchdog, cache_reap, vmstat_shepherd, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, cgroup_release_agent workqueue events_power_efficient: flags=0x80 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=2/256 pending: check_lifetime, neigh_periodic_work workqueue cgroup_pidlist_destroy: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/1 pending: cgroup_pidlist_destroy_work_fn ... The detection mechanism is controller through kernel parameter workqueue.watchdog_thresh and can be updated at runtime through the sysfs module parameter file. v2: Decoupled from softlockup control knobs. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Don Zickus <dzickus@redhat.com> Cc: Ulrich Obergfell <uobergfe@redhat.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Chris Mason <clm@fb.com> Cc: Andrew Morton <akpm@linux-foundation.org>
2015-12-08 16:28:04 +00:00
pool->watchdog_ts = jiffies;
INIT_LIST_HEAD(&pool->worklist);
INIT_LIST_HEAD(&pool->idle_list);
hash_init(pool->busy_hash);
init_timer_deferrable(&pool->idle_timer);
pool->idle_timer.function = idle_worker_timeout;
pool->idle_timer.data = (unsigned long)pool;
setup_timer(&pool->mayday_timer, pool_mayday_timeout,
(unsigned long)pool);
mutex_init(&pool->manager_arb);
mutex_init(&pool->attach_mutex);
INIT_LIST_HEAD(&pool->workers);
ida_init(&pool->worker_ida);
INIT_HLIST_NODE(&pool->hash_node);
pool->refcnt = 1;
/* shouldn't fail above this point */
pool->attrs = alloc_workqueue_attrs(GFP_KERNEL);
if (!pool->attrs)
return -ENOMEM;
return 0;
}
static void rcu_free_wq(struct rcu_head *rcu)
{
struct workqueue_struct *wq =
container_of(rcu, struct workqueue_struct, rcu);
if (!(wq->flags & WQ_UNBOUND))
free_percpu(wq->cpu_pwqs);
else
free_workqueue_attrs(wq->unbound_attrs);
kfree(wq->rescuer);
kfree(wq);
}
static void rcu_free_pool(struct rcu_head *rcu)
{
struct worker_pool *pool = container_of(rcu, struct worker_pool, rcu);
ida_destroy(&pool->worker_ida);
free_workqueue_attrs(pool->attrs);
kfree(pool);
}
/**
* put_unbound_pool - put a worker_pool
* @pool: worker_pool to put
*
* Put @pool. If its refcnt reaches zero, it gets destroyed in sched-RCU
* safe manner. get_unbound_pool() calls this function on its failure path
* and this function should be able to release pools which went through,
* successfully or not, init_worker_pool().
*
* Should be called with wq_pool_mutex held.
*/
static void put_unbound_pool(struct worker_pool *pool)
{
DECLARE_COMPLETION_ONSTACK(detach_completion);
struct worker *worker;
lockdep_assert_held(&wq_pool_mutex);
if (--pool->refcnt)
return;
/* sanity checks */
if (WARN_ON(!(pool->cpu < 0)) ||
WARN_ON(!list_empty(&pool->worklist)))
return;
/* release id and unhash */
if (pool->id >= 0)
idr_remove(&worker_pool_idr, pool->id);
hash_del(&pool->hash_node);
/*
* Become the manager and destroy all workers. Grabbing
* manager_arb prevents @pool's workers from blocking on
* attach_mutex.
*/
mutex_lock(&pool->manager_arb);
spin_lock_irq(&pool->lock);
while ((worker = first_idle_worker(pool)))
destroy_worker(worker);
WARN_ON(pool->nr_workers || pool->nr_idle);
spin_unlock_irq(&pool->lock);
mutex_lock(&pool->attach_mutex);
if (!list_empty(&pool->workers))
pool->detach_completion = &detach_completion;
mutex_unlock(&pool->attach_mutex);
if (pool->detach_completion)
wait_for_completion(pool->detach_completion);
mutex_unlock(&pool->manager_arb);
/* shut down the timers */
del_timer_sync(&pool->idle_timer);
del_timer_sync(&pool->mayday_timer);
/* sched-RCU protected to allow dereferences from get_work_pool() */
call_rcu_sched(&pool->rcu, rcu_free_pool);
}
/**
* get_unbound_pool - get a worker_pool with the specified attributes
* @attrs: the attributes of the worker_pool to get
*
* Obtain a worker_pool which has the same attributes as @attrs, bump the
* reference count and return it. If there already is a matching
* worker_pool, it will be used; otherwise, this function attempts to
* create a new one.
*
* Should be called with wq_pool_mutex held.
*
* Return: On success, a worker_pool with the same attributes as @attrs.
* On failure, %NULL.
*/
static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
{
u32 hash = wqattrs_hash(attrs);
struct worker_pool *pool;
int node;
int target_node = NUMA_NO_NODE;
lockdep_assert_held(&wq_pool_mutex);
/* do we already have a matching pool? */
hash_for_each_possible(unbound_pool_hash, pool, hash_node, hash) {
if (wqattrs_equal(pool->attrs, attrs)) {
pool->refcnt++;
return pool;
}
}
/* if cpumask is contained inside a NUMA node, we belong to that node */
if (wq_numa_enabled) {
for_each_node(node) {
if (cpumask_subset(attrs->cpumask,
wq_numa_possible_cpumask[node])) {
target_node = node;
break;
}
}
}
/* nope, create a new one */
pool = kzalloc_node(sizeof(*pool), GFP_KERNEL, target_node);
if (!pool || init_worker_pool(pool) < 0)
goto fail;
lockdep_set_subclass(&pool->lock, 1); /* see put_pwq() */
copy_workqueue_attrs(pool->attrs, attrs);
pool->node = target_node;
/*
* no_numa isn't a worker_pool attribute, always clear it. See
* 'struct workqueue_attrs' comments for detail.
*/
pool->attrs->no_numa = false;
if (worker_pool_assign_id(pool) < 0)
goto fail;
/* create and start the initial worker */
workqueue: make workqueue available early during boot Workqueue is currently initialized in an early init call; however, there are cases where early boot code has to be split and reordered to come after workqueue initialization or the same code path which makes use of workqueues is used both before workqueue initailization and after. The latter cases have to gate workqueue usages with keventd_up() tests, which is nasty and easy to get wrong. Workqueue usages have become widespread and it'd be a lot more convenient if it can be used very early from boot. This patch splits workqueue initialization into two steps. workqueue_init_early() which sets up the basic data structures so that workqueues can be created and work items queued, and workqueue_init() which actually brings up workqueues online and starts executing queued work items. The former step can be done very early during boot once memory allocation, cpumasks and idr are initialized. The latter right after kthreads become available. This allows work item queueing and canceling from very early boot which is what most of these use cases want. * As systemd_wq being initialized doesn't indicate that workqueue is fully online anymore, update keventd_up() to test wq_online instead. The follow-up patches will get rid of all its usages and the function itself. * Flushing doesn't make sense before workqueue is fully initialized. The flush functions trigger WARN and return immediately before fully online. * Work items are never in-flight before fully online. Canceling can always succeed by skipping the flush step. * Some code paths can no longer assume to be called with irq enabled as irq is disabled during early boot. Use irqsave/restore operations instead. v2: Watchdog init, which requires timer to be running, moved from workqueue_init_early() to workqueue_init(). Signed-off-by: Tejun Heo <tj@kernel.org> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/CA+55aFx0vPuMuxn00rBSM192n-Du5uxy+4AvKa0SBSOVJeuCGg@mail.gmail.com
2016-09-16 19:49:32 +00:00
if (wq_online && !create_worker(pool))
goto fail;
/* install */
hash_add(unbound_pool_hash, &pool->hash_node, hash);
return pool;
fail:
if (pool)
put_unbound_pool(pool);
return NULL;
}
static void rcu_free_pwq(struct rcu_head *rcu)
{
kmem_cache_free(pwq_cache,
container_of(rcu, struct pool_workqueue, rcu));
}
/*
* Scheduled on system_wq by put_pwq() when an unbound pwq hits zero refcnt
* and needs to be destroyed.
*/
static void pwq_unbound_release_workfn(struct work_struct *work)
{
struct pool_workqueue *pwq = container_of(work, struct pool_workqueue,
unbound_release_work);
struct workqueue_struct *wq = pwq->wq;
struct worker_pool *pool = pwq->pool;
bool is_last;
if (WARN_ON_ONCE(!(wq->flags & WQ_UNBOUND)))
return;
mutex_lock(&wq->mutex);
list_del_rcu(&pwq->pwqs_node);
is_last = list_empty(&wq->pwqs);
mutex_unlock(&wq->mutex);
mutex_lock(&wq_pool_mutex);
put_unbound_pool(pool);
mutex_unlock(&wq_pool_mutex);
call_rcu_sched(&pwq->rcu, rcu_free_pwq);
/*
* If we're the last pwq going away, @wq is already dead and no one
* is gonna access it anymore. Schedule RCU free.
*/
if (is_last)
call_rcu_sched(&wq->rcu, rcu_free_wq);
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
}
/**
* pwq_adjust_max_active - update a pwq's max_active to the current setting
* @pwq: target pool_workqueue
*
* If @pwq isn't freezing, set @pwq->max_active to the associated
* workqueue's saved_max_active and activate delayed work items
* accordingly. If @pwq is freezing, clear @pwq->max_active to zero.
*/
static void pwq_adjust_max_active(struct pool_workqueue *pwq)
{
struct workqueue_struct *wq = pwq->wq;
bool freezable = wq->flags & WQ_FREEZABLE;
workqueue: make workqueue available early during boot Workqueue is currently initialized in an early init call; however, there are cases where early boot code has to be split and reordered to come after workqueue initialization or the same code path which makes use of workqueues is used both before workqueue initailization and after. The latter cases have to gate workqueue usages with keventd_up() tests, which is nasty and easy to get wrong. Workqueue usages have become widespread and it'd be a lot more convenient if it can be used very early from boot. This patch splits workqueue initialization into two steps. workqueue_init_early() which sets up the basic data structures so that workqueues can be created and work items queued, and workqueue_init() which actually brings up workqueues online and starts executing queued work items. The former step can be done very early during boot once memory allocation, cpumasks and idr are initialized. The latter right after kthreads become available. This allows work item queueing and canceling from very early boot which is what most of these use cases want. * As systemd_wq being initialized doesn't indicate that workqueue is fully online anymore, update keventd_up() to test wq_online instead. The follow-up patches will get rid of all its usages and the function itself. * Flushing doesn't make sense before workqueue is fully initialized. The flush functions trigger WARN and return immediately before fully online. * Work items are never in-flight before fully online. Canceling can always succeed by skipping the flush step. * Some code paths can no longer assume to be called with irq enabled as irq is disabled during early boot. Use irqsave/restore operations instead. v2: Watchdog init, which requires timer to be running, moved from workqueue_init_early() to workqueue_init(). Signed-off-by: Tejun Heo <tj@kernel.org> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/CA+55aFx0vPuMuxn00rBSM192n-Du5uxy+4AvKa0SBSOVJeuCGg@mail.gmail.com
2016-09-16 19:49:32 +00:00
unsigned long flags;
/* for @wq->saved_max_active */
lockdep_assert_held(&wq->mutex);
/* fast exit for non-freezable wqs */
if (!freezable && pwq->max_active == wq->saved_max_active)
return;
workqueue: make workqueue available early during boot Workqueue is currently initialized in an early init call; however, there are cases where early boot code has to be split and reordered to come after workqueue initialization or the same code path which makes use of workqueues is used both before workqueue initailization and after. The latter cases have to gate workqueue usages with keventd_up() tests, which is nasty and easy to get wrong. Workqueue usages have become widespread and it'd be a lot more convenient if it can be used very early from boot. This patch splits workqueue initialization into two steps. workqueue_init_early() which sets up the basic data structures so that workqueues can be created and work items queued, and workqueue_init() which actually brings up workqueues online and starts executing queued work items. The former step can be done very early during boot once memory allocation, cpumasks and idr are initialized. The latter right after kthreads become available. This allows work item queueing and canceling from very early boot which is what most of these use cases want. * As systemd_wq being initialized doesn't indicate that workqueue is fully online anymore, update keventd_up() to test wq_online instead. The follow-up patches will get rid of all its usages and the function itself. * Flushing doesn't make sense before workqueue is fully initialized. The flush functions trigger WARN and return immediately before fully online. * Work items are never in-flight before fully online. Canceling can always succeed by skipping the flush step. * Some code paths can no longer assume to be called with irq enabled as irq is disabled during early boot. Use irqsave/restore operations instead. v2: Watchdog init, which requires timer to be running, moved from workqueue_init_early() to workqueue_init(). Signed-off-by: Tejun Heo <tj@kernel.org> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/CA+55aFx0vPuMuxn00rBSM192n-Du5uxy+4AvKa0SBSOVJeuCGg@mail.gmail.com
2016-09-16 19:49:32 +00:00
/* this function can be called during early boot w/ irq disabled */
spin_lock_irqsave(&pwq->pool->lock, flags);
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
/*
* During [un]freezing, the caller is responsible for ensuring that
* this function is called at least once after @workqueue_freezing
* is updated and visible.
*/
if (!freezable || !workqueue_freezing) {
pwq->max_active = wq->saved_max_active;
while (!list_empty(&pwq->delayed_works) &&
pwq->nr_active < pwq->max_active)
pwq_activate_first_delayed(pwq);
/*
* Need to kick a worker after thawed or an unbound wq's
* max_active is bumped. It's a slow path. Do it always.
*/
wake_up_worker(pwq->pool);
} else {
pwq->max_active = 0;
}
workqueue: make workqueue available early during boot Workqueue is currently initialized in an early init call; however, there are cases where early boot code has to be split and reordered to come after workqueue initialization or the same code path which makes use of workqueues is used both before workqueue initailization and after. The latter cases have to gate workqueue usages with keventd_up() tests, which is nasty and easy to get wrong. Workqueue usages have become widespread and it'd be a lot more convenient if it can be used very early from boot. This patch splits workqueue initialization into two steps. workqueue_init_early() which sets up the basic data structures so that workqueues can be created and work items queued, and workqueue_init() which actually brings up workqueues online and starts executing queued work items. The former step can be done very early during boot once memory allocation, cpumasks and idr are initialized. The latter right after kthreads become available. This allows work item queueing and canceling from very early boot which is what most of these use cases want. * As systemd_wq being initialized doesn't indicate that workqueue is fully online anymore, update keventd_up() to test wq_online instead. The follow-up patches will get rid of all its usages and the function itself. * Flushing doesn't make sense before workqueue is fully initialized. The flush functions trigger WARN and return immediately before fully online. * Work items are never in-flight before fully online. Canceling can always succeed by skipping the flush step. * Some code paths can no longer assume to be called with irq enabled as irq is disabled during early boot. Use irqsave/restore operations instead. v2: Watchdog init, which requires timer to be running, moved from workqueue_init_early() to workqueue_init(). Signed-off-by: Tejun Heo <tj@kernel.org> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/CA+55aFx0vPuMuxn00rBSM192n-Du5uxy+4AvKa0SBSOVJeuCGg@mail.gmail.com
2016-09-16 19:49:32 +00:00
spin_unlock_irqrestore(&pwq->pool->lock, flags);
}
/* initialize newly alloced @pwq which is associated with @wq and @pool */
static void init_pwq(struct pool_workqueue *pwq, struct workqueue_struct *wq,
struct worker_pool *pool)
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
{
BUG_ON((unsigned long)pwq & WORK_STRUCT_FLAG_MASK);
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
memset(pwq, 0, sizeof(*pwq));
pwq->pool = pool;
pwq->wq = wq;
pwq->flush_color = -1;
pwq->refcnt = 1;
INIT_LIST_HEAD(&pwq->delayed_works);
INIT_LIST_HEAD(&pwq->pwqs_node);
INIT_LIST_HEAD(&pwq->mayday_node);
INIT_WORK(&pwq->unbound_release_work, pwq_unbound_release_workfn);
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
}
/* sync @pwq with the current state of its associated wq and link it */
static void link_pwq(struct pool_workqueue *pwq)
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
{
struct workqueue_struct *wq = pwq->wq;
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
lockdep_assert_held(&wq->mutex);
/* may be called multiple times, ignore if already linked */
if (!list_empty(&pwq->pwqs_node))
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
return;
/* set the matching work_color */
pwq->work_color = wq->work_color;
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
/* sync max_active to the current setting */
pwq_adjust_max_active(pwq);
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
/* link in @pwq */
list_add_rcu(&pwq->pwqs_node, &wq->pwqs);
}
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
/* obtain a pool matching @attr and create a pwq associating the pool and @wq */
static struct pool_workqueue *alloc_unbound_pwq(struct workqueue_struct *wq,
const struct workqueue_attrs *attrs)
{
struct worker_pool *pool;
struct pool_workqueue *pwq;
workqueue: async worker destruction worker destruction includes these parts of code: adjust pool's stats remove the worker from idle list detach the worker from the pool kthread_stop() to wait for the worker's task exit free the worker struct We can find out that there is no essential work to do after kthread_stop(), which means destroy_worker() doesn't need to wait for the worker's task exit, so we can remove kthread_stop() and free the worker struct in the worker exiting path. However, put_unbound_pool() still needs to sync the all the workers' destruction before destroying the pool; otherwise, the workers may access to the invalid pool when they are exiting. So we also move the code of "detach the worker" to the exiting path and let put_unbound_pool() to sync with this code via detach_completion. The code of "detach the worker" is wrapped in a new function "worker_detach_from_pool()" although worker_detach_from_pool() is only called once (in worker_thread()) after this patch, but we need to wrap it for these reasons: 1) The code of "detach the worker" is not short enough to unfold them in worker_thread(). 2) the name of "worker_detach_from_pool()" is self-comment, and we add some comments above the function. 3) it will be shared by rescuer in later patch which allows rescuer and normal thread use the same attach/detach frameworks. The worker id is freed when detaching which happens before the worker is fully dead, but this id of the dying worker may be re-used for a new worker, so the dying worker's task name is changed to "worker/dying" to avoid two or several workers having the same name. Since "detach the worker" is moved out from destroy_worker(), destroy_worker() doesn't require manager_mutex, so the "lockdep_assert_held(&pool->manager_mutex)" in destroy_worker() is removed, and destroy_worker() is not protected by manager_mutex in put_unbound_pool(). tj: Minor description updates. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2014-05-20 09:46:29 +00:00
lockdep_assert_held(&wq_pool_mutex);
workqueue: async worker destruction worker destruction includes these parts of code: adjust pool's stats remove the worker from idle list detach the worker from the pool kthread_stop() to wait for the worker's task exit free the worker struct We can find out that there is no essential work to do after kthread_stop(), which means destroy_worker() doesn't need to wait for the worker's task exit, so we can remove kthread_stop() and free the worker struct in the worker exiting path. However, put_unbound_pool() still needs to sync the all the workers' destruction before destroying the pool; otherwise, the workers may access to the invalid pool when they are exiting. So we also move the code of "detach the worker" to the exiting path and let put_unbound_pool() to sync with this code via detach_completion. The code of "detach the worker" is wrapped in a new function "worker_detach_from_pool()" although worker_detach_from_pool() is only called once (in worker_thread()) after this patch, but we need to wrap it for these reasons: 1) The code of "detach the worker" is not short enough to unfold them in worker_thread(). 2) the name of "worker_detach_from_pool()" is self-comment, and we add some comments above the function. 3) it will be shared by rescuer in later patch which allows rescuer and normal thread use the same attach/detach frameworks. The worker id is freed when detaching which happens before the worker is fully dead, but this id of the dying worker may be re-used for a new worker, so the dying worker's task name is changed to "worker/dying" to avoid two or several workers having the same name. Since "detach the worker" is moved out from destroy_worker(), destroy_worker() doesn't require manager_mutex, so the "lockdep_assert_held(&pool->manager_mutex)" in destroy_worker() is removed, and destroy_worker() is not protected by manager_mutex in put_unbound_pool(). tj: Minor description updates. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2014-05-20 09:46:29 +00:00
pool = get_unbound_pool(attrs);
if (!pool)
return NULL;
workqueue: async worker destruction worker destruction includes these parts of code: adjust pool's stats remove the worker from idle list detach the worker from the pool kthread_stop() to wait for the worker's task exit free the worker struct We can find out that there is no essential work to do after kthread_stop(), which means destroy_worker() doesn't need to wait for the worker's task exit, so we can remove kthread_stop() and free the worker struct in the worker exiting path. However, put_unbound_pool() still needs to sync the all the workers' destruction before destroying the pool; otherwise, the workers may access to the invalid pool when they are exiting. So we also move the code of "detach the worker" to the exiting path and let put_unbound_pool() to sync with this code via detach_completion. The code of "detach the worker" is wrapped in a new function "worker_detach_from_pool()" although worker_detach_from_pool() is only called once (in worker_thread()) after this patch, but we need to wrap it for these reasons: 1) The code of "detach the worker" is not short enough to unfold them in worker_thread(). 2) the name of "worker_detach_from_pool()" is self-comment, and we add some comments above the function. 3) it will be shared by rescuer in later patch which allows rescuer and normal thread use the same attach/detach frameworks. The worker id is freed when detaching which happens before the worker is fully dead, but this id of the dying worker may be re-used for a new worker, so the dying worker's task name is changed to "worker/dying" to avoid two or several workers having the same name. Since "detach the worker" is moved out from destroy_worker(), destroy_worker() doesn't require manager_mutex, so the "lockdep_assert_held(&pool->manager_mutex)" in destroy_worker() is removed, and destroy_worker() is not protected by manager_mutex in put_unbound_pool(). tj: Minor description updates. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2014-05-20 09:46:29 +00:00
pwq = kmem_cache_alloc_node(pwq_cache, GFP_KERNEL, pool->node);
if (!pwq) {
put_unbound_pool(pool);
return NULL;
}
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
init_pwq(pwq, wq, pool);
return pwq;
}
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
/**
* wq_calc_node_cpumask - calculate a wq_attrs' cpumask for the specified node
workqueue: Allow modifying low level unbound workqueue cpumask Allow to modify the low-level unbound workqueues cpumask through sysfs. This is performed by traversing the entire workqueue list and calling apply_wqattrs_prepare() on the unbound workqueues with the new low level mask. Only after all the preparation are done, we commit them all together. Ordered workqueues are ignored from the low level unbound workqueue cpumask, it will be handled in near future. All the (default & per-node) pwqs are mandatorily controlled by the low level cpumask. If the user configured cpumask doesn't overlap with the low level cpumask, the low level cpumask will be used for the wq instead. The comment of wq_calc_node_cpumask() is updated and explicitly requires that its first argument should be the attrs of the default pwq. The default wq_unbound_cpumask is cpu_possible_mask. The workqueue subsystem doesn't know its best default value, let the system manager or the other subsystem set it when needed. Changed from V8: merge the calculating code for the attrs of the default pwq together. minor change the code&comments for saving the user configured attrs. remove unnecessary list_del(). minor update the comment of wq_calc_node_cpumask(). update the comment of workqueue_set_unbound_cpumask(); Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Original-patch-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-30 09:16:12 +00:00
* @attrs: the wq_attrs of the default pwq of the target workqueue
* @node: the target NUMA node
* @cpu_going_down: if >= 0, the CPU to consider as offline
* @cpumask: outarg, the resulting cpumask
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
*
* Calculate the cpumask a workqueue with @attrs should use on @node. If
* @cpu_going_down is >= 0, that cpu is considered offline during
* calculation. The result is stored in @cpumask.
*
* If NUMA affinity is not enabled, @attrs->cpumask is always used. If
* enabled and @node has online CPUs requested by @attrs, the returned
* cpumask is the intersection of the possible CPUs of @node and
* @attrs->cpumask.
*
* The caller is responsible for ensuring that the cpumask of @node stays
* stable.
*
* Return: %true if the resulting @cpumask is different from @attrs->cpumask,
* %false if equal.
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
*/
static bool wq_calc_node_cpumask(const struct workqueue_attrs *attrs, int node,
int cpu_going_down, cpumask_t *cpumask)
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
{
if (!wq_numa_enabled || attrs->no_numa)
goto use_dfl;
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
/* does @node have any online CPUs @attrs wants? */
cpumask_and(cpumask, cpumask_of_node(node), attrs->cpumask);
if (cpu_going_down >= 0)
cpumask_clear_cpu(cpu_going_down, cpumask);
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
if (cpumask_empty(cpumask))
goto use_dfl;
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
/* yeap, return possible CPUs in @node that @attrs wants */
cpumask_and(cpumask, attrs->cpumask, wq_numa_possible_cpumask[node]);
return !cpumask_equal(cpumask, attrs->cpumask);
use_dfl:
cpumask_copy(cpumask, attrs->cpumask);
return false;
}
/* install @pwq into @wq's numa_pwq_tbl[] for @node and return the old pwq */
static struct pool_workqueue *numa_pwq_tbl_install(struct workqueue_struct *wq,
int node,
struct pool_workqueue *pwq)
{
struct pool_workqueue *old_pwq;
lockdep_assert_held(&wq_pool_mutex);
lockdep_assert_held(&wq->mutex);
/* link_pwq() can handle duplicate calls */
link_pwq(pwq);
old_pwq = rcu_access_pointer(wq->numa_pwq_tbl[node]);
rcu_assign_pointer(wq->numa_pwq_tbl[node], pwq);
return old_pwq;
}
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
/* context to store the prepared attrs & pwqs before applying */
struct apply_wqattrs_ctx {
struct workqueue_struct *wq; /* target workqueue */
struct workqueue_attrs *attrs; /* attrs to apply */
workqueue: Allow modifying low level unbound workqueue cpumask Allow to modify the low-level unbound workqueues cpumask through sysfs. This is performed by traversing the entire workqueue list and calling apply_wqattrs_prepare() on the unbound workqueues with the new low level mask. Only after all the preparation are done, we commit them all together. Ordered workqueues are ignored from the low level unbound workqueue cpumask, it will be handled in near future. All the (default & per-node) pwqs are mandatorily controlled by the low level cpumask. If the user configured cpumask doesn't overlap with the low level cpumask, the low level cpumask will be used for the wq instead. The comment of wq_calc_node_cpumask() is updated and explicitly requires that its first argument should be the attrs of the default pwq. The default wq_unbound_cpumask is cpu_possible_mask. The workqueue subsystem doesn't know its best default value, let the system manager or the other subsystem set it when needed. Changed from V8: merge the calculating code for the attrs of the default pwq together. minor change the code&comments for saving the user configured attrs. remove unnecessary list_del(). minor update the comment of wq_calc_node_cpumask(). update the comment of workqueue_set_unbound_cpumask(); Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Original-patch-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-30 09:16:12 +00:00
struct list_head list; /* queued for batching commit */
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
struct pool_workqueue *dfl_pwq;
struct pool_workqueue *pwq_tbl[];
};
/* free the resources after success or abort */
static void apply_wqattrs_cleanup(struct apply_wqattrs_ctx *ctx)
{
if (ctx) {
int node;
for_each_node(node)
put_pwq_unlocked(ctx->pwq_tbl[node]);
put_pwq_unlocked(ctx->dfl_pwq);
free_workqueue_attrs(ctx->attrs);
kfree(ctx);
}
}
/* allocate the attrs and pwqs for later installation */
static struct apply_wqattrs_ctx *
apply_wqattrs_prepare(struct workqueue_struct *wq,
const struct workqueue_attrs *attrs)
{
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
struct apply_wqattrs_ctx *ctx;
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
struct workqueue_attrs *new_attrs, *tmp_attrs;
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
int node;
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
lockdep_assert_held(&wq_pool_mutex);
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
ctx = kzalloc(sizeof(*ctx) + nr_node_ids * sizeof(ctx->pwq_tbl[0]),
GFP_KERNEL);
new_attrs = alloc_workqueue_attrs(GFP_KERNEL);
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
tmp_attrs = alloc_workqueue_attrs(GFP_KERNEL);
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
if (!ctx || !new_attrs || !tmp_attrs)
goto out_free;
workqueue: Allow modifying low level unbound workqueue cpumask Allow to modify the low-level unbound workqueues cpumask through sysfs. This is performed by traversing the entire workqueue list and calling apply_wqattrs_prepare() on the unbound workqueues with the new low level mask. Only after all the preparation are done, we commit them all together. Ordered workqueues are ignored from the low level unbound workqueue cpumask, it will be handled in near future. All the (default & per-node) pwqs are mandatorily controlled by the low level cpumask. If the user configured cpumask doesn't overlap with the low level cpumask, the low level cpumask will be used for the wq instead. The comment of wq_calc_node_cpumask() is updated and explicitly requires that its first argument should be the attrs of the default pwq. The default wq_unbound_cpumask is cpu_possible_mask. The workqueue subsystem doesn't know its best default value, let the system manager or the other subsystem set it when needed. Changed from V8: merge the calculating code for the attrs of the default pwq together. minor change the code&comments for saving the user configured attrs. remove unnecessary list_del(). minor update the comment of wq_calc_node_cpumask(). update the comment of workqueue_set_unbound_cpumask(); Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Original-patch-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-30 09:16:12 +00:00
/*
* Calculate the attrs of the default pwq.
* If the user configured cpumask doesn't overlap with the
* wq_unbound_cpumask, we fallback to the wq_unbound_cpumask.
*/
copy_workqueue_attrs(new_attrs, attrs);
cpumask_and(new_attrs->cpumask, new_attrs->cpumask, wq_unbound_cpumask);
workqueue: Allow modifying low level unbound workqueue cpumask Allow to modify the low-level unbound workqueues cpumask through sysfs. This is performed by traversing the entire workqueue list and calling apply_wqattrs_prepare() on the unbound workqueues with the new low level mask. Only after all the preparation are done, we commit them all together. Ordered workqueues are ignored from the low level unbound workqueue cpumask, it will be handled in near future. All the (default & per-node) pwqs are mandatorily controlled by the low level cpumask. If the user configured cpumask doesn't overlap with the low level cpumask, the low level cpumask will be used for the wq instead. The comment of wq_calc_node_cpumask() is updated and explicitly requires that its first argument should be the attrs of the default pwq. The default wq_unbound_cpumask is cpu_possible_mask. The workqueue subsystem doesn't know its best default value, let the system manager or the other subsystem set it when needed. Changed from V8: merge the calculating code for the attrs of the default pwq together. minor change the code&comments for saving the user configured attrs. remove unnecessary list_del(). minor update the comment of wq_calc_node_cpumask(). update the comment of workqueue_set_unbound_cpumask(); Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Original-patch-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-30 09:16:12 +00:00
if (unlikely(cpumask_empty(new_attrs->cpumask)))
cpumask_copy(new_attrs->cpumask, wq_unbound_cpumask);
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
/*
* We may create multiple pwqs with differing cpumasks. Make a
* copy of @new_attrs which will be modified and used to obtain
* pools.
*/
copy_workqueue_attrs(tmp_attrs, new_attrs);
/*
* If something goes wrong during CPU up/down, we'll fall back to
* the default pwq covering whole @attrs->cpumask. Always create
* it even if we don't use it immediately.
*/
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
ctx->dfl_pwq = alloc_unbound_pwq(wq, new_attrs);
if (!ctx->dfl_pwq)
goto out_free;
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
for_each_node(node) {
workqueue: Allow modifying low level unbound workqueue cpumask Allow to modify the low-level unbound workqueues cpumask through sysfs. This is performed by traversing the entire workqueue list and calling apply_wqattrs_prepare() on the unbound workqueues with the new low level mask. Only after all the preparation are done, we commit them all together. Ordered workqueues are ignored from the low level unbound workqueue cpumask, it will be handled in near future. All the (default & per-node) pwqs are mandatorily controlled by the low level cpumask. If the user configured cpumask doesn't overlap with the low level cpumask, the low level cpumask will be used for the wq instead. The comment of wq_calc_node_cpumask() is updated and explicitly requires that its first argument should be the attrs of the default pwq. The default wq_unbound_cpumask is cpu_possible_mask. The workqueue subsystem doesn't know its best default value, let the system manager or the other subsystem set it when needed. Changed from V8: merge the calculating code for the attrs of the default pwq together. minor change the code&comments for saving the user configured attrs. remove unnecessary list_del(). minor update the comment of wq_calc_node_cpumask(). update the comment of workqueue_set_unbound_cpumask(); Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Original-patch-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-30 09:16:12 +00:00
if (wq_calc_node_cpumask(new_attrs, node, -1, tmp_attrs->cpumask)) {
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
ctx->pwq_tbl[node] = alloc_unbound_pwq(wq, tmp_attrs);
if (!ctx->pwq_tbl[node])
goto out_free;
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
} else {
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
ctx->dfl_pwq->refcnt++;
ctx->pwq_tbl[node] = ctx->dfl_pwq;
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
}
}
workqueue: Allow modifying low level unbound workqueue cpumask Allow to modify the low-level unbound workqueues cpumask through sysfs. This is performed by traversing the entire workqueue list and calling apply_wqattrs_prepare() on the unbound workqueues with the new low level mask. Only after all the preparation are done, we commit them all together. Ordered workqueues are ignored from the low level unbound workqueue cpumask, it will be handled in near future. All the (default & per-node) pwqs are mandatorily controlled by the low level cpumask. If the user configured cpumask doesn't overlap with the low level cpumask, the low level cpumask will be used for the wq instead. The comment of wq_calc_node_cpumask() is updated and explicitly requires that its first argument should be the attrs of the default pwq. The default wq_unbound_cpumask is cpu_possible_mask. The workqueue subsystem doesn't know its best default value, let the system manager or the other subsystem set it when needed. Changed from V8: merge the calculating code for the attrs of the default pwq together. minor change the code&comments for saving the user configured attrs. remove unnecessary list_del(). minor update the comment of wq_calc_node_cpumask(). update the comment of workqueue_set_unbound_cpumask(); Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Original-patch-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-30 09:16:12 +00:00
/* save the user configured attrs and sanitize it. */
copy_workqueue_attrs(new_attrs, attrs);
cpumask_and(new_attrs->cpumask, new_attrs->cpumask, cpu_possible_mask);
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
ctx->attrs = new_attrs;
workqueue: Allow modifying low level unbound workqueue cpumask Allow to modify the low-level unbound workqueues cpumask through sysfs. This is performed by traversing the entire workqueue list and calling apply_wqattrs_prepare() on the unbound workqueues with the new low level mask. Only after all the preparation are done, we commit them all together. Ordered workqueues are ignored from the low level unbound workqueue cpumask, it will be handled in near future. All the (default & per-node) pwqs are mandatorily controlled by the low level cpumask. If the user configured cpumask doesn't overlap with the low level cpumask, the low level cpumask will be used for the wq instead. The comment of wq_calc_node_cpumask() is updated and explicitly requires that its first argument should be the attrs of the default pwq. The default wq_unbound_cpumask is cpu_possible_mask. The workqueue subsystem doesn't know its best default value, let the system manager or the other subsystem set it when needed. Changed from V8: merge the calculating code for the attrs of the default pwq together. minor change the code&comments for saving the user configured attrs. remove unnecessary list_del(). minor update the comment of wq_calc_node_cpumask(). update the comment of workqueue_set_unbound_cpumask(); Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Original-patch-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-30 09:16:12 +00:00
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
ctx->wq = wq;
free_workqueue_attrs(tmp_attrs);
return ctx;
out_free:
free_workqueue_attrs(tmp_attrs);
free_workqueue_attrs(new_attrs);
apply_wqattrs_cleanup(ctx);
return NULL;
}
/* set attrs and install prepared pwqs, @ctx points to old pwqs on return */
static void apply_wqattrs_commit(struct apply_wqattrs_ctx *ctx)
{
int node;
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
/* all pwqs have been created successfully, let's install'em */
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
mutex_lock(&ctx->wq->mutex);
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
copy_workqueue_attrs(ctx->wq->unbound_attrs, ctx->attrs);
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
/* save the previous pwq and install the new one */
for_each_node(node)
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
ctx->pwq_tbl[node] = numa_pwq_tbl_install(ctx->wq, node,
ctx->pwq_tbl[node]);
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
/* @dfl_pwq might not have been used, ensure it's linked */
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
link_pwq(ctx->dfl_pwq);
swap(ctx->wq->dfl_pwq, ctx->dfl_pwq);
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
mutex_unlock(&ctx->wq->mutex);
}
static void apply_wqattrs_lock(void)
{
/* CPUs should stay stable across pwq creations and installations */
get_online_cpus();
mutex_lock(&wq_pool_mutex);
}
static void apply_wqattrs_unlock(void)
{
mutex_unlock(&wq_pool_mutex);
put_online_cpus();
}
static int apply_workqueue_attrs_locked(struct workqueue_struct *wq,
const struct workqueue_attrs *attrs)
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
{
struct apply_wqattrs_ctx *ctx;
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
/* only unbound workqueues can change attributes */
if (WARN_ON(!(wq->flags & WQ_UNBOUND)))
return -EINVAL;
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
/* creating multiple pwqs breaks ordering guarantee */
if (WARN_ON((wq->flags & __WQ_ORDERED) && !list_empty(&wq->pwqs)))
return -EINVAL;
ctx = apply_wqattrs_prepare(wq, attrs);
if (!ctx)
return -ENOMEM;
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
/* the ctx has been prepared successfully, let's commit it */
apply_wqattrs_commit(ctx);
workqueue: split apply_workqueue_attrs() into 3 stages Current apply_workqueue_attrs() includes pwqs-allocation and pwqs-installation, so when we batch multiple apply_workqueue_attrs()s as a transaction, we can't ensure the transaction must succeed or fail as a complete unit. To solve this, we split apply_workqueue_attrs() into three stages. The first stage does the preparation: allocation memory, pwqs. The second stage does the attrs-installaion and pwqs-installation. The third stage frees the allocated memory and (old or unused) pwqs. As the result, batching multiple apply_workqueue_attrs()s can succeed or fail as a complete unit: 1) batch do all the first stage for all the workqueues 2) only commit all when all the above succeed. This patch is a preparation for the next patch ("Allow modifying low level unbound workqueue cpumask") which will do a multiple apply_workqueue_attrs(). The patch doesn't have functionality changed except two minor adjustment: 1) free_unbound_pwq() for the error path is removed, we use the heavier version put_pwq_unlocked() instead since the error path is rare. this adjustment simplifies the code. 2) the memory-allocation is also moved into wq_pool_mutex. this is needed to avoid to do the further splitting. tj: minor updates to comments. Suggested-by: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-27 09:58:38 +00:00
apply_wqattrs_cleanup(ctx);
return 0;
}
/**
* apply_workqueue_attrs - apply new workqueue_attrs to an unbound workqueue
* @wq: the target workqueue
* @attrs: the workqueue_attrs to apply, allocated with alloc_workqueue_attrs()
*
* Apply @attrs to an unbound workqueue @wq. Unless disabled, on NUMA
* machines, this function maps a separate pwq to each NUMA node with
* possibles CPUs in @attrs->cpumask so that work items are affine to the
* NUMA node it was issued on. Older pwqs are released as in-flight work
* items finish. Note that a work item which repeatedly requeues itself
* back-to-back will stay on its current pwq.
*
* Performs GFP_KERNEL allocations.
*
* Return: 0 on success and -errno on failure.
*/
int apply_workqueue_attrs(struct workqueue_struct *wq,
const struct workqueue_attrs *attrs)
{
int ret;
apply_wqattrs_lock();
ret = apply_workqueue_attrs_locked(wq, attrs);
apply_wqattrs_unlock();
return ret;
}
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
/**
* wq_update_unbound_numa - update NUMA affinity of a wq for CPU hot[un]plug
* @wq: the target workqueue
* @cpu: the CPU coming up or going down
* @online: whether @cpu is coming up or going down
*
* This function is to be called from %CPU_DOWN_PREPARE, %CPU_ONLINE and
* %CPU_DOWN_FAILED. @cpu is being hot[un]plugged, update NUMA affinity of
* @wq accordingly.
*
* If NUMA affinity can't be adjusted due to memory allocation failure, it
* falls back to @wq->dfl_pwq which may not be optimal but is always
* correct.
*
* Note that when the last allowed CPU of a NUMA node goes offline for a
* workqueue with a cpumask spanning multiple nodes, the workers which were
* already executing the work items for the workqueue will lose their CPU
* affinity and may execute on any CPU. This is similar to how per-cpu
* workqueues behave on CPU_DOWN. If a workqueue user wants strict
* affinity, it's the user's responsibility to flush the work item from
* CPU_DOWN_PREPARE.
*/
static void wq_update_unbound_numa(struct workqueue_struct *wq, int cpu,
bool online)
{
int node = cpu_to_node(cpu);
int cpu_off = online ? -1 : cpu;
struct pool_workqueue *old_pwq = NULL, *pwq;
struct workqueue_attrs *target_attrs;
cpumask_t *cpumask;
lockdep_assert_held(&wq_pool_mutex);
if (!wq_numa_enabled || !(wq->flags & WQ_UNBOUND) ||
wq->unbound_attrs->no_numa)
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
return;
/*
* We don't wanna alloc/free wq_attrs for each wq for each CPU.
* Let's use a preallocated one. The following buf is protected by
* CPU hotplug exclusion.
*/
target_attrs = wq_update_unbound_numa_attrs_buf;
cpumask = target_attrs->cpumask;
copy_workqueue_attrs(target_attrs, wq->unbound_attrs);
pwq = unbound_pwq_by_node(wq, node);
/*
* Let's determine what needs to be done. If the target cpumask is
workqueue: Allow modifying low level unbound workqueue cpumask Allow to modify the low-level unbound workqueues cpumask through sysfs. This is performed by traversing the entire workqueue list and calling apply_wqattrs_prepare() on the unbound workqueues with the new low level mask. Only after all the preparation are done, we commit them all together. Ordered workqueues are ignored from the low level unbound workqueue cpumask, it will be handled in near future. All the (default & per-node) pwqs are mandatorily controlled by the low level cpumask. If the user configured cpumask doesn't overlap with the low level cpumask, the low level cpumask will be used for the wq instead. The comment of wq_calc_node_cpumask() is updated and explicitly requires that its first argument should be the attrs of the default pwq. The default wq_unbound_cpumask is cpu_possible_mask. The workqueue subsystem doesn't know its best default value, let the system manager or the other subsystem set it when needed. Changed from V8: merge the calculating code for the attrs of the default pwq together. minor change the code&comments for saving the user configured attrs. remove unnecessary list_del(). minor update the comment of wq_calc_node_cpumask(). update the comment of workqueue_set_unbound_cpumask(); Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Original-patch-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-30 09:16:12 +00:00
* different from the default pwq's, we need to compare it to @pwq's
* and create a new one if they don't match. If the target cpumask
* equals the default pwq's, the default pwq should be used.
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
*/
workqueue: Allow modifying low level unbound workqueue cpumask Allow to modify the low-level unbound workqueues cpumask through sysfs. This is performed by traversing the entire workqueue list and calling apply_wqattrs_prepare() on the unbound workqueues with the new low level mask. Only after all the preparation are done, we commit them all together. Ordered workqueues are ignored from the low level unbound workqueue cpumask, it will be handled in near future. All the (default & per-node) pwqs are mandatorily controlled by the low level cpumask. If the user configured cpumask doesn't overlap with the low level cpumask, the low level cpumask will be used for the wq instead. The comment of wq_calc_node_cpumask() is updated and explicitly requires that its first argument should be the attrs of the default pwq. The default wq_unbound_cpumask is cpu_possible_mask. The workqueue subsystem doesn't know its best default value, let the system manager or the other subsystem set it when needed. Changed from V8: merge the calculating code for the attrs of the default pwq together. minor change the code&comments for saving the user configured attrs. remove unnecessary list_del(). minor update the comment of wq_calc_node_cpumask(). update the comment of workqueue_set_unbound_cpumask(); Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Original-patch-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-30 09:16:12 +00:00
if (wq_calc_node_cpumask(wq->dfl_pwq->pool->attrs, node, cpu_off, cpumask)) {
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
if (cpumask_equal(cpumask, pwq->pool->attrs->cpumask))
return;
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
} else {
goto use_dfl_pwq;
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
}
/* create a new pwq */
pwq = alloc_unbound_pwq(wq, target_attrs);
if (!pwq) {
pr_warn("workqueue: allocation failed while updating NUMA affinity of \"%s\"\n",
wq->name);
goto use_dfl_pwq;
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
}
/* Install the new pwq. */
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
mutex_lock(&wq->mutex);
old_pwq = numa_pwq_tbl_install(wq, node, pwq);
goto out_unlock;
use_dfl_pwq:
mutex_lock(&wq->mutex);
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
spin_lock_irq(&wq->dfl_pwq->pool->lock);
get_pwq(wq->dfl_pwq);
spin_unlock_irq(&wq->dfl_pwq->pool->lock);
old_pwq = numa_pwq_tbl_install(wq, node, wq->dfl_pwq);
out_unlock:
mutex_unlock(&wq->mutex);
put_pwq_unlocked(old_pwq);
}
static int alloc_and_link_pwqs(struct workqueue_struct *wq)
{
bool highpri = wq->flags & WQ_HIGHPRI;
int cpu, ret;
if (!(wq->flags & WQ_UNBOUND)) {
wq->cpu_pwqs = alloc_percpu(struct pool_workqueue);
if (!wq->cpu_pwqs)
return -ENOMEM;
for_each_possible_cpu(cpu) {
struct pool_workqueue *pwq =
per_cpu_ptr(wq->cpu_pwqs, cpu);
struct worker_pool *cpu_pools =
per_cpu(cpu_worker_pools, cpu);
init_pwq(pwq, wq, &cpu_pools[highpri]);
mutex_lock(&wq->mutex);
link_pwq(pwq);
mutex_unlock(&wq->mutex);
}
return 0;
} else if (wq->flags & __WQ_ORDERED) {
ret = apply_workqueue_attrs(wq, ordered_wq_attrs[highpri]);
/* there should only be single pwq for ordering guarantee */
WARN(!ret && (wq->pwqs.next != &wq->dfl_pwq->pwqs_node ||
wq->pwqs.prev != &wq->dfl_pwq->pwqs_node),
"ordering guarantee broken for workqueue %s\n", wq->name);
return ret;
} else {
return apply_workqueue_attrs(wq, unbound_std_wq_attrs[highpri]);
}
}
static int wq_clamp_max_active(int max_active, unsigned int flags,
const char *name)
{
int lim = flags & WQ_UNBOUND ? WQ_UNBOUND_MAX_ACTIVE : WQ_MAX_ACTIVE;
if (max_active < 1 || max_active > lim)
pr_warn("workqueue: max_active %d requested for %s is out of range, clamping between %d and %d\n",
max_active, name, 1, lim);
return clamp_val(max_active, 1, lim);
}
struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
unsigned int flags,
int max_active,
struct lock_class_key *key,
const char *lock_name, ...)
{
size_t tbl_size = 0;
va_list args;
struct workqueue_struct *wq;
struct pool_workqueue *pwq;
/* see the comment above the definition of WQ_POWER_EFFICIENT */
if ((flags & WQ_POWER_EFFICIENT) && wq_power_efficient)
flags |= WQ_UNBOUND;
/* allocate wq and format name */
if (flags & WQ_UNBOUND)
tbl_size = nr_node_ids * sizeof(wq->numa_pwq_tbl[0]);
wq = kzalloc(sizeof(*wq) + tbl_size, GFP_KERNEL);
if (!wq)
return NULL;
if (flags & WQ_UNBOUND) {
wq->unbound_attrs = alloc_workqueue_attrs(GFP_KERNEL);
if (!wq->unbound_attrs)
goto err_free_wq;
}
va_start(args, lock_name);
vsnprintf(wq->name, sizeof(wq->name), fmt, args);
va_end(args);
max_active = max_active ?: WQ_DFL_ACTIVE;
max_active = wq_clamp_max_active(max_active, flags, wq->name);
/* init wq */
wq->flags = flags;
wq->saved_max_active = max_active;
mutex_init(&wq->mutex);
atomic_set(&wq->nr_pwqs_to_flush, 0);
INIT_LIST_HEAD(&wq->pwqs);
workqueue: reimplement workqueue flushing using color coded works Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:11 +00:00
INIT_LIST_HEAD(&wq->flusher_queue);
INIT_LIST_HEAD(&wq->flusher_overflow);
INIT_LIST_HEAD(&wq->maydays);
lockdep_init_map(&wq->lockdep_map, lock_name, key, 0);
INIT_LIST_HEAD(&wq->list);
if (alloc_and_link_pwqs(wq) < 0)
goto err_free_wq;
/*
* Workqueues which may be used during memory reclaim should
* have a rescuer to guarantee forward progress.
*/
if (flags & WQ_MEM_RECLAIM) {
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
struct worker *rescuer;
rescuer = alloc_worker(NUMA_NO_NODE);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
if (!rescuer)
goto err_destroy;
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
rescuer->rescue_wq = wq;
rescuer->task = kthread_create(rescuer_thread, rescuer, "%s",
wq->name);
if (IS_ERR(rescuer->task)) {
kfree(rescuer);
goto err_destroy;
}
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
wq->rescuer = rescuer;
kthread_bind_mask(rescuer->task, cpu_possible_mask);
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
wake_up_process(rescuer->task);
}
if ((wq->flags & WQ_SYSFS) && workqueue_sysfs_register(wq))
goto err_destroy;
/*
* wq_pool_mutex protects global freeze state and workqueues list.
* Grab it, adjust max_active and add the new @wq to workqueues
* list.
*/
mutex_lock(&wq_pool_mutex);
mutex_lock(&wq->mutex);
for_each_pwq(pwq, wq)
pwq_adjust_max_active(pwq);
mutex_unlock(&wq->mutex);
list_add_tail_rcu(&wq->list, &workqueues);
mutex_unlock(&wq_pool_mutex);
return wq;
err_free_wq:
free_workqueue_attrs(wq->unbound_attrs);
kfree(wq);
return NULL;
err_destroy:
destroy_workqueue(wq);
return NULL;
}
EXPORT_SYMBOL_GPL(__alloc_workqueue_key);
/**
* destroy_workqueue - safely terminate a workqueue
* @wq: target workqueue
*
* Safely destroy a workqueue. All work currently pending will be done first.
*/
void destroy_workqueue(struct workqueue_struct *wq)
{
struct pool_workqueue *pwq;
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
int node;
/* drain it before proceeding with destruction */
drain_workqueue(wq);
/* sanity checks */
mutex_lock(&wq->mutex);
for_each_pwq(pwq, wq) {
int i;
for (i = 0; i < WORK_NR_COLORS; i++) {
if (WARN_ON(pwq->nr_in_flight[i])) {
mutex_unlock(&wq->mutex);
show_workqueue_state();
return;
}
}
workqueue: avoid false negative WARN_ON() in destroy_workqueue() destroy_workqueue() performs several sanity checks before proceeding with destruction of a workqueue. One of the checks verifies that refcnt of each pwq (pool_workqueue) is over 1 as at that point there should be no in-flight work items and the only holder of pwq refs is the workqueue itself. This worked fine as a workqueue used to hold only one reference to its pwqs; however, since 4c16bd327c ("workqueue: implement NUMA affinity for unbound workqueues"), a workqueue may hold multiple references to its default pwq triggering this sanity check spuriously. Fix it by not triggering the pwq->refcnt assertion on default pwqs. An example spurious WARN trigger follows. WARNING: at kernel/workqueue.c:4201 destroy_workqueue+0x6a/0x13e() Hardware name: 4286C12 Modules linked in: sdhci_pci sdhci mmc_core usb_storage i915 drm_kms_helper drm i2c_algo_bit i2c_core video Pid: 361, comm: umount Not tainted 3.9.0-rc5+ #29 Call Trace: [<c04314a7>] warn_slowpath_common+0x7c/0x93 [<c04314e0>] warn_slowpath_null+0x22/0x24 [<c044796a>] destroy_workqueue+0x6a/0x13e [<c056dc01>] ext4_put_super+0x43/0x2c4 [<c04fb7b8>] generic_shutdown_super+0x4b/0xb9 [<c04fb848>] kill_block_super+0x22/0x60 [<c04fb960>] deactivate_locked_super+0x2f/0x56 [<c04fc41b>] deactivate_super+0x2e/0x31 [<c050f1e6>] mntput_no_expire+0x103/0x108 [<c050fdce>] sys_umount+0x2a2/0x2c4 [<c050fe0e>] sys_oldumount+0x1e/0x20 [<c085ba4d>] sysenter_do_call+0x12/0x38 tj: Rewrote description. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Fengguang Wu <fengguang.wu@intel.com>
2013-04-04 02:05:38 +00:00
if (WARN_ON((pwq != wq->dfl_pwq) && (pwq->refcnt > 1)) ||
WARN_ON(pwq->nr_active) ||
WARN_ON(!list_empty(&pwq->delayed_works))) {
mutex_unlock(&wq->mutex);
show_workqueue_state();
return;
}
}
mutex_unlock(&wq->mutex);
/*
* wq list is used to freeze wq, remove from list after
* flushing is complete in case freeze races us.
*/
mutex_lock(&wq_pool_mutex);
list_del_rcu(&wq->list);
mutex_unlock(&wq_pool_mutex);
workqueue_sysfs_unregister(wq);
if (wq->rescuer)
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
kthread_stop(wq->rescuer->task);
if (!(wq->flags & WQ_UNBOUND)) {
/*
* The base ref is never dropped on per-cpu pwqs. Directly
* schedule RCU free.
*/
call_rcu_sched(&wq->rcu, rcu_free_wq);
} else {
/*
* We're the sole accessor of @wq at this point. Directly
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
* access numa_pwq_tbl[] and dfl_pwq to put the base refs.
* @wq will be freed when the last pwq is released.
*/
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
for_each_node(node) {
pwq = rcu_access_pointer(wq->numa_pwq_tbl[node]);
RCU_INIT_POINTER(wq->numa_pwq_tbl[node], NULL);
put_pwq_unlocked(pwq);
}
/*
* Put dfl_pwq. @wq may be freed any time after dfl_pwq is
* put. Don't access it afterwards.
*/
pwq = wq->dfl_pwq;
wq->dfl_pwq = NULL;
put_pwq_unlocked(pwq);
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
}
}
EXPORT_SYMBOL_GPL(destroy_workqueue);
/**
* workqueue_set_max_active - adjust max_active of a workqueue
* @wq: target workqueue
* @max_active: new max_active value.
*
* Set max_active of @wq to @max_active.
*
* CONTEXT:
* Don't call from IRQ context.
*/
void workqueue_set_max_active(struct workqueue_struct *wq, int max_active)
{
struct pool_workqueue *pwq;
/* disallow meddling with max_active for ordered workqueues */
if (WARN_ON(wq->flags & __WQ_ORDERED))
return;
max_active = wq_clamp_max_active(max_active, wq->flags, wq->name);
mutex_lock(&wq->mutex);
wq->saved_max_active = max_active;
for_each_pwq(pwq, wq)
pwq_adjust_max_active(pwq);
mutex_unlock(&wq->mutex);
}
EXPORT_SYMBOL_GPL(workqueue_set_max_active);
/**
* current_is_workqueue_rescuer - is %current workqueue rescuer?
*
* Determine whether %current is a workqueue rescuer. Can be used from
* work functions to determine whether it's being run off the rescuer task.
*
* Return: %true if %current is a workqueue rescuer. %false otherwise.
*/
bool current_is_workqueue_rescuer(void)
{
struct worker *worker = current_wq_worker();
return worker && worker->rescue_wq;
}
/**
* workqueue_congested - test whether a workqueue is congested
* @cpu: CPU in question
* @wq: target workqueue
*
* Test whether @wq's cpu workqueue for @cpu is congested. There is
* no synchronization around this function and the test result is
* unreliable and only useful as advisory hints or for debugging.
*
workqueue: workqueue_congested() shouldn't translate WORK_CPU_UNBOUND into node number df2d5ae499 ("workqueue: map an unbound workqueues to multiple per-node pool_workqueues") made unbound workqueues to map to multiple per-node pool_workqueues and accordingly updated workqueue_contested() so that, for unbound workqueues, it maps the specified @cpu to the NUMA node number to obtain the matching pool_workqueue to query the congested state. Before this change, workqueue_congested() ignored @cpu for unbound workqueues as there was only one pool_workqueue and some users (fscache) called it with WORK_CPU_UNBOUND. After the commit, this causes the following oops as WORK_CPU_UNBOUND gets translated to garbage by cpu_to_node(). BUG: unable to handle kernel paging request at ffff8803598d98b8 IP: [<ffffffff81043b7e>] unbound_pwq_by_node+0xa1/0xfa PGD 2421067 PUD 0 Oops: 0000 [#1] SMP CPU: 1 PID: 2689 Comm: cat Tainted: GF 3.9.0-fsdevel+ #4 task: ffff88003d801040 ti: ffff880025806000 task.ti: ffff880025806000 RIP: 0010:[<ffffffff81043b7e>] [<ffffffff81043b7e>] unbound_pwq_by_node+0xa1/0xfa RSP: 0018:ffff880025807ad8 EFLAGS: 00010202 RAX: 0000000000000001 RBX: ffff8800388a2400 RCX: 0000000000000003 RDX: ffff880025807fd8 RSI: ffffffff81a31420 RDI: ffff88003d8016e0 RBP: ffff880025807ae8 R08: ffff88003d801730 R09: ffffffffa00b4898 R10: ffffffff81044217 R11: ffff88003d801040 R12: 0000000064206e97 R13: ffff880036059d98 R14: ffff880038cc8080 R15: ffff880038cc82d0 FS: 00007f21afd9c740(0000) GS:ffff88003d100000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b CR2: ffff8803598d98b8 CR3: 000000003df49000 CR4: 00000000000007e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Stack: ffff8800388a2400 0000000000000002 ffff880025807b18 ffffffff810442ce ffffffff81044217 ffff880000000002 ffff8800371b4080 ffff88003d112ec0 ffff880025807b38 ffffffffa00810b0 ffff880036059d88 ffff880036059be8 Call Trace: [<ffffffff810442ce>] workqueue_congested+0xb7/0x12c [<ffffffffa00810b0>] fscache_enqueue_object+0xb2/0xe8 [fscache] [<ffffffffa007facd>] __fscache_acquire_cookie+0x3b9/0x56c [fscache] [<ffffffffa00ad8fe>] nfs_fscache_set_inode_cookie+0xee/0x132 [nfs] [<ffffffffa009e112>] do_open+0x9/0xd [nfs] [<ffffffff810e804a>] do_dentry_open+0x175/0x24b [<ffffffff810e8298>] finish_open+0x41/0x51 Fix it by using smp_processor_id() if @cpu is WORK_CPU_UNBOUND. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: David Howells <dhowells@redhat.com> Tested-and-Acked-by: David Howells <dhowells@redhat.com>
2013-05-10 18:10:17 +00:00
* If @cpu is WORK_CPU_UNBOUND, the test is performed on the local CPU.
* Note that both per-cpu and unbound workqueues may be associated with
* multiple pool_workqueues which have separate congested states. A
* workqueue being congested on one CPU doesn't mean the workqueue is also
* contested on other CPUs / NUMA nodes.
*
* Return:
* %true if congested, %false otherwise.
*/
bool workqueue_congested(int cpu, struct workqueue_struct *wq)
{
struct pool_workqueue *pwq;
bool ret;
rcu_read_lock_sched();
workqueue: workqueue_congested() shouldn't translate WORK_CPU_UNBOUND into node number df2d5ae499 ("workqueue: map an unbound workqueues to multiple per-node pool_workqueues") made unbound workqueues to map to multiple per-node pool_workqueues and accordingly updated workqueue_contested() so that, for unbound workqueues, it maps the specified @cpu to the NUMA node number to obtain the matching pool_workqueue to query the congested state. Before this change, workqueue_congested() ignored @cpu for unbound workqueues as there was only one pool_workqueue and some users (fscache) called it with WORK_CPU_UNBOUND. After the commit, this causes the following oops as WORK_CPU_UNBOUND gets translated to garbage by cpu_to_node(). BUG: unable to handle kernel paging request at ffff8803598d98b8 IP: [<ffffffff81043b7e>] unbound_pwq_by_node+0xa1/0xfa PGD 2421067 PUD 0 Oops: 0000 [#1] SMP CPU: 1 PID: 2689 Comm: cat Tainted: GF 3.9.0-fsdevel+ #4 task: ffff88003d801040 ti: ffff880025806000 task.ti: ffff880025806000 RIP: 0010:[<ffffffff81043b7e>] [<ffffffff81043b7e>] unbound_pwq_by_node+0xa1/0xfa RSP: 0018:ffff880025807ad8 EFLAGS: 00010202 RAX: 0000000000000001 RBX: ffff8800388a2400 RCX: 0000000000000003 RDX: ffff880025807fd8 RSI: ffffffff81a31420 RDI: ffff88003d8016e0 RBP: ffff880025807ae8 R08: ffff88003d801730 R09: ffffffffa00b4898 R10: ffffffff81044217 R11: ffff88003d801040 R12: 0000000064206e97 R13: ffff880036059d98 R14: ffff880038cc8080 R15: ffff880038cc82d0 FS: 00007f21afd9c740(0000) GS:ffff88003d100000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b CR2: ffff8803598d98b8 CR3: 000000003df49000 CR4: 00000000000007e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Stack: ffff8800388a2400 0000000000000002 ffff880025807b18 ffffffff810442ce ffffffff81044217 ffff880000000002 ffff8800371b4080 ffff88003d112ec0 ffff880025807b38 ffffffffa00810b0 ffff880036059d88 ffff880036059be8 Call Trace: [<ffffffff810442ce>] workqueue_congested+0xb7/0x12c [<ffffffffa00810b0>] fscache_enqueue_object+0xb2/0xe8 [fscache] [<ffffffffa007facd>] __fscache_acquire_cookie+0x3b9/0x56c [fscache] [<ffffffffa00ad8fe>] nfs_fscache_set_inode_cookie+0xee/0x132 [nfs] [<ffffffffa009e112>] do_open+0x9/0xd [nfs] [<ffffffff810e804a>] do_dentry_open+0x175/0x24b [<ffffffff810e8298>] finish_open+0x41/0x51 Fix it by using smp_processor_id() if @cpu is WORK_CPU_UNBOUND. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: David Howells <dhowells@redhat.com> Tested-and-Acked-by: David Howells <dhowells@redhat.com>
2013-05-10 18:10:17 +00:00
if (cpu == WORK_CPU_UNBOUND)
cpu = smp_processor_id();
if (!(wq->flags & WQ_UNBOUND))
pwq = per_cpu_ptr(wq->cpu_pwqs, cpu);
else
pwq = unbound_pwq_by_node(wq, cpu_to_node(cpu));
ret = !list_empty(&pwq->delayed_works);
rcu_read_unlock_sched();
return ret;
}
EXPORT_SYMBOL_GPL(workqueue_congested);
/**
* work_busy - test whether a work is currently pending or running
* @work: the work to be tested
*
* Test whether @work is currently pending or running. There is no
* synchronization around this function and the test result is
* unreliable and only useful as advisory hints or for debugging.
*
* Return:
* OR'd bitmask of WORK_BUSY_* bits.
*/
unsigned int work_busy(struct work_struct *work)
{
struct worker_pool *pool;
unsigned long flags;
unsigned int ret = 0;
if (work_pending(work))
ret |= WORK_BUSY_PENDING;
local_irq_save(flags);
pool = get_work_pool(work);
if (pool) {
spin_lock(&pool->lock);
if (find_worker_executing_work(pool, work))
ret |= WORK_BUSY_RUNNING;
spin_unlock(&pool->lock);
}
local_irq_restore(flags);
return ret;
}
EXPORT_SYMBOL_GPL(work_busy);
workqueue: include workqueue info when printing debug dump of a worker task One of the problems that arise when converting dedicated custom threadpool to workqueue is that the shared worker pool used by workqueue anonimizes each worker making it more difficult to identify what the worker was doing on which target from the output of sysrq-t or debug dump from oops, BUG() and friends. This patch implements set_worker_desc() which can be called from any workqueue work function to set its description. When the worker task is dumped for whatever reason - sysrq-t, WARN, BUG, oops, lockdep assertion and so on - the description will be printed out together with the workqueue name and the worker function pointer. The printing side is implemented by print_worker_info() which is called from functions in task dump paths - sched_show_task() and dump_stack_print_info(). print_worker_info() can be safely called on any task in any state as long as the task struct itself is accessible. It uses probe_*() functions to access worker fields. It may print garbage if something went very wrong, but it wouldn't cause (another) oops. The description is currently limited to 24bytes including the terminating \0. worker->desc_valid and workder->desc[] are added and the 64 bytes marker which was already incorrect before adding the new fields is moved to the correct position. Here's an example dump with writeback updated to set the bdi name as worker desc. Hardware name: Bochs Modules linked in: Pid: 7, comm: kworker/u9:0 Not tainted 3.9.0-rc1-work+ #1 Workqueue: writeback bdi_writeback_workfn (flush-8:0) ffffffff820a3ab0 ffff88000f6e9cb8 ffffffff81c61845 ffff88000f6e9cf8 ffffffff8108f50f 0000000000000000 0000000000000000 ffff88000cde16b0 ffff88000cde1aa8 ffff88001ee19240 ffff88000f6e9fd8 ffff88000f6e9d08 Call Trace: [<ffffffff81c61845>] dump_stack+0x19/0x1b [<ffffffff8108f50f>] warn_slowpath_common+0x7f/0xc0 [<ffffffff8108f56a>] warn_slowpath_null+0x1a/0x20 [<ffffffff81200150>] bdi_writeback_workfn+0x2a0/0x3b0 ... Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com> Acked-by: Jan Kara <jack@suse.cz> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Dave Chinner <david@fromorbit.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-04-30 22:27:22 +00:00
/**
* set_worker_desc - set description for the current work item
* @fmt: printf-style format string
* @...: arguments for the format string
*
* This function can be called by a running work function to describe what
* the work item is about. If the worker task gets dumped, this
* information will be printed out together to help debugging. The
* description can be at most WORKER_DESC_LEN including the trailing '\0'.
*/
void set_worker_desc(const char *fmt, ...)
{
struct worker *worker = current_wq_worker();
va_list args;
if (worker) {
va_start(args, fmt);
vsnprintf(worker->desc, sizeof(worker->desc), fmt, args);
va_end(args);
worker->desc_valid = true;
}
}
/**
* print_worker_info - print out worker information and description
* @log_lvl: the log level to use when printing
* @task: target task
*
* If @task is a worker and currently executing a work item, print out the
* name of the workqueue being serviced and worker description set with
* set_worker_desc() by the currently executing work item.
*
* This function can be safely called on any task as long as the
* task_struct itself is accessible. While safe, this function isn't
* synchronized and may print out mixups or garbages of limited length.
*/
void print_worker_info(const char *log_lvl, struct task_struct *task)
{
work_func_t *fn = NULL;
char name[WQ_NAME_LEN] = { };
char desc[WORKER_DESC_LEN] = { };
struct pool_workqueue *pwq = NULL;
struct workqueue_struct *wq = NULL;
bool desc_valid = false;
struct worker *worker;
if (!(task->flags & PF_WQ_WORKER))
return;
/*
* This function is called without any synchronization and @task
* could be in any state. Be careful with dereferences.
*/
worker = probe_kthread_data(task);
/*
* Carefully copy the associated workqueue's workfn and name. Keep
* the original last '\0' in case the original contains garbage.
*/
probe_kernel_read(&fn, &worker->current_func, sizeof(fn));
probe_kernel_read(&pwq, &worker->current_pwq, sizeof(pwq));
probe_kernel_read(&wq, &pwq->wq, sizeof(wq));
probe_kernel_read(name, wq->name, sizeof(name) - 1);
/* copy worker description */
probe_kernel_read(&desc_valid, &worker->desc_valid, sizeof(desc_valid));
if (desc_valid)
probe_kernel_read(desc, worker->desc, sizeof(desc) - 1);
if (fn || name[0] || desc[0]) {
printk("%sWorkqueue: %s %pf", log_lvl, name, fn);
if (desc[0])
pr_cont(" (%s)", desc);
pr_cont("\n");
}
}
workqueue: dump workqueues on sysrq-t Workqueues are used extensively throughout the kernel but sometimes it's difficult to debug stalls involving work items because visibility into its inner workings is fairly limited. Although sysrq-t task dump annotates each active worker task with the information on the work item being executed, it is challenging to find out which work items are pending or delayed on which queues and how pools are being managed. This patch implements show_workqueue_state() which dumps all busy workqueues and pools and is called from the sysrq-t handler. At the end of sysrq-t dump, something like the following is printed. Showing busy workqueues and worker pools: ... workqueue filler_wq: flags=0x0 pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=2/256 in-flight: 491:filler_workfn, 507:filler_workfn pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=2/256 in-flight: 501:filler_workfn pending: filler_workfn ... workqueue test_wq: flags=0x8 pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=1/1 in-flight: 510(RESCUER):test_workfn BAR(69) BAR(500) delayed: test_workfn1 BAR(492), test_workfn2 ... pool 0: cpus=0 node=0 flags=0x0 nice=0 workers=2 manager: 137 pool 2: cpus=1 node=0 flags=0x0 nice=0 workers=3 manager: 469 pool 3: cpus=1 node=0 flags=0x0 nice=-20 workers=2 idle: 16 pool 8: cpus=0-3 flags=0x4 nice=0 workers=2 manager: 62 The above shows that test_wq is executing test_workfn() on pid 510 which is the rescuer and also that there are two tasks 69 and 500 waiting for the work item to finish in flush_work(). As test_wq has max_active of 1, there are two work items for test_workfn1() and test_workfn2() which are delayed till the current work item is finished. In addition, pid 492 is flushing test_workfn1(). The work item for test_workfn() is being executed on pwq of pool 2 which is the normal priority per-cpu pool for CPU 1. The pool has three workers, two of which are executing filler_workfn() for filler_wq and the last one is assuming the manager role trying to create more workers. This extra workqueue state dump will hopefully help chasing down hangs involving workqueues. v3: cpulist_pr_cont() replaced with "%*pbl" printf formatting. v2: As suggested by Andrew, minor formatting change in pr_cont_work(), printk()'s replaced with pr_info()'s, and cpumask printing now uses cpulist_pr_cont(). Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> CC: Ingo Molnar <mingo@redhat.com>
2015-03-09 13:22:28 +00:00
static void pr_cont_pool_info(struct worker_pool *pool)
{
pr_cont(" cpus=%*pbl", nr_cpumask_bits, pool->attrs->cpumask);
if (pool->node != NUMA_NO_NODE)
pr_cont(" node=%d", pool->node);
pr_cont(" flags=0x%x nice=%d", pool->flags, pool->attrs->nice);
}
static void pr_cont_work(bool comma, struct work_struct *work)
{
if (work->func == wq_barrier_func) {
struct wq_barrier *barr;
barr = container_of(work, struct wq_barrier, work);
pr_cont("%s BAR(%d)", comma ? "," : "",
task_pid_nr(barr->task));
} else {
pr_cont("%s %pf", comma ? "," : "", work->func);
}
}
static void show_pwq(struct pool_workqueue *pwq)
{
struct worker_pool *pool = pwq->pool;
struct work_struct *work;
struct worker *worker;
bool has_in_flight = false, has_pending = false;
int bkt;
pr_info(" pwq %d:", pool->id);
pr_cont_pool_info(pool);
pr_cont(" active=%d/%d%s\n", pwq->nr_active, pwq->max_active,
!list_empty(&pwq->mayday_node) ? " MAYDAY" : "");
hash_for_each(pool->busy_hash, bkt, worker, hentry) {
if (worker->current_pwq == pwq) {
has_in_flight = true;
break;
}
}
if (has_in_flight) {
bool comma = false;
pr_info(" in-flight:");
hash_for_each(pool->busy_hash, bkt, worker, hentry) {
if (worker->current_pwq != pwq)
continue;
pr_cont("%s %d%s:%pf", comma ? "," : "",
task_pid_nr(worker->task),
worker == pwq->wq->rescuer ? "(RESCUER)" : "",
worker->current_func);
list_for_each_entry(work, &worker->scheduled, entry)
pr_cont_work(false, work);
comma = true;
}
pr_cont("\n");
}
list_for_each_entry(work, &pool->worklist, entry) {
if (get_work_pwq(work) == pwq) {
has_pending = true;
break;
}
}
if (has_pending) {
bool comma = false;
pr_info(" pending:");
list_for_each_entry(work, &pool->worklist, entry) {
if (get_work_pwq(work) != pwq)
continue;
pr_cont_work(comma, work);
comma = !(*work_data_bits(work) & WORK_STRUCT_LINKED);
}
pr_cont("\n");
}
if (!list_empty(&pwq->delayed_works)) {
bool comma = false;
pr_info(" delayed:");
list_for_each_entry(work, &pwq->delayed_works, entry) {
pr_cont_work(comma, work);
comma = !(*work_data_bits(work) & WORK_STRUCT_LINKED);
}
pr_cont("\n");
}
}
/**
* show_workqueue_state - dump workqueue state
*
* Called from a sysrq handler or try_to_freeze_tasks() and prints out
* all busy workqueues and pools.
workqueue: dump workqueues on sysrq-t Workqueues are used extensively throughout the kernel but sometimes it's difficult to debug stalls involving work items because visibility into its inner workings is fairly limited. Although sysrq-t task dump annotates each active worker task with the information on the work item being executed, it is challenging to find out which work items are pending or delayed on which queues and how pools are being managed. This patch implements show_workqueue_state() which dumps all busy workqueues and pools and is called from the sysrq-t handler. At the end of sysrq-t dump, something like the following is printed. Showing busy workqueues and worker pools: ... workqueue filler_wq: flags=0x0 pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=2/256 in-flight: 491:filler_workfn, 507:filler_workfn pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=2/256 in-flight: 501:filler_workfn pending: filler_workfn ... workqueue test_wq: flags=0x8 pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=1/1 in-flight: 510(RESCUER):test_workfn BAR(69) BAR(500) delayed: test_workfn1 BAR(492), test_workfn2 ... pool 0: cpus=0 node=0 flags=0x0 nice=0 workers=2 manager: 137 pool 2: cpus=1 node=0 flags=0x0 nice=0 workers=3 manager: 469 pool 3: cpus=1 node=0 flags=0x0 nice=-20 workers=2 idle: 16 pool 8: cpus=0-3 flags=0x4 nice=0 workers=2 manager: 62 The above shows that test_wq is executing test_workfn() on pid 510 which is the rescuer and also that there are two tasks 69 and 500 waiting for the work item to finish in flush_work(). As test_wq has max_active of 1, there are two work items for test_workfn1() and test_workfn2() which are delayed till the current work item is finished. In addition, pid 492 is flushing test_workfn1(). The work item for test_workfn() is being executed on pwq of pool 2 which is the normal priority per-cpu pool for CPU 1. The pool has three workers, two of which are executing filler_workfn() for filler_wq and the last one is assuming the manager role trying to create more workers. This extra workqueue state dump will hopefully help chasing down hangs involving workqueues. v3: cpulist_pr_cont() replaced with "%*pbl" printf formatting. v2: As suggested by Andrew, minor formatting change in pr_cont_work(), printk()'s replaced with pr_info()'s, and cpumask printing now uses cpulist_pr_cont(). Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> CC: Ingo Molnar <mingo@redhat.com>
2015-03-09 13:22:28 +00:00
*/
void show_workqueue_state(void)
{
struct workqueue_struct *wq;
struct worker_pool *pool;
unsigned long flags;
int pi;
rcu_read_lock_sched();
pr_info("Showing busy workqueues and worker pools:\n");
list_for_each_entry_rcu(wq, &workqueues, list) {
struct pool_workqueue *pwq;
bool idle = true;
for_each_pwq(pwq, wq) {
if (pwq->nr_active || !list_empty(&pwq->delayed_works)) {
idle = false;
break;
}
}
if (idle)
continue;
pr_info("workqueue %s: flags=0x%x\n", wq->name, wq->flags);
for_each_pwq(pwq, wq) {
spin_lock_irqsave(&pwq->pool->lock, flags);
if (pwq->nr_active || !list_empty(&pwq->delayed_works))
show_pwq(pwq);
spin_unlock_irqrestore(&pwq->pool->lock, flags);
}
}
for_each_pool(pool, pi) {
struct worker *worker;
bool first = true;
spin_lock_irqsave(&pool->lock, flags);
if (pool->nr_workers == pool->nr_idle)
goto next_pool;
pr_info("pool %d:", pool->id);
pr_cont_pool_info(pool);
workqueue: implement lockup detector Workqueue stalls can happen from a variety of usage bugs such as missing WQ_MEM_RECLAIM flag or concurrency managed work item indefinitely staying RUNNING. These stalls can be extremely difficult to hunt down because the usual warning mechanisms can't detect workqueue stalls and the internal state is pretty opaque. To alleviate the situation, this patch implements workqueue lockup detector. It periodically monitors all worker_pools periodically and, if any pool failed to make forward progress longer than the threshold duration, triggers warning and dumps workqueue state as follows. BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 31s! Showing busy workqueues and worker pools: workqueue events: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=17/256 pending: monkey_wrench_fn, e1000_watchdog, cache_reap, vmstat_shepherd, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, cgroup_release_agent workqueue events_power_efficient: flags=0x80 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=2/256 pending: check_lifetime, neigh_periodic_work workqueue cgroup_pidlist_destroy: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/1 pending: cgroup_pidlist_destroy_work_fn ... The detection mechanism is controller through kernel parameter workqueue.watchdog_thresh and can be updated at runtime through the sysfs module parameter file. v2: Decoupled from softlockup control knobs. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Don Zickus <dzickus@redhat.com> Cc: Ulrich Obergfell <uobergfe@redhat.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Chris Mason <clm@fb.com> Cc: Andrew Morton <akpm@linux-foundation.org>
2015-12-08 16:28:04 +00:00
pr_cont(" hung=%us workers=%d",
jiffies_to_msecs(jiffies - pool->watchdog_ts) / 1000,
pool->nr_workers);
workqueue: dump workqueues on sysrq-t Workqueues are used extensively throughout the kernel but sometimes it's difficult to debug stalls involving work items because visibility into its inner workings is fairly limited. Although sysrq-t task dump annotates each active worker task with the information on the work item being executed, it is challenging to find out which work items are pending or delayed on which queues and how pools are being managed. This patch implements show_workqueue_state() which dumps all busy workqueues and pools and is called from the sysrq-t handler. At the end of sysrq-t dump, something like the following is printed. Showing busy workqueues and worker pools: ... workqueue filler_wq: flags=0x0 pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=2/256 in-flight: 491:filler_workfn, 507:filler_workfn pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=2/256 in-flight: 501:filler_workfn pending: filler_workfn ... workqueue test_wq: flags=0x8 pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=1/1 in-flight: 510(RESCUER):test_workfn BAR(69) BAR(500) delayed: test_workfn1 BAR(492), test_workfn2 ... pool 0: cpus=0 node=0 flags=0x0 nice=0 workers=2 manager: 137 pool 2: cpus=1 node=0 flags=0x0 nice=0 workers=3 manager: 469 pool 3: cpus=1 node=0 flags=0x0 nice=-20 workers=2 idle: 16 pool 8: cpus=0-3 flags=0x4 nice=0 workers=2 manager: 62 The above shows that test_wq is executing test_workfn() on pid 510 which is the rescuer and also that there are two tasks 69 and 500 waiting for the work item to finish in flush_work(). As test_wq has max_active of 1, there are two work items for test_workfn1() and test_workfn2() which are delayed till the current work item is finished. In addition, pid 492 is flushing test_workfn1(). The work item for test_workfn() is being executed on pwq of pool 2 which is the normal priority per-cpu pool for CPU 1. The pool has three workers, two of which are executing filler_workfn() for filler_wq and the last one is assuming the manager role trying to create more workers. This extra workqueue state dump will hopefully help chasing down hangs involving workqueues. v3: cpulist_pr_cont() replaced with "%*pbl" printf formatting. v2: As suggested by Andrew, minor formatting change in pr_cont_work(), printk()'s replaced with pr_info()'s, and cpumask printing now uses cpulist_pr_cont(). Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> CC: Ingo Molnar <mingo@redhat.com>
2015-03-09 13:22:28 +00:00
if (pool->manager)
pr_cont(" manager: %d",
task_pid_nr(pool->manager->task));
list_for_each_entry(worker, &pool->idle_list, entry) {
pr_cont(" %s%d", first ? "idle: " : "",
task_pid_nr(worker->task));
first = false;
}
pr_cont("\n");
next_pool:
spin_unlock_irqrestore(&pool->lock, flags);
}
rcu_read_unlock_sched();
}
/*
* CPU hotplug.
*
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
* There are two challenges in supporting CPU hotplug. Firstly, there
* are a lot of assumptions on strong associations among work, pwq and
* pool which make migrating pending and scheduled works very
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
* difficult to implement without impacting hot paths. Secondly,
* worker pools serve mix of short, long and very long running works making
workqueue: implement concurrency managed dynamic worker pool Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: Tejun Heo <tj@kernel.org>
2010-06-29 08:07:14 +00:00
* blocked draining impractical.
*
* This is solved by allowing the pools to be disassociated from the CPU
* running as an unbound one and allowing it to be reattached later if the
* cpu comes back online.
*/
static void wq_unbind_fn(struct work_struct *work)
{
int cpu = smp_processor_id();
struct worker_pool *pool;
struct worker *worker;
for_each_cpu_worker_pool(pool, cpu) {
mutex_lock(&pool->attach_mutex);
spin_lock_irq(&pool->lock);
/*
* We've blocked all attach/detach operations. Make all workers
* unbound and set DISASSOCIATED. Before this, all workers
* except for the ones which are still executing works from
* before the last CPU down must be on the cpu. After
* this, they may become diasporas.
*/
for_each_pool_worker(worker, pool)
worker->flags |= WORKER_UNBOUND;
pool->flags |= POOL_DISASSOCIATED;
spin_unlock_irq(&pool->lock);
mutex_unlock(&pool->attach_mutex);
/*
* Call schedule() so that we cross rq->lock and thus can
* guarantee sched callbacks see the %WORKER_UNBOUND flag.
* This is necessary as scheduler callbacks may be invoked
* from other cpus.
*/
schedule();
/*
* Sched callbacks are disabled now. Zap nr_running.
* After this, nr_running stays zero and need_more_worker()
* and keep_working() are always true as long as the
* worklist is not empty. This pool now behaves as an
* unbound (in terms of concurrency management) pool which
* are served by workers tied to the pool.
*/
atomic_set(&pool->nr_running, 0);
/*
* With concurrency management just turned off, a busy
* worker blocking could lead to lengthy stalls. Kick off
* unbound chain execution of currently pending work items.
*/
spin_lock_irq(&pool->lock);
wake_up_worker(pool);
spin_unlock_irq(&pool->lock);
}
}
/**
* rebind_workers - rebind all workers of a pool to the associated CPU
* @pool: pool of interest
*
workqueue: directly restore CPU affinity of workers from CPU_ONLINE Rebinding workers of a per-cpu pool after a CPU comes online involves a lot of back-and-forth mostly because only the task itself could adjust CPU affinity if PF_THREAD_BOUND was set. As CPU_ONLINE itself couldn't adjust affinity, it had to somehow coerce the workers themselves to perform set_cpus_allowed_ptr(). Due to the various states a worker can be in, this led to three different paths a worker may be rebound. worker->rebind_work is queued to busy workers. Idle ones are signaled by unlinking worker->entry and call idle_worker_rebind(). The manager isn't covered by either and implements its own mechanism. PF_THREAD_BOUND has been relaced with PF_NO_SETAFFINITY and CPU_ONLINE itself now can manipulate CPU affinity of workers. This patch replaces the existing rebind mechanism with direct one where CPU_ONLINE iterates over all workers using for_each_pool_worker(), restores CPU affinity, and clears WORKER_UNBOUND. There are a couple subtleties. All bound idle workers should have their runqueues set to that of the bound CPU; however, if the target task isn't running, set_cpus_allowed_ptr() just updates the cpus_allowed mask deferring the actual migration to when the task wakes up. This is worked around by waking up idle workers after restoring CPU affinity before any workers can become bound. Another subtlety is stems from matching @pool->nr_running with the number of running unbound workers. While DISASSOCIATED, all workers are unbound and nr_running is zero. As workers become bound again, nr_running needs to be adjusted accordingly; however, there is no good way to tell whether a given worker is running without poking into scheduler internals. Instead of clearing UNBOUND directly, rebind_workers() replaces UNBOUND with another new NOT_RUNNING flag - REBOUND, which will later be cleared by the workers themselves while preparing for the next round of work item execution. The only change needed for the workers is clearing REBOUND along with PREP. * This patch leaves for_each_busy_worker() without any user. Removed. * idle_worker_rebind(), busy_worker_rebind_fn(), worker->rebind_work and rebind logic in manager_workers() removed. * worker_thread() now looks at WORKER_DIE instead of testing whether @worker->entry is empty to determine whether it needs to do something special as dying is the only special thing now. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 20:45:21 +00:00
* @pool->cpu is coming online. Rebind all workers to the CPU.
*/
static void rebind_workers(struct worker_pool *pool)
{
workqueue: directly restore CPU affinity of workers from CPU_ONLINE Rebinding workers of a per-cpu pool after a CPU comes online involves a lot of back-and-forth mostly because only the task itself could adjust CPU affinity if PF_THREAD_BOUND was set. As CPU_ONLINE itself couldn't adjust affinity, it had to somehow coerce the workers themselves to perform set_cpus_allowed_ptr(). Due to the various states a worker can be in, this led to three different paths a worker may be rebound. worker->rebind_work is queued to busy workers. Idle ones are signaled by unlinking worker->entry and call idle_worker_rebind(). The manager isn't covered by either and implements its own mechanism. PF_THREAD_BOUND has been relaced with PF_NO_SETAFFINITY and CPU_ONLINE itself now can manipulate CPU affinity of workers. This patch replaces the existing rebind mechanism with direct one where CPU_ONLINE iterates over all workers using for_each_pool_worker(), restores CPU affinity, and clears WORKER_UNBOUND. There are a couple subtleties. All bound idle workers should have their runqueues set to that of the bound CPU; however, if the target task isn't running, set_cpus_allowed_ptr() just updates the cpus_allowed mask deferring the actual migration to when the task wakes up. This is worked around by waking up idle workers after restoring CPU affinity before any workers can become bound. Another subtlety is stems from matching @pool->nr_running with the number of running unbound workers. While DISASSOCIATED, all workers are unbound and nr_running is zero. As workers become bound again, nr_running needs to be adjusted accordingly; however, there is no good way to tell whether a given worker is running without poking into scheduler internals. Instead of clearing UNBOUND directly, rebind_workers() replaces UNBOUND with another new NOT_RUNNING flag - REBOUND, which will later be cleared by the workers themselves while preparing for the next round of work item execution. The only change needed for the workers is clearing REBOUND along with PREP. * This patch leaves for_each_busy_worker() without any user. Removed. * idle_worker_rebind(), busy_worker_rebind_fn(), worker->rebind_work and rebind logic in manager_workers() removed. * worker_thread() now looks at WORKER_DIE instead of testing whether @worker->entry is empty to determine whether it needs to do something special as dying is the only special thing now. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 20:45:21 +00:00
struct worker *worker;
lockdep_assert_held(&pool->attach_mutex);
workqueue: directly restore CPU affinity of workers from CPU_ONLINE Rebinding workers of a per-cpu pool after a CPU comes online involves a lot of back-and-forth mostly because only the task itself could adjust CPU affinity if PF_THREAD_BOUND was set. As CPU_ONLINE itself couldn't adjust affinity, it had to somehow coerce the workers themselves to perform set_cpus_allowed_ptr(). Due to the various states a worker can be in, this led to three different paths a worker may be rebound. worker->rebind_work is queued to busy workers. Idle ones are signaled by unlinking worker->entry and call idle_worker_rebind(). The manager isn't covered by either and implements its own mechanism. PF_THREAD_BOUND has been relaced with PF_NO_SETAFFINITY and CPU_ONLINE itself now can manipulate CPU affinity of workers. This patch replaces the existing rebind mechanism with direct one where CPU_ONLINE iterates over all workers using for_each_pool_worker(), restores CPU affinity, and clears WORKER_UNBOUND. There are a couple subtleties. All bound idle workers should have their runqueues set to that of the bound CPU; however, if the target task isn't running, set_cpus_allowed_ptr() just updates the cpus_allowed mask deferring the actual migration to when the task wakes up. This is worked around by waking up idle workers after restoring CPU affinity before any workers can become bound. Another subtlety is stems from matching @pool->nr_running with the number of running unbound workers. While DISASSOCIATED, all workers are unbound and nr_running is zero. As workers become bound again, nr_running needs to be adjusted accordingly; however, there is no good way to tell whether a given worker is running without poking into scheduler internals. Instead of clearing UNBOUND directly, rebind_workers() replaces UNBOUND with another new NOT_RUNNING flag - REBOUND, which will later be cleared by the workers themselves while preparing for the next round of work item execution. The only change needed for the workers is clearing REBOUND along with PREP. * This patch leaves for_each_busy_worker() without any user. Removed. * idle_worker_rebind(), busy_worker_rebind_fn(), worker->rebind_work and rebind logic in manager_workers() removed. * worker_thread() now looks at WORKER_DIE instead of testing whether @worker->entry is empty to determine whether it needs to do something special as dying is the only special thing now. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 20:45:21 +00:00
/*
* Restore CPU affinity of all workers. As all idle workers should
* be on the run-queue of the associated CPU before any local
* wake-ups for concurrency management happen, restore CPU affinity
workqueue: directly restore CPU affinity of workers from CPU_ONLINE Rebinding workers of a per-cpu pool after a CPU comes online involves a lot of back-and-forth mostly because only the task itself could adjust CPU affinity if PF_THREAD_BOUND was set. As CPU_ONLINE itself couldn't adjust affinity, it had to somehow coerce the workers themselves to perform set_cpus_allowed_ptr(). Due to the various states a worker can be in, this led to three different paths a worker may be rebound. worker->rebind_work is queued to busy workers. Idle ones are signaled by unlinking worker->entry and call idle_worker_rebind(). The manager isn't covered by either and implements its own mechanism. PF_THREAD_BOUND has been relaced with PF_NO_SETAFFINITY and CPU_ONLINE itself now can manipulate CPU affinity of workers. This patch replaces the existing rebind mechanism with direct one where CPU_ONLINE iterates over all workers using for_each_pool_worker(), restores CPU affinity, and clears WORKER_UNBOUND. There are a couple subtleties. All bound idle workers should have their runqueues set to that of the bound CPU; however, if the target task isn't running, set_cpus_allowed_ptr() just updates the cpus_allowed mask deferring the actual migration to when the task wakes up. This is worked around by waking up idle workers after restoring CPU affinity before any workers can become bound. Another subtlety is stems from matching @pool->nr_running with the number of running unbound workers. While DISASSOCIATED, all workers are unbound and nr_running is zero. As workers become bound again, nr_running needs to be adjusted accordingly; however, there is no good way to tell whether a given worker is running without poking into scheduler internals. Instead of clearing UNBOUND directly, rebind_workers() replaces UNBOUND with another new NOT_RUNNING flag - REBOUND, which will later be cleared by the workers themselves while preparing for the next round of work item execution. The only change needed for the workers is clearing REBOUND along with PREP. * This patch leaves for_each_busy_worker() without any user. Removed. * idle_worker_rebind(), busy_worker_rebind_fn(), worker->rebind_work and rebind logic in manager_workers() removed. * worker_thread() now looks at WORKER_DIE instead of testing whether @worker->entry is empty to determine whether it needs to do something special as dying is the only special thing now. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 20:45:21 +00:00
* of all workers first and then clear UNBOUND. As we're called
* from CPU_ONLINE, the following shouldn't fail.
*/
for_each_pool_worker(worker, pool)
workqueue: directly restore CPU affinity of workers from CPU_ONLINE Rebinding workers of a per-cpu pool after a CPU comes online involves a lot of back-and-forth mostly because only the task itself could adjust CPU affinity if PF_THREAD_BOUND was set. As CPU_ONLINE itself couldn't adjust affinity, it had to somehow coerce the workers themselves to perform set_cpus_allowed_ptr(). Due to the various states a worker can be in, this led to three different paths a worker may be rebound. worker->rebind_work is queued to busy workers. Idle ones are signaled by unlinking worker->entry and call idle_worker_rebind(). The manager isn't covered by either and implements its own mechanism. PF_THREAD_BOUND has been relaced with PF_NO_SETAFFINITY and CPU_ONLINE itself now can manipulate CPU affinity of workers. This patch replaces the existing rebind mechanism with direct one where CPU_ONLINE iterates over all workers using for_each_pool_worker(), restores CPU affinity, and clears WORKER_UNBOUND. There are a couple subtleties. All bound idle workers should have their runqueues set to that of the bound CPU; however, if the target task isn't running, set_cpus_allowed_ptr() just updates the cpus_allowed mask deferring the actual migration to when the task wakes up. This is worked around by waking up idle workers after restoring CPU affinity before any workers can become bound. Another subtlety is stems from matching @pool->nr_running with the number of running unbound workers. While DISASSOCIATED, all workers are unbound and nr_running is zero. As workers become bound again, nr_running needs to be adjusted accordingly; however, there is no good way to tell whether a given worker is running without poking into scheduler internals. Instead of clearing UNBOUND directly, rebind_workers() replaces UNBOUND with another new NOT_RUNNING flag - REBOUND, which will later be cleared by the workers themselves while preparing for the next round of work item execution. The only change needed for the workers is clearing REBOUND along with PREP. * This patch leaves for_each_busy_worker() without any user. Removed. * idle_worker_rebind(), busy_worker_rebind_fn(), worker->rebind_work and rebind logic in manager_workers() removed. * worker_thread() now looks at WORKER_DIE instead of testing whether @worker->entry is empty to determine whether it needs to do something special as dying is the only special thing now. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 20:45:21 +00:00
WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
pool->attrs->cpumask) < 0);
workqueue: directly restore CPU affinity of workers from CPU_ONLINE Rebinding workers of a per-cpu pool after a CPU comes online involves a lot of back-and-forth mostly because only the task itself could adjust CPU affinity if PF_THREAD_BOUND was set. As CPU_ONLINE itself couldn't adjust affinity, it had to somehow coerce the workers themselves to perform set_cpus_allowed_ptr(). Due to the various states a worker can be in, this led to three different paths a worker may be rebound. worker->rebind_work is queued to busy workers. Idle ones are signaled by unlinking worker->entry and call idle_worker_rebind(). The manager isn't covered by either and implements its own mechanism. PF_THREAD_BOUND has been relaced with PF_NO_SETAFFINITY and CPU_ONLINE itself now can manipulate CPU affinity of workers. This patch replaces the existing rebind mechanism with direct one where CPU_ONLINE iterates over all workers using for_each_pool_worker(), restores CPU affinity, and clears WORKER_UNBOUND. There are a couple subtleties. All bound idle workers should have their runqueues set to that of the bound CPU; however, if the target task isn't running, set_cpus_allowed_ptr() just updates the cpus_allowed mask deferring the actual migration to when the task wakes up. This is worked around by waking up idle workers after restoring CPU affinity before any workers can become bound. Another subtlety is stems from matching @pool->nr_running with the number of running unbound workers. While DISASSOCIATED, all workers are unbound and nr_running is zero. As workers become bound again, nr_running needs to be adjusted accordingly; however, there is no good way to tell whether a given worker is running without poking into scheduler internals. Instead of clearing UNBOUND directly, rebind_workers() replaces UNBOUND with another new NOT_RUNNING flag - REBOUND, which will later be cleared by the workers themselves while preparing for the next round of work item execution. The only change needed for the workers is clearing REBOUND along with PREP. * This patch leaves for_each_busy_worker() without any user. Removed. * idle_worker_rebind(), busy_worker_rebind_fn(), worker->rebind_work and rebind logic in manager_workers() removed. * worker_thread() now looks at WORKER_DIE instead of testing whether @worker->entry is empty to determine whether it needs to do something special as dying is the only special thing now. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 20:45:21 +00:00
spin_lock_irq(&pool->lock);
workqueue: fix rebind bound workers warning ------------[ cut here ]------------ WARNING: CPU: 0 PID: 16 at kernel/workqueue.c:4559 rebind_workers+0x1c0/0x1d0 Modules linked in: CPU: 0 PID: 16 Comm: cpuhp/0 Not tainted 4.6.0-rc4+ #31 Hardware name: IBM IBM System x3550 M4 Server -[7914IUW]-/00Y8603, BIOS -[D7E128FUS-1.40]- 07/23/2013 0000000000000000 ffff881037babb58 ffffffff8139d885 0000000000000010 0000000000000000 0000000000000000 0000000000000000 ffff881037babba8 ffffffff8108505d ffff881037ba0000 000011cf3e7d6e60 0000000000000046 Call Trace: dump_stack+0x89/0xd4 __warn+0xfd/0x120 warn_slowpath_null+0x1d/0x20 rebind_workers+0x1c0/0x1d0 workqueue_cpu_up_callback+0xf5/0x1d0 notifier_call_chain+0x64/0x90 ? trace_hardirqs_on_caller+0xf2/0x220 ? notify_prepare+0x80/0x80 __raw_notifier_call_chain+0xe/0x10 __cpu_notify+0x35/0x50 notify_down_prepare+0x5e/0x80 ? notify_prepare+0x80/0x80 cpuhp_invoke_callback+0x73/0x330 ? __schedule+0x33e/0x8a0 cpuhp_down_callbacks+0x51/0xc0 cpuhp_thread_fun+0xc1/0xf0 smpboot_thread_fn+0x159/0x2a0 ? smpboot_create_threads+0x80/0x80 kthread+0xef/0x110 ? wait_for_completion+0xf0/0x120 ? schedule_tail+0x35/0xf0 ret_from_fork+0x22/0x50 ? __init_kthread_worker+0x70/0x70 ---[ end trace eb12ae47d2382d8f ]--- notify_down_prepare: attempt to take down CPU 0 failed This bug can be reproduced by below config w/ nohz_full= all cpus: CONFIG_BOOTPARAM_HOTPLUG_CPU0=y CONFIG_DEBUG_HOTPLUG_CPU0=y CONFIG_NO_HZ_FULL=y As Thomas pointed out: | If a down prepare callback fails, then DOWN_FAILED is invoked for all | callbacks which have successfully executed DOWN_PREPARE. | | But, workqueue has actually two notifiers. One which handles | UP/DOWN_FAILED/ONLINE and one which handles DOWN_PREPARE. | | Now look at the priorities of those callbacks: | | CPU_PRI_WORKQUEUE_UP = 5 | CPU_PRI_WORKQUEUE_DOWN = -5 | | So the call order on DOWN_PREPARE is: | | CB 1 | CB ... | CB workqueue_up() -> Ignores DOWN_PREPARE | CB ... | CB X ---> Fails | | So we call up to CB X with DOWN_FAILED | | CB 1 | CB ... | CB workqueue_up() -> Handles DOWN_FAILED | CB ... | CB X-1 | | So the problem is that the workqueue stuff handles DOWN_FAILED in the up | callback, while it should do it in the down callback. Which is not a good idea | either because it wants to be called early on rollback... | | Brilliant stuff, isn't it? The hotplug rework will solve this problem because | the callbacks become symetric, but for the existing mess, we need some | workaround in the workqueue code. The boot CPU handles housekeeping duty(unbound timers, workqueues, timekeeping, ...) on behalf of full dynticks CPUs. It must remain online when nohz full is enabled. There is a priority set to every notifier_blocks: workqueue_cpu_up > tick_nohz_cpu_down > workqueue_cpu_down So tick_nohz_cpu_down callback failed when down prepare cpu 0, and notifier_blocks behind tick_nohz_cpu_down will not be called any more, which leads to workers are actually not unbound. Then hotplug state machine will fallback to undo and online cpu 0 again. Workers will be rebound unconditionally even if they are not unbound and trigger the warning in this progress. This patch fix it by catching !DISASSOCIATED to avoid rebind bound workers. Cc: Tejun Heo <tj@kernel.org> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Frédéric Weisbecker <fweisbec@gmail.com> Cc: stable@vger.kernel.org Suggested-by: Lai Jiangshan <jiangshanlai@gmail.com> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
2016-05-11 09:55:18 +00:00
/*
* XXX: CPU hotplug notifiers are weird and can call DOWN_FAILED
* w/o preceding DOWN_PREPARE. Work around it. CPU hotplug is
* being reworked and this can go away in time.
*/
if (!(pool->flags & POOL_DISASSOCIATED)) {
spin_unlock_irq(&pool->lock);
return;
}
pool->flags &= ~POOL_DISASSOCIATED;
for_each_pool_worker(worker, pool) {
workqueue: directly restore CPU affinity of workers from CPU_ONLINE Rebinding workers of a per-cpu pool after a CPU comes online involves a lot of back-and-forth mostly because only the task itself could adjust CPU affinity if PF_THREAD_BOUND was set. As CPU_ONLINE itself couldn't adjust affinity, it had to somehow coerce the workers themselves to perform set_cpus_allowed_ptr(). Due to the various states a worker can be in, this led to three different paths a worker may be rebound. worker->rebind_work is queued to busy workers. Idle ones are signaled by unlinking worker->entry and call idle_worker_rebind(). The manager isn't covered by either and implements its own mechanism. PF_THREAD_BOUND has been relaced with PF_NO_SETAFFINITY and CPU_ONLINE itself now can manipulate CPU affinity of workers. This patch replaces the existing rebind mechanism with direct one where CPU_ONLINE iterates over all workers using for_each_pool_worker(), restores CPU affinity, and clears WORKER_UNBOUND. There are a couple subtleties. All bound idle workers should have their runqueues set to that of the bound CPU; however, if the target task isn't running, set_cpus_allowed_ptr() just updates the cpus_allowed mask deferring the actual migration to when the task wakes up. This is worked around by waking up idle workers after restoring CPU affinity before any workers can become bound. Another subtlety is stems from matching @pool->nr_running with the number of running unbound workers. While DISASSOCIATED, all workers are unbound and nr_running is zero. As workers become bound again, nr_running needs to be adjusted accordingly; however, there is no good way to tell whether a given worker is running without poking into scheduler internals. Instead of clearing UNBOUND directly, rebind_workers() replaces UNBOUND with another new NOT_RUNNING flag - REBOUND, which will later be cleared by the workers themselves while preparing for the next round of work item execution. The only change needed for the workers is clearing REBOUND along with PREP. * This patch leaves for_each_busy_worker() without any user. Removed. * idle_worker_rebind(), busy_worker_rebind_fn(), worker->rebind_work and rebind logic in manager_workers() removed. * worker_thread() now looks at WORKER_DIE instead of testing whether @worker->entry is empty to determine whether it needs to do something special as dying is the only special thing now. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 20:45:21 +00:00
unsigned int worker_flags = worker->flags;
/*
workqueue: directly restore CPU affinity of workers from CPU_ONLINE Rebinding workers of a per-cpu pool after a CPU comes online involves a lot of back-and-forth mostly because only the task itself could adjust CPU affinity if PF_THREAD_BOUND was set. As CPU_ONLINE itself couldn't adjust affinity, it had to somehow coerce the workers themselves to perform set_cpus_allowed_ptr(). Due to the various states a worker can be in, this led to three different paths a worker may be rebound. worker->rebind_work is queued to busy workers. Idle ones are signaled by unlinking worker->entry and call idle_worker_rebind(). The manager isn't covered by either and implements its own mechanism. PF_THREAD_BOUND has been relaced with PF_NO_SETAFFINITY and CPU_ONLINE itself now can manipulate CPU affinity of workers. This patch replaces the existing rebind mechanism with direct one where CPU_ONLINE iterates over all workers using for_each_pool_worker(), restores CPU affinity, and clears WORKER_UNBOUND. There are a couple subtleties. All bound idle workers should have their runqueues set to that of the bound CPU; however, if the target task isn't running, set_cpus_allowed_ptr() just updates the cpus_allowed mask deferring the actual migration to when the task wakes up. This is worked around by waking up idle workers after restoring CPU affinity before any workers can become bound. Another subtlety is stems from matching @pool->nr_running with the number of running unbound workers. While DISASSOCIATED, all workers are unbound and nr_running is zero. As workers become bound again, nr_running needs to be adjusted accordingly; however, there is no good way to tell whether a given worker is running without poking into scheduler internals. Instead of clearing UNBOUND directly, rebind_workers() replaces UNBOUND with another new NOT_RUNNING flag - REBOUND, which will later be cleared by the workers themselves while preparing for the next round of work item execution. The only change needed for the workers is clearing REBOUND along with PREP. * This patch leaves for_each_busy_worker() without any user. Removed. * idle_worker_rebind(), busy_worker_rebind_fn(), worker->rebind_work and rebind logic in manager_workers() removed. * worker_thread() now looks at WORKER_DIE instead of testing whether @worker->entry is empty to determine whether it needs to do something special as dying is the only special thing now. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 20:45:21 +00:00
* A bound idle worker should actually be on the runqueue
* of the associated CPU for local wake-ups targeting it to
* work. Kick all idle workers so that they migrate to the
* associated CPU. Doing this in the same loop as
* replacing UNBOUND with REBOUND is safe as no worker will
* be bound before @pool->lock is released.
*/
workqueue: directly restore CPU affinity of workers from CPU_ONLINE Rebinding workers of a per-cpu pool after a CPU comes online involves a lot of back-and-forth mostly because only the task itself could adjust CPU affinity if PF_THREAD_BOUND was set. As CPU_ONLINE itself couldn't adjust affinity, it had to somehow coerce the workers themselves to perform set_cpus_allowed_ptr(). Due to the various states a worker can be in, this led to three different paths a worker may be rebound. worker->rebind_work is queued to busy workers. Idle ones are signaled by unlinking worker->entry and call idle_worker_rebind(). The manager isn't covered by either and implements its own mechanism. PF_THREAD_BOUND has been relaced with PF_NO_SETAFFINITY and CPU_ONLINE itself now can manipulate CPU affinity of workers. This patch replaces the existing rebind mechanism with direct one where CPU_ONLINE iterates over all workers using for_each_pool_worker(), restores CPU affinity, and clears WORKER_UNBOUND. There are a couple subtleties. All bound idle workers should have their runqueues set to that of the bound CPU; however, if the target task isn't running, set_cpus_allowed_ptr() just updates the cpus_allowed mask deferring the actual migration to when the task wakes up. This is worked around by waking up idle workers after restoring CPU affinity before any workers can become bound. Another subtlety is stems from matching @pool->nr_running with the number of running unbound workers. While DISASSOCIATED, all workers are unbound and nr_running is zero. As workers become bound again, nr_running needs to be adjusted accordingly; however, there is no good way to tell whether a given worker is running without poking into scheduler internals. Instead of clearing UNBOUND directly, rebind_workers() replaces UNBOUND with another new NOT_RUNNING flag - REBOUND, which will later be cleared by the workers themselves while preparing for the next round of work item execution. The only change needed for the workers is clearing REBOUND along with PREP. * This patch leaves for_each_busy_worker() without any user. Removed. * idle_worker_rebind(), busy_worker_rebind_fn(), worker->rebind_work and rebind logic in manager_workers() removed. * worker_thread() now looks at WORKER_DIE instead of testing whether @worker->entry is empty to determine whether it needs to do something special as dying is the only special thing now. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 20:45:21 +00:00
if (worker_flags & WORKER_IDLE)
wake_up_process(worker->task);
workqueue: directly restore CPU affinity of workers from CPU_ONLINE Rebinding workers of a per-cpu pool after a CPU comes online involves a lot of back-and-forth mostly because only the task itself could adjust CPU affinity if PF_THREAD_BOUND was set. As CPU_ONLINE itself couldn't adjust affinity, it had to somehow coerce the workers themselves to perform set_cpus_allowed_ptr(). Due to the various states a worker can be in, this led to three different paths a worker may be rebound. worker->rebind_work is queued to busy workers. Idle ones are signaled by unlinking worker->entry and call idle_worker_rebind(). The manager isn't covered by either and implements its own mechanism. PF_THREAD_BOUND has been relaced with PF_NO_SETAFFINITY and CPU_ONLINE itself now can manipulate CPU affinity of workers. This patch replaces the existing rebind mechanism with direct one where CPU_ONLINE iterates over all workers using for_each_pool_worker(), restores CPU affinity, and clears WORKER_UNBOUND. There are a couple subtleties. All bound idle workers should have their runqueues set to that of the bound CPU; however, if the target task isn't running, set_cpus_allowed_ptr() just updates the cpus_allowed mask deferring the actual migration to when the task wakes up. This is worked around by waking up idle workers after restoring CPU affinity before any workers can become bound. Another subtlety is stems from matching @pool->nr_running with the number of running unbound workers. While DISASSOCIATED, all workers are unbound and nr_running is zero. As workers become bound again, nr_running needs to be adjusted accordingly; however, there is no good way to tell whether a given worker is running without poking into scheduler internals. Instead of clearing UNBOUND directly, rebind_workers() replaces UNBOUND with another new NOT_RUNNING flag - REBOUND, which will later be cleared by the workers themselves while preparing for the next round of work item execution. The only change needed for the workers is clearing REBOUND along with PREP. * This patch leaves for_each_busy_worker() without any user. Removed. * idle_worker_rebind(), busy_worker_rebind_fn(), worker->rebind_work and rebind logic in manager_workers() removed. * worker_thread() now looks at WORKER_DIE instead of testing whether @worker->entry is empty to determine whether it needs to do something special as dying is the only special thing now. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 20:45:21 +00:00
/*
* We want to clear UNBOUND but can't directly call
* worker_clr_flags() or adjust nr_running. Atomically
* replace UNBOUND with another NOT_RUNNING flag REBOUND.
* @worker will clear REBOUND using worker_clr_flags() when
* it initiates the next execution cycle thus restoring
* concurrency management. Note that when or whether
* @worker clears REBOUND doesn't affect correctness.
*
* ACCESS_ONCE() is necessary because @worker->flags may be
* tested without holding any lock in
* wq_worker_waking_up(). Without it, NOT_RUNNING test may
* fail incorrectly leading to premature concurrency
* management operations.
*/
WARN_ON_ONCE(!(worker_flags & WORKER_UNBOUND));
worker_flags |= WORKER_REBOUND;
worker_flags &= ~WORKER_UNBOUND;
ACCESS_ONCE(worker->flags) = worker_flags;
}
workqueue: directly restore CPU affinity of workers from CPU_ONLINE Rebinding workers of a per-cpu pool after a CPU comes online involves a lot of back-and-forth mostly because only the task itself could adjust CPU affinity if PF_THREAD_BOUND was set. As CPU_ONLINE itself couldn't adjust affinity, it had to somehow coerce the workers themselves to perform set_cpus_allowed_ptr(). Due to the various states a worker can be in, this led to three different paths a worker may be rebound. worker->rebind_work is queued to busy workers. Idle ones are signaled by unlinking worker->entry and call idle_worker_rebind(). The manager isn't covered by either and implements its own mechanism. PF_THREAD_BOUND has been relaced with PF_NO_SETAFFINITY and CPU_ONLINE itself now can manipulate CPU affinity of workers. This patch replaces the existing rebind mechanism with direct one where CPU_ONLINE iterates over all workers using for_each_pool_worker(), restores CPU affinity, and clears WORKER_UNBOUND. There are a couple subtleties. All bound idle workers should have their runqueues set to that of the bound CPU; however, if the target task isn't running, set_cpus_allowed_ptr() just updates the cpus_allowed mask deferring the actual migration to when the task wakes up. This is worked around by waking up idle workers after restoring CPU affinity before any workers can become bound. Another subtlety is stems from matching @pool->nr_running with the number of running unbound workers. While DISASSOCIATED, all workers are unbound and nr_running is zero. As workers become bound again, nr_running needs to be adjusted accordingly; however, there is no good way to tell whether a given worker is running without poking into scheduler internals. Instead of clearing UNBOUND directly, rebind_workers() replaces UNBOUND with another new NOT_RUNNING flag - REBOUND, which will later be cleared by the workers themselves while preparing for the next round of work item execution. The only change needed for the workers is clearing REBOUND along with PREP. * This patch leaves for_each_busy_worker() without any user. Removed. * idle_worker_rebind(), busy_worker_rebind_fn(), worker->rebind_work and rebind logic in manager_workers() removed. * worker_thread() now looks at WORKER_DIE instead of testing whether @worker->entry is empty to determine whether it needs to do something special as dying is the only special thing now. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 20:45:21 +00:00
spin_unlock_irq(&pool->lock);
}
/**
* restore_unbound_workers_cpumask - restore cpumask of unbound workers
* @pool: unbound pool of interest
* @cpu: the CPU which is coming up
*
* An unbound pool may end up with a cpumask which doesn't have any online
* CPUs. When a worker of such pool get scheduled, the scheduler resets
* its cpus_allowed. If @cpu is in @pool's cpumask which didn't have any
* online CPU before, cpus_allowed of all its workers should be restored.
*/
static void restore_unbound_workers_cpumask(struct worker_pool *pool, int cpu)
{
static cpumask_t cpumask;
struct worker *worker;
lockdep_assert_held(&pool->attach_mutex);
/* is @cpu allowed for @pool? */
if (!cpumask_test_cpu(cpu, pool->attrs->cpumask))
return;
cpumask_and(&cpumask, pool->attrs->cpumask, cpu_online_mask);
/* as we're called from CPU_ONLINE, the following shouldn't fail */
for_each_pool_worker(worker, pool)
workqueue: Fix setting affinity of unbound worker threads With commit e9d867a67fd03ccc ("sched: Allow per-cpu kernel threads to run on online && !active"), __set_cpus_allowed_ptr() expects that only strict per-cpu kernel threads can have affinity to an online CPU which is not yet active. This assumption is currently broken in the CPU_ONLINE notification handler for the workqueues where restore_unbound_workers_cpumask() calls set_cpus_allowed_ptr() when the first cpu in the unbound worker's pool->attr->cpumask comes online. Since set_cpus_allowed_ptr() is called with pool->attr->cpumask in which only one CPU is online which is not yet active, we get the following WARN_ON during an CPU online operation. ------------[ cut here ]------------ WARNING: CPU: 40 PID: 248 at kernel/sched/core.c:1166 __set_cpus_allowed_ptr+0x228/0x2e0 Modules linked in: CPU: 40 PID: 248 Comm: cpuhp/40 Not tainted 4.6.0-autotest+ #4 <..snip..> Call Trace: [c000000f273ff920] [c00000000010493c] __set_cpus_allowed_ptr+0x2cc/0x2e0 (unreliable) [c000000f273ffac0] [c0000000000ed4b0] workqueue_cpu_up_callback+0x2c0/0x470 [c000000f273ffb70] [c0000000000f5c58] notifier_call_chain+0x98/0x100 [c000000f273ffbc0] [c0000000000c5ed0] __cpu_notify+0x70/0xe0 [c000000f273ffc00] [c0000000000c6028] notify_online+0x38/0x50 [c000000f273ffc30] [c0000000000c5214] cpuhp_invoke_callback+0x84/0x250 [c000000f273ffc90] [c0000000000c562c] cpuhp_up_callbacks+0x5c/0x120 [c000000f273ffce0] [c0000000000c64d4] cpuhp_thread_fun+0x184/0x1c0 [c000000f273ffd20] [c0000000000fa050] smpboot_thread_fn+0x290/0x2a0 [c000000f273ffd80] [c0000000000f45b0] kthread+0x110/0x130 [c000000f273ffe30] [c000000000009570] ret_from_kernel_thread+0x5c/0x6c ---[ end trace 00f1456578b2a3b2 ]--- This patch fixes this by limiting the mask to the intersection of the pool affinity and online CPUs. Changelog-cribbed-from: Gautham R. Shenoy <ego@linux.vnet.ibm.com> Reported-by: Abdul Haleem <abdhalee@linux.vnet.ibm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Tejun Heo <tj@kernel.org>
2016-06-16 12:38:42 +00:00
WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, &cpumask) < 0);
}
int workqueue_prepare_cpu(unsigned int cpu)
{
struct worker_pool *pool;
for_each_cpu_worker_pool(pool, cpu) {
if (pool->nr_workers)
continue;
if (!create_worker(pool))
return -ENOMEM;
}
return 0;
}
int workqueue_online_cpu(unsigned int cpu)
{
struct worker_pool *pool;
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
struct workqueue_struct *wq;
int pi;
mutex_lock(&wq_pool_mutex);
for_each_pool(pool, pi) {
mutex_lock(&pool->attach_mutex);
if (pool->cpu == cpu)
rebind_workers(pool);
else if (pool->cpu < 0)
restore_unbound_workers_cpumask(pool, cpu);
mutex_unlock(&pool->attach_mutex);
}
/* update NUMA affinity of unbound workqueues */
list_for_each_entry(wq, &workqueues, list)
wq_update_unbound_numa(wq, cpu, true);
mutex_unlock(&wq_pool_mutex);
return 0;
}
int workqueue_offline_cpu(unsigned int cpu)
{
struct work_struct unbind_work;
struct workqueue_struct *wq;
/* unbinding per-cpu workers should happen on the local CPU */
INIT_WORK_ONSTACK(&unbind_work, wq_unbind_fn);
queue_work_on(cpu, system_highpri_wq, &unbind_work);
/* update NUMA affinity of unbound workqueues */
mutex_lock(&wq_pool_mutex);
list_for_each_entry(wq, &workqueues, list)
wq_update_unbound_numa(wq, cpu, false);
mutex_unlock(&wq_pool_mutex);
/* wait for per-cpu unbinding to finish */
flush_work(&unbind_work);
destroy_work_on_stack(&unbind_work);
return 0;
}
#ifdef CONFIG_SMP
struct work_for_cpu {
struct work_struct work;
long (*fn)(void *);
void *arg;
long ret;
};
static void work_for_cpu_fn(struct work_struct *work)
{
struct work_for_cpu *wfc = container_of(work, struct work_for_cpu, work);
wfc->ret = wfc->fn(wfc->arg);
}
/**
* work_on_cpu - run a function in thread context on a particular cpu
* @cpu: the cpu to run on
* @fn: the function to run
* @arg: the function arg
*
* It is up to the caller to ensure that the cpu doesn't go offline.
* The caller must not hold any locks which would prevent @fn from completing.
*
* Return: The value @fn returns.
*/
long work_on_cpu(int cpu, long (*fn)(void *), void *arg)
{
struct work_for_cpu wfc = { .fn = fn, .arg = arg };
INIT_WORK_ONSTACK(&wfc.work, work_for_cpu_fn);
schedule_work_on(cpu, &wfc.work);
flush_work(&wfc.work);
destroy_work_on_stack(&wfc.work);
return wfc.ret;
}
EXPORT_SYMBOL_GPL(work_on_cpu);
#endif /* CONFIG_SMP */
#ifdef CONFIG_FREEZER
/**
* freeze_workqueues_begin - begin freezing workqueues
*
* Start freezing workqueues. After this function returns, all freezable
* workqueues will queue new works to their delayed_works list instead of
* pool->worklist.
*
* CONTEXT:
* Grabs and releases wq_pool_mutex, wq->mutex and pool->lock's.
*/
void freeze_workqueues_begin(void)
{
struct workqueue_struct *wq;
struct pool_workqueue *pwq;
mutex_lock(&wq_pool_mutex);
WARN_ON_ONCE(workqueue_freezing);
workqueue_freezing = true;
list_for_each_entry(wq, &workqueues, list) {
mutex_lock(&wq->mutex);
for_each_pwq(pwq, wq)
pwq_adjust_max_active(pwq);
mutex_unlock(&wq->mutex);
}
mutex_unlock(&wq_pool_mutex);
}
/**
* freeze_workqueues_busy - are freezable workqueues still busy?
*
* Check whether freezing is complete. This function must be called
* between freeze_workqueues_begin() and thaw_workqueues().
*
* CONTEXT:
* Grabs and releases wq_pool_mutex.
*
* Return:
* %true if some freezable workqueues are still busy. %false if freezing
* is complete.
*/
bool freeze_workqueues_busy(void)
{
bool busy = false;
struct workqueue_struct *wq;
struct pool_workqueue *pwq;
mutex_lock(&wq_pool_mutex);
WARN_ON_ONCE(!workqueue_freezing);
list_for_each_entry(wq, &workqueues, list) {
if (!(wq->flags & WQ_FREEZABLE))
continue;
/*
* nr_active is monotonically decreasing. It's safe
* to peek without lock.
*/
rcu_read_lock_sched();
for_each_pwq(pwq, wq) {
WARN_ON_ONCE(pwq->nr_active < 0);
if (pwq->nr_active) {
busy = true;
rcu_read_unlock_sched();
goto out_unlock;
}
}
rcu_read_unlock_sched();
}
out_unlock:
mutex_unlock(&wq_pool_mutex);
return busy;
}
/**
* thaw_workqueues - thaw workqueues
*
* Thaw workqueues. Normal queueing is restored and all collected
* frozen works are transferred to their respective pool worklists.
*
* CONTEXT:
* Grabs and releases wq_pool_mutex, wq->mutex and pool->lock's.
*/
void thaw_workqueues(void)
{
struct workqueue_struct *wq;
struct pool_workqueue *pwq;
mutex_lock(&wq_pool_mutex);
if (!workqueue_freezing)
goto out_unlock;
workqueue_freezing = false;
/* restore max_active and repopulate worklist */
list_for_each_entry(wq, &workqueues, list) {
mutex_lock(&wq->mutex);
for_each_pwq(pwq, wq)
pwq_adjust_max_active(pwq);
mutex_unlock(&wq->mutex);
}
out_unlock:
mutex_unlock(&wq_pool_mutex);
}
#endif /* CONFIG_FREEZER */
workqueue: Allow modifying low level unbound workqueue cpumask Allow to modify the low-level unbound workqueues cpumask through sysfs. This is performed by traversing the entire workqueue list and calling apply_wqattrs_prepare() on the unbound workqueues with the new low level mask. Only after all the preparation are done, we commit them all together. Ordered workqueues are ignored from the low level unbound workqueue cpumask, it will be handled in near future. All the (default & per-node) pwqs are mandatorily controlled by the low level cpumask. If the user configured cpumask doesn't overlap with the low level cpumask, the low level cpumask will be used for the wq instead. The comment of wq_calc_node_cpumask() is updated and explicitly requires that its first argument should be the attrs of the default pwq. The default wq_unbound_cpumask is cpu_possible_mask. The workqueue subsystem doesn't know its best default value, let the system manager or the other subsystem set it when needed. Changed from V8: merge the calculating code for the attrs of the default pwq together. minor change the code&comments for saving the user configured attrs. remove unnecessary list_del(). minor update the comment of wq_calc_node_cpumask(). update the comment of workqueue_set_unbound_cpumask(); Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Original-patch-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-30 09:16:12 +00:00
static int workqueue_apply_unbound_cpumask(void)
{
LIST_HEAD(ctxs);
int ret = 0;
struct workqueue_struct *wq;
struct apply_wqattrs_ctx *ctx, *n;
lockdep_assert_held(&wq_pool_mutex);
list_for_each_entry(wq, &workqueues, list) {
if (!(wq->flags & WQ_UNBOUND))
continue;
/* creating multiple pwqs breaks ordering guarantee */
if (wq->flags & __WQ_ORDERED)
continue;
ctx = apply_wqattrs_prepare(wq, wq->unbound_attrs);
if (!ctx) {
ret = -ENOMEM;
break;
}
list_add_tail(&ctx->list, &ctxs);
}
list_for_each_entry_safe(ctx, n, &ctxs, list) {
if (!ret)
apply_wqattrs_commit(ctx);
apply_wqattrs_cleanup(ctx);
}
return ret;
}
/**
* workqueue_set_unbound_cpumask - Set the low-level unbound cpumask
* @cpumask: the cpumask to set
*
* The low-level workqueues cpumask is a global cpumask that limits
* the affinity of all unbound workqueues. This function check the @cpumask
* and apply it to all unbound workqueues and updates all pwqs of them.
*
* Retun: 0 - Success
* -EINVAL - Invalid @cpumask
* -ENOMEM - Failed to allocate memory for attrs or pwqs.
*/
int workqueue_set_unbound_cpumask(cpumask_var_t cpumask)
{
int ret = -EINVAL;
cpumask_var_t saved_cpumask;
if (!zalloc_cpumask_var(&saved_cpumask, GFP_KERNEL))
return -ENOMEM;
cpumask_and(cpumask, cpumask, cpu_possible_mask);
if (!cpumask_empty(cpumask)) {
apply_wqattrs_lock();
workqueue: Allow modifying low level unbound workqueue cpumask Allow to modify the low-level unbound workqueues cpumask through sysfs. This is performed by traversing the entire workqueue list and calling apply_wqattrs_prepare() on the unbound workqueues with the new low level mask. Only after all the preparation are done, we commit them all together. Ordered workqueues are ignored from the low level unbound workqueue cpumask, it will be handled in near future. All the (default & per-node) pwqs are mandatorily controlled by the low level cpumask. If the user configured cpumask doesn't overlap with the low level cpumask, the low level cpumask will be used for the wq instead. The comment of wq_calc_node_cpumask() is updated and explicitly requires that its first argument should be the attrs of the default pwq. The default wq_unbound_cpumask is cpu_possible_mask. The workqueue subsystem doesn't know its best default value, let the system manager or the other subsystem set it when needed. Changed from V8: merge the calculating code for the attrs of the default pwq together. minor change the code&comments for saving the user configured attrs. remove unnecessary list_del(). minor update the comment of wq_calc_node_cpumask(). update the comment of workqueue_set_unbound_cpumask(); Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Original-patch-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-30 09:16:12 +00:00
/* save the old wq_unbound_cpumask. */
cpumask_copy(saved_cpumask, wq_unbound_cpumask);
/* update wq_unbound_cpumask at first and apply it to wqs. */
cpumask_copy(wq_unbound_cpumask, cpumask);
ret = workqueue_apply_unbound_cpumask();
/* restore the wq_unbound_cpumask when failed. */
if (ret < 0)
cpumask_copy(wq_unbound_cpumask, saved_cpumask);
apply_wqattrs_unlock();
workqueue: Allow modifying low level unbound workqueue cpumask Allow to modify the low-level unbound workqueues cpumask through sysfs. This is performed by traversing the entire workqueue list and calling apply_wqattrs_prepare() on the unbound workqueues with the new low level mask. Only after all the preparation are done, we commit them all together. Ordered workqueues are ignored from the low level unbound workqueue cpumask, it will be handled in near future. All the (default & per-node) pwqs are mandatorily controlled by the low level cpumask. If the user configured cpumask doesn't overlap with the low level cpumask, the low level cpumask will be used for the wq instead. The comment of wq_calc_node_cpumask() is updated and explicitly requires that its first argument should be the attrs of the default pwq. The default wq_unbound_cpumask is cpu_possible_mask. The workqueue subsystem doesn't know its best default value, let the system manager or the other subsystem set it when needed. Changed from V8: merge the calculating code for the attrs of the default pwq together. minor change the code&comments for saving the user configured attrs. remove unnecessary list_del(). minor update the comment of wq_calc_node_cpumask(). update the comment of workqueue_set_unbound_cpumask(); Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Original-patch-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-30 09:16:12 +00:00
}
free_cpumask_var(saved_cpumask);
return ret;
}
#ifdef CONFIG_SYSFS
/*
* Workqueues with WQ_SYSFS flag set is visible to userland via
* /sys/bus/workqueue/devices/WQ_NAME. All visible workqueues have the
* following attributes.
*
* per_cpu RO bool : whether the workqueue is per-cpu or unbound
* max_active RW int : maximum number of in-flight work items
*
* Unbound workqueues have the following extra attributes.
*
* id RO int : the associated pool ID
* nice RW int : nice value of the workers
* cpumask RW mask : bitmask of allowed CPUs for the workers
*/
struct wq_device {
struct workqueue_struct *wq;
struct device dev;
};
static struct workqueue_struct *dev_to_wq(struct device *dev)
{
struct wq_device *wq_dev = container_of(dev, struct wq_device, dev);
return wq_dev->wq;
}
static ssize_t per_cpu_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
struct workqueue_struct *wq = dev_to_wq(dev);
return scnprintf(buf, PAGE_SIZE, "%d\n", (bool)!(wq->flags & WQ_UNBOUND));
}
static DEVICE_ATTR_RO(per_cpu);
static ssize_t max_active_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct workqueue_struct *wq = dev_to_wq(dev);
return scnprintf(buf, PAGE_SIZE, "%d\n", wq->saved_max_active);
}
static ssize_t max_active_store(struct device *dev,
struct device_attribute *attr, const char *buf,
size_t count)
{
struct workqueue_struct *wq = dev_to_wq(dev);
int val;
if (sscanf(buf, "%d", &val) != 1 || val <= 0)
return -EINVAL;
workqueue_set_max_active(wq, val);
return count;
}
static DEVICE_ATTR_RW(max_active);
static struct attribute *wq_sysfs_attrs[] = {
&dev_attr_per_cpu.attr,
&dev_attr_max_active.attr,
NULL,
};
ATTRIBUTE_GROUPS(wq_sysfs);
static ssize_t wq_pool_ids_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct workqueue_struct *wq = dev_to_wq(dev);
const char *delim = "";
int node, written = 0;
rcu_read_lock_sched();
for_each_node(node) {
written += scnprintf(buf + written, PAGE_SIZE - written,
"%s%d:%d", delim, node,
unbound_pwq_by_node(wq, node)->pool->id);
delim = " ";
}
written += scnprintf(buf + written, PAGE_SIZE - written, "\n");
rcu_read_unlock_sched();
return written;
}
static ssize_t wq_nice_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
struct workqueue_struct *wq = dev_to_wq(dev);
int written;
mutex_lock(&wq->mutex);
written = scnprintf(buf, PAGE_SIZE, "%d\n", wq->unbound_attrs->nice);
mutex_unlock(&wq->mutex);
return written;
}
/* prepare workqueue_attrs for sysfs store operations */
static struct workqueue_attrs *wq_sysfs_prep_attrs(struct workqueue_struct *wq)
{
struct workqueue_attrs *attrs;
lockdep_assert_held(&wq_pool_mutex);
attrs = alloc_workqueue_attrs(GFP_KERNEL);
if (!attrs)
return NULL;
copy_workqueue_attrs(attrs, wq->unbound_attrs);
return attrs;
}
static ssize_t wq_nice_store(struct device *dev, struct device_attribute *attr,
const char *buf, size_t count)
{
struct workqueue_struct *wq = dev_to_wq(dev);
struct workqueue_attrs *attrs;
int ret = -ENOMEM;
apply_wqattrs_lock();
attrs = wq_sysfs_prep_attrs(wq);
if (!attrs)
goto out_unlock;
if (sscanf(buf, "%d", &attrs->nice) == 1 &&
attrs->nice >= MIN_NICE && attrs->nice <= MAX_NICE)
ret = apply_workqueue_attrs_locked(wq, attrs);
else
ret = -EINVAL;
out_unlock:
apply_wqattrs_unlock();
free_workqueue_attrs(attrs);
return ret ?: count;
}
static ssize_t wq_cpumask_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct workqueue_struct *wq = dev_to_wq(dev);
int written;
mutex_lock(&wq->mutex);
written = scnprintf(buf, PAGE_SIZE, "%*pb\n",
cpumask_pr_args(wq->unbound_attrs->cpumask));
mutex_unlock(&wq->mutex);
return written;
}
static ssize_t wq_cpumask_store(struct device *dev,
struct device_attribute *attr,
const char *buf, size_t count)
{
struct workqueue_struct *wq = dev_to_wq(dev);
struct workqueue_attrs *attrs;
int ret = -ENOMEM;
apply_wqattrs_lock();
attrs = wq_sysfs_prep_attrs(wq);
if (!attrs)
goto out_unlock;
ret = cpumask_parse(buf, attrs->cpumask);
if (!ret)
ret = apply_workqueue_attrs_locked(wq, attrs);
out_unlock:
apply_wqattrs_unlock();
free_workqueue_attrs(attrs);
return ret ?: count;
}
static ssize_t wq_numa_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
struct workqueue_struct *wq = dev_to_wq(dev);
int written;
mutex_lock(&wq->mutex);
written = scnprintf(buf, PAGE_SIZE, "%d\n",
!wq->unbound_attrs->no_numa);
mutex_unlock(&wq->mutex);
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
return written;
workqueue: perform cpu down operations from low priority cpu_notifier() Currently, all workqueue cpu hotplug operations run off CPU_PRI_WORKQUEUE which is higher than normal notifiers. This is to ensure that workqueue is up and running while bringing up a CPU before other notifiers try to use workqueue on the CPU. Per-cpu workqueues are supposed to remain working and bound to the CPU for normal CPU_DOWN_PREPARE notifiers. This holds mostly true even with workqueue offlining running with higher priority because workqueue CPU_DOWN_PREPARE only creates a bound trustee thread which runs the per-cpu workqueue without concurrency management without explicitly detaching the existing workers. However, if the trustee needs to create new workers, it creates unbound workers which may wander off to other CPUs while CPU_DOWN_PREPARE notifiers are in progress. Furthermore, if the CPU down is cancelled, the per-CPU workqueue may end up with workers which aren't bound to the CPU. While reliably reproducible with a convoluted artificial test-case involving scheduling and flushing CPU burning work items from CPU down notifiers, this isn't very likely to happen in the wild, and, even when it happens, the effects are likely to be hidden by the following successful CPU down. Fix it by using different priorities for up and down notifiers - high priority for up operations and low priority for down operations. Workqueue cpu hotplug operations will soon go through further cleanup. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: stable@vger.kernel.org Acked-by: "Rafael J. Wysocki" <rjw@sisk.pl>
2012-07-17 19:39:26 +00:00
}
static ssize_t wq_numa_store(struct device *dev, struct device_attribute *attr,
const char *buf, size_t count)
workqueue: perform cpu down operations from low priority cpu_notifier() Currently, all workqueue cpu hotplug operations run off CPU_PRI_WORKQUEUE which is higher than normal notifiers. This is to ensure that workqueue is up and running while bringing up a CPU before other notifiers try to use workqueue on the CPU. Per-cpu workqueues are supposed to remain working and bound to the CPU for normal CPU_DOWN_PREPARE notifiers. This holds mostly true even with workqueue offlining running with higher priority because workqueue CPU_DOWN_PREPARE only creates a bound trustee thread which runs the per-cpu workqueue without concurrency management without explicitly detaching the existing workers. However, if the trustee needs to create new workers, it creates unbound workers which may wander off to other CPUs while CPU_DOWN_PREPARE notifiers are in progress. Furthermore, if the CPU down is cancelled, the per-CPU workqueue may end up with workers which aren't bound to the CPU. While reliably reproducible with a convoluted artificial test-case involving scheduling and flushing CPU burning work items from CPU down notifiers, this isn't very likely to happen in the wild, and, even when it happens, the effects are likely to be hidden by the following successful CPU down. Fix it by using different priorities for up and down notifiers - high priority for up operations and low priority for down operations. Workqueue cpu hotplug operations will soon go through further cleanup. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: stable@vger.kernel.org Acked-by: "Rafael J. Wysocki" <rjw@sisk.pl>
2012-07-17 19:39:26 +00:00
{
struct workqueue_struct *wq = dev_to_wq(dev);
struct workqueue_attrs *attrs;
int v, ret = -ENOMEM;
apply_wqattrs_lock();
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
attrs = wq_sysfs_prep_attrs(wq);
if (!attrs)
goto out_unlock;
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
ret = -EINVAL;
if (sscanf(buf, "%d", &v) == 1) {
attrs->no_numa = !v;
ret = apply_workqueue_attrs_locked(wq, attrs);
workqueue: perform cpu down operations from low priority cpu_notifier() Currently, all workqueue cpu hotplug operations run off CPU_PRI_WORKQUEUE which is higher than normal notifiers. This is to ensure that workqueue is up and running while bringing up a CPU before other notifiers try to use workqueue on the CPU. Per-cpu workqueues are supposed to remain working and bound to the CPU for normal CPU_DOWN_PREPARE notifiers. This holds mostly true even with workqueue offlining running with higher priority because workqueue CPU_DOWN_PREPARE only creates a bound trustee thread which runs the per-cpu workqueue without concurrency management without explicitly detaching the existing workers. However, if the trustee needs to create new workers, it creates unbound workers which may wander off to other CPUs while CPU_DOWN_PREPARE notifiers are in progress. Furthermore, if the CPU down is cancelled, the per-CPU workqueue may end up with workers which aren't bound to the CPU. While reliably reproducible with a convoluted artificial test-case involving scheduling and flushing CPU burning work items from CPU down notifiers, this isn't very likely to happen in the wild, and, even when it happens, the effects are likely to be hidden by the following successful CPU down. Fix it by using different priorities for up and down notifiers - high priority for up operations and low priority for down operations. Workqueue cpu hotplug operations will soon go through further cleanup. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: stable@vger.kernel.org Acked-by: "Rafael J. Wysocki" <rjw@sisk.pl>
2012-07-17 19:39:26 +00:00
}
out_unlock:
apply_wqattrs_unlock();
free_workqueue_attrs(attrs);
return ret ?: count;
workqueue: perform cpu down operations from low priority cpu_notifier() Currently, all workqueue cpu hotplug operations run off CPU_PRI_WORKQUEUE which is higher than normal notifiers. This is to ensure that workqueue is up and running while bringing up a CPU before other notifiers try to use workqueue on the CPU. Per-cpu workqueues are supposed to remain working and bound to the CPU for normal CPU_DOWN_PREPARE notifiers. This holds mostly true even with workqueue offlining running with higher priority because workqueue CPU_DOWN_PREPARE only creates a bound trustee thread which runs the per-cpu workqueue without concurrency management without explicitly detaching the existing workers. However, if the trustee needs to create new workers, it creates unbound workers which may wander off to other CPUs while CPU_DOWN_PREPARE notifiers are in progress. Furthermore, if the CPU down is cancelled, the per-CPU workqueue may end up with workers which aren't bound to the CPU. While reliably reproducible with a convoluted artificial test-case involving scheduling and flushing CPU burning work items from CPU down notifiers, this isn't very likely to happen in the wild, and, even when it happens, the effects are likely to be hidden by the following successful CPU down. Fix it by using different priorities for up and down notifiers - high priority for up operations and low priority for down operations. Workqueue cpu hotplug operations will soon go through further cleanup. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: stable@vger.kernel.org Acked-by: "Rafael J. Wysocki" <rjw@sisk.pl>
2012-07-17 19:39:26 +00:00
}
static struct device_attribute wq_sysfs_unbound_attrs[] = {
__ATTR(pool_ids, 0444, wq_pool_ids_show, NULL),
__ATTR(nice, 0644, wq_nice_show, wq_nice_store),
__ATTR(cpumask, 0644, wq_cpumask_show, wq_cpumask_store),
__ATTR(numa, 0644, wq_numa_show, wq_numa_store),
__ATTR_NULL,
};
static struct bus_type wq_subsys = {
.name = "workqueue",
.dev_groups = wq_sysfs_groups,
};
static ssize_t wq_unbound_cpumask_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
int written;
workqueue: Allow modifying low level unbound workqueue cpumask Allow to modify the low-level unbound workqueues cpumask through sysfs. This is performed by traversing the entire workqueue list and calling apply_wqattrs_prepare() on the unbound workqueues with the new low level mask. Only after all the preparation are done, we commit them all together. Ordered workqueues are ignored from the low level unbound workqueue cpumask, it will be handled in near future. All the (default & per-node) pwqs are mandatorily controlled by the low level cpumask. If the user configured cpumask doesn't overlap with the low level cpumask, the low level cpumask will be used for the wq instead. The comment of wq_calc_node_cpumask() is updated and explicitly requires that its first argument should be the attrs of the default pwq. The default wq_unbound_cpumask is cpu_possible_mask. The workqueue subsystem doesn't know its best default value, let the system manager or the other subsystem set it when needed. Changed from V8: merge the calculating code for the attrs of the default pwq together. minor change the code&comments for saving the user configured attrs. remove unnecessary list_del(). minor update the comment of wq_calc_node_cpumask(). update the comment of workqueue_set_unbound_cpumask(); Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Original-patch-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-30 09:16:12 +00:00
mutex_lock(&wq_pool_mutex);
written = scnprintf(buf, PAGE_SIZE, "%*pb\n",
cpumask_pr_args(wq_unbound_cpumask));
workqueue: Allow modifying low level unbound workqueue cpumask Allow to modify the low-level unbound workqueues cpumask through sysfs. This is performed by traversing the entire workqueue list and calling apply_wqattrs_prepare() on the unbound workqueues with the new low level mask. Only after all the preparation are done, we commit them all together. Ordered workqueues are ignored from the low level unbound workqueue cpumask, it will be handled in near future. All the (default & per-node) pwqs are mandatorily controlled by the low level cpumask. If the user configured cpumask doesn't overlap with the low level cpumask, the low level cpumask will be used for the wq instead. The comment of wq_calc_node_cpumask() is updated and explicitly requires that its first argument should be the attrs of the default pwq. The default wq_unbound_cpumask is cpu_possible_mask. The workqueue subsystem doesn't know its best default value, let the system manager or the other subsystem set it when needed. Changed from V8: merge the calculating code for the attrs of the default pwq together. minor change the code&comments for saving the user configured attrs. remove unnecessary list_del(). minor update the comment of wq_calc_node_cpumask(). update the comment of workqueue_set_unbound_cpumask(); Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Original-patch-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-30 09:16:12 +00:00
mutex_unlock(&wq_pool_mutex);
return written;
}
workqueue: Allow modifying low level unbound workqueue cpumask Allow to modify the low-level unbound workqueues cpumask through sysfs. This is performed by traversing the entire workqueue list and calling apply_wqattrs_prepare() on the unbound workqueues with the new low level mask. Only after all the preparation are done, we commit them all together. Ordered workqueues are ignored from the low level unbound workqueue cpumask, it will be handled in near future. All the (default & per-node) pwqs are mandatorily controlled by the low level cpumask. If the user configured cpumask doesn't overlap with the low level cpumask, the low level cpumask will be used for the wq instead. The comment of wq_calc_node_cpumask() is updated and explicitly requires that its first argument should be the attrs of the default pwq. The default wq_unbound_cpumask is cpu_possible_mask. The workqueue subsystem doesn't know its best default value, let the system manager or the other subsystem set it when needed. Changed from V8: merge the calculating code for the attrs of the default pwq together. minor change the code&comments for saving the user configured attrs. remove unnecessary list_del(). minor update the comment of wq_calc_node_cpumask(). update the comment of workqueue_set_unbound_cpumask(); Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Original-patch-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-30 09:16:12 +00:00
static ssize_t wq_unbound_cpumask_store(struct device *dev,
struct device_attribute *attr, const char *buf, size_t count)
{
cpumask_var_t cpumask;
int ret;
if (!zalloc_cpumask_var(&cpumask, GFP_KERNEL))
return -ENOMEM;
ret = cpumask_parse(buf, cpumask);
if (!ret)
ret = workqueue_set_unbound_cpumask(cpumask);
free_cpumask_var(cpumask);
return ret ? ret : count;
}
static struct device_attribute wq_sysfs_cpumask_attr =
workqueue: Allow modifying low level unbound workqueue cpumask Allow to modify the low-level unbound workqueues cpumask through sysfs. This is performed by traversing the entire workqueue list and calling apply_wqattrs_prepare() on the unbound workqueues with the new low level mask. Only after all the preparation are done, we commit them all together. Ordered workqueues are ignored from the low level unbound workqueue cpumask, it will be handled in near future. All the (default & per-node) pwqs are mandatorily controlled by the low level cpumask. If the user configured cpumask doesn't overlap with the low level cpumask, the low level cpumask will be used for the wq instead. The comment of wq_calc_node_cpumask() is updated and explicitly requires that its first argument should be the attrs of the default pwq. The default wq_unbound_cpumask is cpu_possible_mask. The workqueue subsystem doesn't know its best default value, let the system manager or the other subsystem set it when needed. Changed from V8: merge the calculating code for the attrs of the default pwq together. minor change the code&comments for saving the user configured attrs. remove unnecessary list_del(). minor update the comment of wq_calc_node_cpumask(). update the comment of workqueue_set_unbound_cpumask(); Cc: Christoph Lameter <cl@linux.com> Cc: Kevin Hilman <khilman@linaro.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Original-patch-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2015-04-30 09:16:12 +00:00
__ATTR(cpumask, 0644, wq_unbound_cpumask_show,
wq_unbound_cpumask_store);
static int __init wq_sysfs_init(void)
{
int err;
err = subsys_virtual_register(&wq_subsys, NULL);
if (err)
return err;
return device_create_file(wq_subsys.dev_root, &wq_sysfs_cpumask_attr);
}
core_initcall(wq_sysfs_init);
static void wq_device_release(struct device *dev)
{
struct wq_device *wq_dev = container_of(dev, struct wq_device, dev);
kfree(wq_dev);
}
/**
* workqueue_sysfs_register - make a workqueue visible in sysfs
* @wq: the workqueue to register
*
* Expose @wq in sysfs under /sys/bus/workqueue/devices.
* alloc_workqueue*() automatically calls this function if WQ_SYSFS is set
* which is the preferred method.
*
* Workqueue user should use this function directly iff it wants to apply
* workqueue_attrs before making the workqueue visible in sysfs; otherwise,
* apply_workqueue_attrs() may race against userland updating the
* attributes.
*
* Return: 0 on success, -errno on failure.
*/
int workqueue_sysfs_register(struct workqueue_struct *wq)
{
struct wq_device *wq_dev;
int ret;
/*
* Adjusting max_active or creating new pwqs by applying
* attributes breaks ordering guarantee. Disallow exposing ordered
* workqueues.
*/
if (WARN_ON(wq->flags & __WQ_ORDERED))
return -EINVAL;
wq->wq_dev = wq_dev = kzalloc(sizeof(*wq_dev), GFP_KERNEL);
if (!wq_dev)
return -ENOMEM;
wq_dev->wq = wq;
wq_dev->dev.bus = &wq_subsys;
wq_dev->dev.release = wq_device_release;
dev_set_name(&wq_dev->dev, "%s", wq->name);
/*
* unbound_attrs are created separately. Suppress uevent until
* everything is ready.
*/
dev_set_uevent_suppress(&wq_dev->dev, true);
ret = device_register(&wq_dev->dev);
if (ret) {
kfree(wq_dev);
wq->wq_dev = NULL;
return ret;
}
if (wq->flags & WQ_UNBOUND) {
struct device_attribute *attr;
for (attr = wq_sysfs_unbound_attrs; attr->attr.name; attr++) {
ret = device_create_file(&wq_dev->dev, attr);
if (ret) {
device_unregister(&wq_dev->dev);
wq->wq_dev = NULL;
return ret;
}
}
}
dev_set_uevent_suppress(&wq_dev->dev, false);
kobject_uevent(&wq_dev->dev.kobj, KOBJ_ADD);
return 0;
}
/**
* workqueue_sysfs_unregister - undo workqueue_sysfs_register()
* @wq: the workqueue to unregister
*
* If @wq is registered to sysfs by workqueue_sysfs_register(), unregister.
*/
static void workqueue_sysfs_unregister(struct workqueue_struct *wq)
{
struct wq_device *wq_dev = wq->wq_dev;
if (!wq->wq_dev)
return;
wq->wq_dev = NULL;
device_unregister(&wq_dev->dev);
}
#else /* CONFIG_SYSFS */
static void workqueue_sysfs_unregister(struct workqueue_struct *wq) { }
#endif /* CONFIG_SYSFS */
workqueue: implement lockup detector Workqueue stalls can happen from a variety of usage bugs such as missing WQ_MEM_RECLAIM flag or concurrency managed work item indefinitely staying RUNNING. These stalls can be extremely difficult to hunt down because the usual warning mechanisms can't detect workqueue stalls and the internal state is pretty opaque. To alleviate the situation, this patch implements workqueue lockup detector. It periodically monitors all worker_pools periodically and, if any pool failed to make forward progress longer than the threshold duration, triggers warning and dumps workqueue state as follows. BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 31s! Showing busy workqueues and worker pools: workqueue events: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=17/256 pending: monkey_wrench_fn, e1000_watchdog, cache_reap, vmstat_shepherd, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, cgroup_release_agent workqueue events_power_efficient: flags=0x80 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=2/256 pending: check_lifetime, neigh_periodic_work workqueue cgroup_pidlist_destroy: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/1 pending: cgroup_pidlist_destroy_work_fn ... The detection mechanism is controller through kernel parameter workqueue.watchdog_thresh and can be updated at runtime through the sysfs module parameter file. v2: Decoupled from softlockup control knobs. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Don Zickus <dzickus@redhat.com> Cc: Ulrich Obergfell <uobergfe@redhat.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Chris Mason <clm@fb.com> Cc: Andrew Morton <akpm@linux-foundation.org>
2015-12-08 16:28:04 +00:00
/*
* Workqueue watchdog.
*
* Stall may be caused by various bugs - missing WQ_MEM_RECLAIM, illegal
* flush dependency, a concurrency managed work item which stays RUNNING
* indefinitely. Workqueue stalls can be very difficult to debug as the
* usual warning mechanisms don't trigger and internal workqueue state is
* largely opaque.
*
* Workqueue watchdog monitors all worker pools periodically and dumps
* state if some pools failed to make forward progress for a while where
* forward progress is defined as the first item on ->worklist changing.
*
* This mechanism is controlled through the kernel parameter
* "workqueue.watchdog_thresh" which can be updated at runtime through the
* corresponding sysfs parameter file.
*/
#ifdef CONFIG_WQ_WATCHDOG
static void wq_watchdog_timer_fn(unsigned long data);
static unsigned long wq_watchdog_thresh = 30;
static struct timer_list wq_watchdog_timer =
TIMER_DEFERRED_INITIALIZER(wq_watchdog_timer_fn, 0, 0);
static unsigned long wq_watchdog_touched = INITIAL_JIFFIES;
static DEFINE_PER_CPU(unsigned long, wq_watchdog_touched_cpu) = INITIAL_JIFFIES;
static void wq_watchdog_reset_touched(void)
{
int cpu;
wq_watchdog_touched = jiffies;
for_each_possible_cpu(cpu)
per_cpu(wq_watchdog_touched_cpu, cpu) = jiffies;
}
static void wq_watchdog_timer_fn(unsigned long data)
{
unsigned long thresh = READ_ONCE(wq_watchdog_thresh) * HZ;
bool lockup_detected = false;
struct worker_pool *pool;
int pi;
if (!thresh)
return;
rcu_read_lock();
for_each_pool(pool, pi) {
unsigned long pool_ts, touched, ts;
if (list_empty(&pool->worklist))
continue;
/* get the latest of pool and touched timestamps */
pool_ts = READ_ONCE(pool->watchdog_ts);
touched = READ_ONCE(wq_watchdog_touched);
if (time_after(pool_ts, touched))
ts = pool_ts;
else
ts = touched;
if (pool->cpu >= 0) {
unsigned long cpu_touched =
READ_ONCE(per_cpu(wq_watchdog_touched_cpu,
pool->cpu));
if (time_after(cpu_touched, ts))
ts = cpu_touched;
}
/* did we stall? */
if (time_after(jiffies, ts + thresh)) {
lockup_detected = true;
pr_emerg("BUG: workqueue lockup - pool");
pr_cont_pool_info(pool);
pr_cont(" stuck for %us!\n",
jiffies_to_msecs(jiffies - pool_ts) / 1000);
}
}
rcu_read_unlock();
if (lockup_detected)
show_workqueue_state();
wq_watchdog_reset_touched();
mod_timer(&wq_watchdog_timer, jiffies + thresh);
}
void wq_watchdog_touch(int cpu)
{
if (cpu >= 0)
per_cpu(wq_watchdog_touched_cpu, cpu) = jiffies;
else
wq_watchdog_touched = jiffies;
}
static void wq_watchdog_set_thresh(unsigned long thresh)
{
wq_watchdog_thresh = 0;
del_timer_sync(&wq_watchdog_timer);
if (thresh) {
wq_watchdog_thresh = thresh;
wq_watchdog_reset_touched();
mod_timer(&wq_watchdog_timer, jiffies + thresh * HZ);
}
}
static int wq_watchdog_param_set_thresh(const char *val,
const struct kernel_param *kp)
{
unsigned long thresh;
int ret;
ret = kstrtoul(val, 0, &thresh);
if (ret)
return ret;
if (system_wq)
wq_watchdog_set_thresh(thresh);
else
wq_watchdog_thresh = thresh;
return 0;
}
static const struct kernel_param_ops wq_watchdog_thresh_ops = {
.set = wq_watchdog_param_set_thresh,
.get = param_get_ulong,
};
module_param_cb(watchdog_thresh, &wq_watchdog_thresh_ops, &wq_watchdog_thresh,
0644);
static void wq_watchdog_init(void)
{
wq_watchdog_set_thresh(wq_watchdog_thresh);
}
#else /* CONFIG_WQ_WATCHDOG */
static inline void wq_watchdog_init(void) { }
#endif /* CONFIG_WQ_WATCHDOG */
static void __init wq_numa_init(void)
{
cpumask_var_t *tbl;
int node, cpu;
if (num_possible_nodes() <= 1)
return;
if (wq_disable_numa) {
pr_info("workqueue: NUMA affinity support disabled\n");
return;
}
workqueue: implement NUMA affinity for unbound workqueues Currently, an unbound workqueue has single current, or first, pwq (pool_workqueue) to which all new work items are queued. This often isn't optimal on NUMA machines as workers may jump around across node boundaries and work items get assigned to workers without any regard to NUMA affinity. This patch implements NUMA affinity for unbound workqueues. Instead of mapping all entries of numa_pwq_tbl[] to the same pwq, apply_workqueue_attrs() now creates a separate pwq covering the intersecting CPUs for each NUMA node which has online CPUs in @attrs->cpumask. Nodes which don't have intersecting possible CPUs are mapped to pwqs covering whole @attrs->cpumask. As CPUs come up and go down, the pool association is changed accordingly. Changing pool association may involve allocating new pools which may fail. To avoid failing CPU_DOWN, each workqueue always keeps a default pwq which covers whole attrs->cpumask which is used as fallback if pool creation fails during a CPU hotplug operation. This ensures that all work items issued on a NUMA node is executed on the same node as long as the workqueue allows execution on the CPUs of the node. As this maps a workqueue to multiple pwqs and max_active is per-pwq, this change the behavior of max_active. The limit is now per NUMA node instead of global. While this is an actual change, max_active is already per-cpu for per-cpu workqueues and primarily used as safety mechanism rather than for active concurrency control. Concurrency is usually limited from workqueue users by the number of concurrently active work items and this change shouldn't matter much. v2: Fixed pwq freeing in apply_workqueue_attrs() error path. Spotted by Lai. v3: The previous version incorrectly made a workqueue spanning multiple nodes spread work items over all online CPUs when some of its nodes don't have any desired cpus. Reimplemented so that NUMA affinity is properly updated as CPUs go up and down. This problem was spotted by Lai Jiangshan. v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it; however, wq may be freed at any time after dfl_pwq is put making the clearing use-after-free. Clear wq->dfl_pwq before putting it. v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and @pwq_tbl after success. Fixed. Retry loop in wq_update_unbound_numa_attrs() isn't necessary as application of new attrs is excluded via CPU hotplug. Removed. Documentation on CPU affinity guarantee on CPU_DOWN added. All changes are suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 18:23:36 +00:00
wq_update_unbound_numa_attrs_buf = alloc_workqueue_attrs(GFP_KERNEL);
BUG_ON(!wq_update_unbound_numa_attrs_buf);
/*
* We want masks of possible CPUs of each node which isn't readily
* available. Build one from cpu_to_node() which should have been
* fully initialized by now.
*/
tbl = kzalloc(nr_node_ids * sizeof(tbl[0]), GFP_KERNEL);
BUG_ON(!tbl);
for_each_node(node)
workqueue: zero cpumask of wq_numa_possible_cpumask on init When hot-adding and onlining CPU, kernel panic occurs, showing following call trace. BUG: unable to handle kernel paging request at 0000000000001d08 IP: [<ffffffff8114acfd>] __alloc_pages_nodemask+0x9d/0xb10 PGD 0 Oops: 0000 [#1] SMP ... Call Trace: [<ffffffff812b8745>] ? cpumask_next_and+0x35/0x50 [<ffffffff810a3283>] ? find_busiest_group+0x113/0x8f0 [<ffffffff81193bc9>] ? deactivate_slab+0x349/0x3c0 [<ffffffff811926f1>] new_slab+0x91/0x300 [<ffffffff815de95a>] __slab_alloc+0x2bb/0x482 [<ffffffff8105bc1c>] ? copy_process.part.25+0xfc/0x14c0 [<ffffffff810a3c78>] ? load_balance+0x218/0x890 [<ffffffff8101a679>] ? sched_clock+0x9/0x10 [<ffffffff81105ba9>] ? trace_clock_local+0x9/0x10 [<ffffffff81193d1c>] kmem_cache_alloc_node+0x8c/0x200 [<ffffffff8105bc1c>] copy_process.part.25+0xfc/0x14c0 [<ffffffff81114d0d>] ? trace_buffer_unlock_commit+0x4d/0x60 [<ffffffff81085a80>] ? kthread_create_on_node+0x140/0x140 [<ffffffff8105d0ec>] do_fork+0xbc/0x360 [<ffffffff8105d3b6>] kernel_thread+0x26/0x30 [<ffffffff81086652>] kthreadd+0x2c2/0x300 [<ffffffff81086390>] ? kthread_create_on_cpu+0x60/0x60 [<ffffffff815f20ec>] ret_from_fork+0x7c/0xb0 [<ffffffff81086390>] ? kthread_create_on_cpu+0x60/0x60 In my investigation, I found the root cause is wq_numa_possible_cpumask. All entries of wq_numa_possible_cpumask is allocated by alloc_cpumask_var_node(). And these entries are used without initializing. So these entries have wrong value. When hot-adding and onlining CPU, wq_update_unbound_numa() is called. wq_update_unbound_numa() calls alloc_unbound_pwq(). And alloc_unbound_pwq() calls get_unbound_pool(). In get_unbound_pool(), worker_pool->node is set as follow: 3592 /* if cpumask is contained inside a NUMA node, we belong to that node */ 3593 if (wq_numa_enabled) { 3594 for_each_node(node) { 3595 if (cpumask_subset(pool->attrs->cpumask, 3596 wq_numa_possible_cpumask[node])) { 3597 pool->node = node; 3598 break; 3599 } 3600 } 3601 } But wq_numa_possible_cpumask[node] does not have correct cpumask. So, wrong node is selected. As a result, kernel panic occurs. By this patch, all entries of wq_numa_possible_cpumask are allocated by zalloc_cpumask_var_node to initialize them. And the panic disappeared. Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org> Cc: stable@vger.kernel.org Fixes: bce903809ab3 ("workqueue: add wq_numa_tbl_len and wq_numa_possible_cpumask[]")
2014-07-07 13:56:48 +00:00
BUG_ON(!zalloc_cpumask_var_node(&tbl[node], GFP_KERNEL,
workqueue: don't perform NUMA-aware allocations on offline nodes in wq_numa_init() wq_numa_init() builds per-node cpumasks which are later used to make unbound workqueues NUMA-aware. The cpumasks are allocated using alloc_cpumask_var_node() for all possible nodes. Unfortunately, on machines with off-line nodes, this leads to NUMA-aware allocations on existing bug offline nodes, which in turn triggers BUG in the memory allocation code. Fix it by using NUMA_NO_NODE for cpumask allocations for offline nodes. kernel BUG at include/linux/gfp.h:323! invalid opcode: 0000 [#1] SMP Modules linked in: CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.9.0+ #1 Hardware name: ProLiant BL465c G7, BIOS A19 12/10/2011 task: ffff880234608000 ti: ffff880234602000 task.ti: ffff880234602000 RIP: 0010:[<ffffffff8117495d>] [<ffffffff8117495d>] new_slab+0x2ad/0x340 RSP: 0000:ffff880234603bf8 EFLAGS: 00010246 RAX: 0000000000000000 RBX: ffff880237404b40 RCX: 00000000000000d0 RDX: 0000000000000001 RSI: 0000000000000003 RDI: 00000000002052d0 RBP: ffff880234603c28 R08: 0000000000000000 R09: 0000000000000001 R10: 0000000000000001 R11: ffffffff812e3aa8 R12: 0000000000000001 R13: ffff8802378161c0 R14: 0000000000030027 R15: 00000000000040d0 FS: 0000000000000000(0000) GS:ffff880237800000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b CR2: ffff88043fdff000 CR3: 00000000018d5000 CR4: 00000000000007f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Stack: ffff880234603c28 0000000000000001 00000000000000d0 ffff8802378161c0 ffff880237404b40 ffff880237404b40 ffff880234603d28 ffffffff815edba1 ffff880237816140 0000000000000000 ffff88023740e1c0 Call Trace: [<ffffffff815edba1>] __slab_alloc+0x330/0x4f2 [<ffffffff81174b25>] kmem_cache_alloc_node_trace+0xa5/0x200 [<ffffffff812e3aa8>] alloc_cpumask_var_node+0x28/0x90 [<ffffffff81a0bdb3>] wq_numa_init+0x10d/0x1be [<ffffffff81a0bec8>] init_workqueues+0x64/0x341 [<ffffffff810002ea>] do_one_initcall+0xea/0x1a0 [<ffffffff819f1f31>] kernel_init_freeable+0xb7/0x1ec [<ffffffff815d50de>] kernel_init+0xe/0xf0 [<ffffffff815ff89c>] ret_from_fork+0x7c/0xb0 Code: 45 84 ac 00 00 00 f0 41 80 4d 00 40 e9 f6 fe ff ff 66 0f 1f 84 00 00 00 00 00 e8 eb 4b ff ff 49 89 c5 e9 05 fe ff ff <0f> 0b 4c 8b 73 38 44 89 ff 81 cf 00 00 20 00 4c 89 f6 48 c1 ee Signed-off-by: Tejun Heo <tj@kernel.org> Reported-and-Tested-by: Lingzhu Xiang <lxiang@redhat.com>
2013-05-15 21:24:24 +00:00
node_online(node) ? node : NUMA_NO_NODE));
for_each_possible_cpu(cpu) {
node = cpu_to_node(cpu);
if (WARN_ON(node == NUMA_NO_NODE)) {
pr_warn("workqueue: NUMA node mapping not available for cpu%d, disabling NUMA support\n", cpu);
/* happens iff arch is bonkers, let's just proceed */
return;
}
cpumask_set_cpu(cpu, tbl[node]);
}
wq_numa_possible_cpumask = tbl;
wq_numa_enabled = true;
}
workqueue: make workqueue available early during boot Workqueue is currently initialized in an early init call; however, there are cases where early boot code has to be split and reordered to come after workqueue initialization or the same code path which makes use of workqueues is used both before workqueue initailization and after. The latter cases have to gate workqueue usages with keventd_up() tests, which is nasty and easy to get wrong. Workqueue usages have become widespread and it'd be a lot more convenient if it can be used very early from boot. This patch splits workqueue initialization into two steps. workqueue_init_early() which sets up the basic data structures so that workqueues can be created and work items queued, and workqueue_init() which actually brings up workqueues online and starts executing queued work items. The former step can be done very early during boot once memory allocation, cpumasks and idr are initialized. The latter right after kthreads become available. This allows work item queueing and canceling from very early boot which is what most of these use cases want. * As systemd_wq being initialized doesn't indicate that workqueue is fully online anymore, update keventd_up() to test wq_online instead. The follow-up patches will get rid of all its usages and the function itself. * Flushing doesn't make sense before workqueue is fully initialized. The flush functions trigger WARN and return immediately before fully online. * Work items are never in-flight before fully online. Canceling can always succeed by skipping the flush step. * Some code paths can no longer assume to be called with irq enabled as irq is disabled during early boot. Use irqsave/restore operations instead. v2: Watchdog init, which requires timer to be running, moved from workqueue_init_early() to workqueue_init(). Signed-off-by: Tejun Heo <tj@kernel.org> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/CA+55aFx0vPuMuxn00rBSM192n-Du5uxy+4AvKa0SBSOVJeuCGg@mail.gmail.com
2016-09-16 19:49:32 +00:00
/**
* workqueue_init_early - early init for workqueue subsystem
*
* This is the first half of two-staged workqueue subsystem initialization
* and invoked as soon as the bare basics - memory allocation, cpumasks and
* idr are up. It sets up all the data structures and system workqueues
* and allows early boot code to create workqueues and queue/cancel work
* items. Actual work item execution starts only after kthreads can be
* created and scheduled right before early initcalls.
*/
int __init workqueue_init_early(void)
{
int std_nice[NR_STD_WORKER_POOLS] = { 0, HIGHPRI_NICE_LEVEL };
int i, cpu;
WARN_ON(__alignof__(struct pool_workqueue) < __alignof__(long long));
BUG_ON(!alloc_cpumask_var(&wq_unbound_cpumask, GFP_KERNEL));
cpumask_copy(wq_unbound_cpumask, cpu_possible_mask);
pwq_cache = KMEM_CACHE(pool_workqueue, SLAB_PANIC);
wq_numa_init();
/* initialize CPU pools */
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
for_each_possible_cpu(cpu) {
struct worker_pool *pool;
i = 0;
for_each_cpu_worker_pool(pool, cpu) {
BUG_ON(init_worker_pool(pool));
pool->cpu = cpu;
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
cpumask_copy(pool->attrs->cpumask, cpumask_of(cpu));
pool->attrs->nice = std_nice[i++];
pool->node = cpu_to_node(cpu);
/* alloc pool ID */
mutex_lock(&wq_pool_mutex);
BUG_ON(worker_pool_assign_id(pool));
mutex_unlock(&wq_pool_mutex);
}
}
/* create default unbound and ordered wq attrs */
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
for (i = 0; i < NR_STD_WORKER_POOLS; i++) {
struct workqueue_attrs *attrs;
BUG_ON(!(attrs = alloc_workqueue_attrs(GFP_KERNEL)));
attrs->nice = std_nice[i];
unbound_std_wq_attrs[i] = attrs;
/*
* An ordered wq should have only one pwq as ordering is
* guaranteed by max_active which is enforced by pwqs.
* Turn off NUMA so that dfl_pwq is used for all nodes.
*/
BUG_ON(!(attrs = alloc_workqueue_attrs(GFP_KERNEL)));
attrs->nice = std_nice[i];
attrs->no_numa = true;
ordered_wq_attrs[i] = attrs;
workqueue: implement attribute-based unbound worker_pool management This patch makes unbound worker_pools reference counted and dynamically created and destroyed as workqueues needing them come and go. All unbound worker_pools are hashed on unbound_pool_hash which is keyed by the content of worker_pool->attrs. When an unbound workqueue is allocated, get_unbound_pool() is called with the attributes of the workqueue. If there already is a matching worker_pool, the reference count is bumped and the pool is returned. If not, a new worker_pool with matching attributes is created and returned. When an unbound workqueue is destroyed, put_unbound_pool() is called which decrements the reference count of the associated worker_pool. If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU safe way. Note that the standard unbound worker_pools - normal and highpri ones with no specific cpumask affinity - are no longer created explicitly during init_workqueues(). init_workqueues() only initializes workqueue_attrs to be used for standard unbound pools - unbound_std_wq_attrs[]. The pools are spawned on demand as workqueues are created. v2: - Comment added to init_worker_pool() explaining that @pool should be in a condition which can be passed to put_unbound_pool() even on failure. - pool->refcnt reaching zero and the pool being removed from unbound_pool_hash should be dynamic. pool->refcnt is converted to int from atomic_t and now manipulated inside workqueue_lock. - Removed an incorrect sanity check on nr_idle in put_unbound_pool() which may trigger spuriously. All changes were suggested by Lai Jiangshan. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-12 18:30:03 +00:00
}
system_wq = alloc_workqueue("events", 0, 0);
system_highpri_wq = alloc_workqueue("events_highpri", WQ_HIGHPRI, 0);
system_long_wq = alloc_workqueue("events_long", 0, 0);
system_unbound_wq = alloc_workqueue("events_unbound", WQ_UNBOUND,
WQ_UNBOUND_MAX_ACTIVE);
system_freezable_wq = alloc_workqueue("events_freezable",
WQ_FREEZABLE, 0);
system_power_efficient_wq = alloc_workqueue("events_power_efficient",
WQ_POWER_EFFICIENT, 0);
system_freezable_power_efficient_wq = alloc_workqueue("events_freezable_power_efficient",
WQ_FREEZABLE | WQ_POWER_EFFICIENT,
0);
BUG_ON(!system_wq || !system_highpri_wq || !system_long_wq ||
!system_unbound_wq || !system_freezable_wq ||
!system_power_efficient_wq ||
!system_freezable_power_efficient_wq);
workqueue: implement lockup detector Workqueue stalls can happen from a variety of usage bugs such as missing WQ_MEM_RECLAIM flag or concurrency managed work item indefinitely staying RUNNING. These stalls can be extremely difficult to hunt down because the usual warning mechanisms can't detect workqueue stalls and the internal state is pretty opaque. To alleviate the situation, this patch implements workqueue lockup detector. It periodically monitors all worker_pools periodically and, if any pool failed to make forward progress longer than the threshold duration, triggers warning and dumps workqueue state as follows. BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 31s! Showing busy workqueues and worker pools: workqueue events: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=17/256 pending: monkey_wrench_fn, e1000_watchdog, cache_reap, vmstat_shepherd, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, cgroup_release_agent workqueue events_power_efficient: flags=0x80 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=2/256 pending: check_lifetime, neigh_periodic_work workqueue cgroup_pidlist_destroy: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/1 pending: cgroup_pidlist_destroy_work_fn ... The detection mechanism is controller through kernel parameter workqueue.watchdog_thresh and can be updated at runtime through the sysfs module parameter file. v2: Decoupled from softlockup control knobs. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Don Zickus <dzickus@redhat.com> Cc: Ulrich Obergfell <uobergfe@redhat.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Chris Mason <clm@fb.com> Cc: Andrew Morton <akpm@linux-foundation.org>
2015-12-08 16:28:04 +00:00
workqueue: make workqueue available early during boot Workqueue is currently initialized in an early init call; however, there are cases where early boot code has to be split and reordered to come after workqueue initialization or the same code path which makes use of workqueues is used both before workqueue initailization and after. The latter cases have to gate workqueue usages with keventd_up() tests, which is nasty and easy to get wrong. Workqueue usages have become widespread and it'd be a lot more convenient if it can be used very early from boot. This patch splits workqueue initialization into two steps. workqueue_init_early() which sets up the basic data structures so that workqueues can be created and work items queued, and workqueue_init() which actually brings up workqueues online and starts executing queued work items. The former step can be done very early during boot once memory allocation, cpumasks and idr are initialized. The latter right after kthreads become available. This allows work item queueing and canceling from very early boot which is what most of these use cases want. * As systemd_wq being initialized doesn't indicate that workqueue is fully online anymore, update keventd_up() to test wq_online instead. The follow-up patches will get rid of all its usages and the function itself. * Flushing doesn't make sense before workqueue is fully initialized. The flush functions trigger WARN and return immediately before fully online. * Work items are never in-flight before fully online. Canceling can always succeed by skipping the flush step. * Some code paths can no longer assume to be called with irq enabled as irq is disabled during early boot. Use irqsave/restore operations instead. v2: Watchdog init, which requires timer to be running, moved from workqueue_init_early() to workqueue_init(). Signed-off-by: Tejun Heo <tj@kernel.org> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/CA+55aFx0vPuMuxn00rBSM192n-Du5uxy+4AvKa0SBSOVJeuCGg@mail.gmail.com
2016-09-16 19:49:32 +00:00
return 0;
}
/**
* workqueue_init - bring workqueue subsystem fully online
*
* This is the latter half of two-staged workqueue subsystem initialization
* and invoked as soon as kthreads can be created and scheduled.
* Workqueues have been created and work items queued on them, but there
* are no kworkers executing the work items yet. Populate the worker pools
* with the initial workers and enable future kworker creations.
*/
int __init workqueue_init(void)
{
struct worker_pool *pool;
int cpu, bkt;
/* create the initial workers */
for_each_online_cpu(cpu) {
for_each_cpu_worker_pool(pool, cpu) {
pool->flags &= ~POOL_DISASSOCIATED;
BUG_ON(!create_worker(pool));
}
}
hash_for_each(unbound_pool_hash, bkt, pool, hash_node)
BUG_ON(!create_worker(pool));
wq_online = true;
workqueue: implement lockup detector Workqueue stalls can happen from a variety of usage bugs such as missing WQ_MEM_RECLAIM flag or concurrency managed work item indefinitely staying RUNNING. These stalls can be extremely difficult to hunt down because the usual warning mechanisms can't detect workqueue stalls and the internal state is pretty opaque. To alleviate the situation, this patch implements workqueue lockup detector. It periodically monitors all worker_pools periodically and, if any pool failed to make forward progress longer than the threshold duration, triggers warning and dumps workqueue state as follows. BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 31s! Showing busy workqueues and worker pools: workqueue events: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=17/256 pending: monkey_wrench_fn, e1000_watchdog, cache_reap, vmstat_shepherd, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, cgroup_release_agent workqueue events_power_efficient: flags=0x80 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=2/256 pending: check_lifetime, neigh_periodic_work workqueue cgroup_pidlist_destroy: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/1 pending: cgroup_pidlist_destroy_work_fn ... The detection mechanism is controller through kernel parameter workqueue.watchdog_thresh and can be updated at runtime through the sysfs module parameter file. v2: Decoupled from softlockup control knobs. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Don Zickus <dzickus@redhat.com> Cc: Ulrich Obergfell <uobergfe@redhat.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Chris Mason <clm@fb.com> Cc: Andrew Morton <akpm@linux-foundation.org>
2015-12-08 16:28:04 +00:00
wq_watchdog_init();
return 0;
}