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a4683487f9
In response to an async related regression James noted: "My theory is that this is an init problem: The assumption in a lot of our code is that async_synchronize_full() waits for everything ... even the domain specific async schedules, which isn't true." ...so make this assumption true. Each domain, including the default one, registers itself on a global domain list when work is scheduled. Once all entries complete it exits that list. Waiting for the list to be empty syncs all in-flight work across all domains. Domains can opt-out of global syncing if they are declared as exclusive ASYNC_DOMAIN_EXCLUSIVE(). All stack-based domains have been declared exclusive since the domain may go out of scope as soon as the last work item completes. Statically declared domains are mostly ok, but async_unregister_domain() is there to close any theoretical races with pending async_synchronize_full waiters at module removal time. Signed-off-by: Dan Williams <dan.j.williams@intel.com> Acked-by: Arjan van de Ven <arjan@linux.intel.com> Reported-by: Meelis Roos <mroos@linux.ee> Reported-by: Eldad Zack <eldadzack@gmail.com> Tested-by: Eldad Zack <eldad@fogrefinery.com> Signed-off-by: James Bottomley <JBottomley@Parallels.com>
340 lines
10 KiB
C
340 lines
10 KiB
C
/*
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* async.c: Asynchronous function calls for boot performance
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*
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* (C) Copyright 2009 Intel Corporation
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* Author: Arjan van de Ven <arjan@linux.intel.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; version 2
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* of the License.
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*/
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/*
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Goals and Theory of Operation
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The primary goal of this feature is to reduce the kernel boot time,
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by doing various independent hardware delays and discovery operations
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decoupled and not strictly serialized.
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More specifically, the asynchronous function call concept allows
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certain operations (primarily during system boot) to happen
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asynchronously, out of order, while these operations still
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have their externally visible parts happen sequentially and in-order.
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(not unlike how out-of-order CPUs retire their instructions in order)
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Key to the asynchronous function call implementation is the concept of
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a "sequence cookie" (which, although it has an abstracted type, can be
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thought of as a monotonically incrementing number).
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The async core will assign each scheduled event such a sequence cookie and
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pass this to the called functions.
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The asynchronously called function should before doing a globally visible
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operation, such as registering device numbers, call the
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async_synchronize_cookie() function and pass in its own cookie. The
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async_synchronize_cookie() function will make sure that all asynchronous
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operations that were scheduled prior to the operation corresponding with the
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cookie have completed.
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Subsystem/driver initialization code that scheduled asynchronous probe
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functions, but which shares global resources with other drivers/subsystems
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that do not use the asynchronous call feature, need to do a full
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synchronization with the async_synchronize_full() function, before returning
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from their init function. This is to maintain strict ordering between the
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asynchronous and synchronous parts of the kernel.
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*/
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#include <linux/async.h>
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#include <linux/atomic.h>
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#include <linux/ktime.h>
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#include <linux/export.h>
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#include <linux/wait.h>
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#include <linux/sched.h>
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#include <linux/slab.h>
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#include <linux/workqueue.h>
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static async_cookie_t next_cookie = 1;
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#define MAX_WORK 32768
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static LIST_HEAD(async_pending);
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static ASYNC_DOMAIN(async_running);
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static LIST_HEAD(async_domains);
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static DEFINE_SPINLOCK(async_lock);
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static DEFINE_MUTEX(async_register_mutex);
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struct async_entry {
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struct list_head list;
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struct work_struct work;
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async_cookie_t cookie;
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async_func_ptr *func;
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void *data;
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struct async_domain *running;
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};
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static DECLARE_WAIT_QUEUE_HEAD(async_done);
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static atomic_t entry_count;
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/*
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* MUST be called with the lock held!
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*/
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static async_cookie_t __lowest_in_progress(struct async_domain *running)
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{
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struct async_entry *entry;
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if (!list_empty(&running->domain)) {
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entry = list_first_entry(&running->domain, typeof(*entry), list);
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return entry->cookie;
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}
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list_for_each_entry(entry, &async_pending, list)
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if (entry->running == running)
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return entry->cookie;
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return next_cookie; /* "infinity" value */
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}
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static async_cookie_t lowest_in_progress(struct async_domain *running)
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{
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unsigned long flags;
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async_cookie_t ret;
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spin_lock_irqsave(&async_lock, flags);
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ret = __lowest_in_progress(running);
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spin_unlock_irqrestore(&async_lock, flags);
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return ret;
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}
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/*
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* pick the first pending entry and run it
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*/
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static void async_run_entry_fn(struct work_struct *work)
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{
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struct async_entry *entry =
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container_of(work, struct async_entry, work);
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unsigned long flags;
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ktime_t uninitialized_var(calltime), delta, rettime;
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struct async_domain *running = entry->running;
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/* 1) move self to the running queue */
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spin_lock_irqsave(&async_lock, flags);
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list_move_tail(&entry->list, &running->domain);
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spin_unlock_irqrestore(&async_lock, flags);
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/* 2) run (and print duration) */
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if (initcall_debug && system_state == SYSTEM_BOOTING) {
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printk(KERN_DEBUG "calling %lli_%pF @ %i\n",
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(long long)entry->cookie,
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entry->func, task_pid_nr(current));
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calltime = ktime_get();
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}
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entry->func(entry->data, entry->cookie);
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if (initcall_debug && system_state == SYSTEM_BOOTING) {
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rettime = ktime_get();
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delta = ktime_sub(rettime, calltime);
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printk(KERN_DEBUG "initcall %lli_%pF returned 0 after %lld usecs\n",
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(long long)entry->cookie,
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entry->func,
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(long long)ktime_to_ns(delta) >> 10);
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}
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/* 3) remove self from the running queue */
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spin_lock_irqsave(&async_lock, flags);
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list_del(&entry->list);
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if (running->registered && --running->count == 0)
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list_del_init(&running->node);
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/* 4) free the entry */
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kfree(entry);
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atomic_dec(&entry_count);
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spin_unlock_irqrestore(&async_lock, flags);
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/* 5) wake up any waiters */
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wake_up(&async_done);
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}
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static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct async_domain *running)
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{
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struct async_entry *entry;
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unsigned long flags;
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async_cookie_t newcookie;
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/* allow irq-off callers */
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entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
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/*
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* If we're out of memory or if there's too much work
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* pending already, we execute synchronously.
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*/
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if (!entry || atomic_read(&entry_count) > MAX_WORK) {
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kfree(entry);
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spin_lock_irqsave(&async_lock, flags);
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newcookie = next_cookie++;
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spin_unlock_irqrestore(&async_lock, flags);
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/* low on memory.. run synchronously */
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ptr(data, newcookie);
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return newcookie;
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}
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INIT_WORK(&entry->work, async_run_entry_fn);
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entry->func = ptr;
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entry->data = data;
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entry->running = running;
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spin_lock_irqsave(&async_lock, flags);
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newcookie = entry->cookie = next_cookie++;
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list_add_tail(&entry->list, &async_pending);
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if (running->registered && running->count++ == 0)
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list_add_tail(&running->node, &async_domains);
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atomic_inc(&entry_count);
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spin_unlock_irqrestore(&async_lock, flags);
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/* schedule for execution */
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queue_work(system_unbound_wq, &entry->work);
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return newcookie;
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}
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/**
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* async_schedule - schedule a function for asynchronous execution
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* @ptr: function to execute asynchronously
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* @data: data pointer to pass to the function
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*
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* Returns an async_cookie_t that may be used for checkpointing later.
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* Note: This function may be called from atomic or non-atomic contexts.
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*/
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async_cookie_t async_schedule(async_func_ptr *ptr, void *data)
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{
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return __async_schedule(ptr, data, &async_running);
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}
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EXPORT_SYMBOL_GPL(async_schedule);
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/**
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* async_schedule_domain - schedule a function for asynchronous execution within a certain domain
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* @ptr: function to execute asynchronously
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* @data: data pointer to pass to the function
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* @running: running list for the domain
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*
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* Returns an async_cookie_t that may be used for checkpointing later.
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* @running may be used in the async_synchronize_*_domain() functions
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* to wait within a certain synchronization domain rather than globally.
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* A synchronization domain is specified via the running queue @running to use.
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* Note: This function may be called from atomic or non-atomic contexts.
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*/
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async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data,
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struct async_domain *running)
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{
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return __async_schedule(ptr, data, running);
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}
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EXPORT_SYMBOL_GPL(async_schedule_domain);
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/**
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* async_synchronize_full - synchronize all asynchronous function calls
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*
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* This function waits until all asynchronous function calls have been done.
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*/
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void async_synchronize_full(void)
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{
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mutex_lock(&async_register_mutex);
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do {
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struct async_domain *domain = NULL;
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spin_lock_irq(&async_lock);
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if (!list_empty(&async_domains))
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domain = list_first_entry(&async_domains, typeof(*domain), node);
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spin_unlock_irq(&async_lock);
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async_synchronize_cookie_domain(next_cookie, domain);
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} while (!list_empty(&async_domains));
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mutex_unlock(&async_register_mutex);
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}
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EXPORT_SYMBOL_GPL(async_synchronize_full);
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/**
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* async_unregister_domain - ensure no more anonymous waiters on this domain
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* @domain: idle domain to flush out of any async_synchronize_full instances
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*
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* async_synchronize_{cookie|full}_domain() are not flushed since callers
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* of these routines should know the lifetime of @domain
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*
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* Prefer ASYNC_DOMAIN_EXCLUSIVE() declarations over flushing
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*/
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void async_unregister_domain(struct async_domain *domain)
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{
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mutex_lock(&async_register_mutex);
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spin_lock_irq(&async_lock);
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WARN_ON(!domain->registered || !list_empty(&domain->node) ||
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!list_empty(&domain->domain));
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domain->registered = 0;
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spin_unlock_irq(&async_lock);
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mutex_unlock(&async_register_mutex);
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}
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EXPORT_SYMBOL_GPL(async_unregister_domain);
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/**
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* async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
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* @domain: running list to synchronize on
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*
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* This function waits until all asynchronous function calls for the
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* synchronization domain specified by the running list @domain have been done.
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*/
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void async_synchronize_full_domain(struct async_domain *domain)
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{
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async_synchronize_cookie_domain(next_cookie, domain);
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}
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EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
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/**
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* async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
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* @cookie: async_cookie_t to use as checkpoint
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* @running: running list to synchronize on
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*
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* This function waits until all asynchronous function calls for the
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* synchronization domain specified by running list @running submitted
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* prior to @cookie have been done.
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*/
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void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *running)
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{
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ktime_t uninitialized_var(starttime), delta, endtime;
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if (!running)
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return;
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if (initcall_debug && system_state == SYSTEM_BOOTING) {
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printk(KERN_DEBUG "async_waiting @ %i\n", task_pid_nr(current));
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starttime = ktime_get();
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}
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wait_event(async_done, lowest_in_progress(running) >= cookie);
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if (initcall_debug && system_state == SYSTEM_BOOTING) {
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endtime = ktime_get();
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delta = ktime_sub(endtime, starttime);
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printk(KERN_DEBUG "async_continuing @ %i after %lli usec\n",
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task_pid_nr(current),
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(long long)ktime_to_ns(delta) >> 10);
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}
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}
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EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
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/**
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* async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
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* @cookie: async_cookie_t to use as checkpoint
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*
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* This function waits until all asynchronous function calls prior to @cookie
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* have been done.
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*/
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void async_synchronize_cookie(async_cookie_t cookie)
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{
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async_synchronize_cookie_domain(cookie, &async_running);
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}
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EXPORT_SYMBOL_GPL(async_synchronize_cookie);
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