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3c5d61ae91
Improve readability of kvfree_rcu_queue_batch() function
in away that, after a first batch queuing, the loop is break
and success value is returned to a caller.
There is no reason to loop and check batches further as all
outstanding objects have already been picked and attached to
a certain batch to complete an offloading.
Fixes: 2b55d6a42d ("rcu/kvfree: Add kvfree_rcu_barrier() API")
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Closes: https://lore.kernel.org/lkml/ZvWUt2oyXRsvJRNc@pc636/T/
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
5751 lines
186 KiB
C
5751 lines
186 KiB
C
// SPDX-License-Identifier: GPL-2.0+
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/*
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* Read-Copy Update mechanism for mutual exclusion (tree-based version)
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*
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* Copyright IBM Corporation, 2008
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*
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* Authors: Dipankar Sarma <dipankar@in.ibm.com>
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* Manfred Spraul <manfred@colorfullife.com>
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* Paul E. McKenney <paulmck@linux.ibm.com>
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*
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* Based on the original work by Paul McKenney <paulmck@linux.ibm.com>
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* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
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*
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* For detailed explanation of Read-Copy Update mechanism see -
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* Documentation/RCU
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*/
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#define pr_fmt(fmt) "rcu: " fmt
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#include <linux/types.h>
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#include <linux/kernel.h>
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#include <linux/init.h>
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#include <linux/spinlock.h>
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#include <linux/smp.h>
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#include <linux/rcupdate_wait.h>
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#include <linux/interrupt.h>
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#include <linux/sched.h>
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#include <linux/sched/debug.h>
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#include <linux/nmi.h>
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#include <linux/atomic.h>
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#include <linux/bitops.h>
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#include <linux/export.h>
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#include <linux/completion.h>
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#include <linux/kmemleak.h>
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#include <linux/moduleparam.h>
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#include <linux/panic.h>
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#include <linux/panic_notifier.h>
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#include <linux/percpu.h>
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#include <linux/notifier.h>
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#include <linux/cpu.h>
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#include <linux/mutex.h>
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#include <linux/time.h>
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#include <linux/kernel_stat.h>
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#include <linux/wait.h>
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#include <linux/kthread.h>
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#include <uapi/linux/sched/types.h>
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#include <linux/prefetch.h>
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#include <linux/delay.h>
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#include <linux/random.h>
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#include <linux/trace_events.h>
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#include <linux/suspend.h>
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#include <linux/ftrace.h>
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#include <linux/tick.h>
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#include <linux/sysrq.h>
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#include <linux/kprobes.h>
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#include <linux/gfp.h>
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#include <linux/oom.h>
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#include <linux/smpboot.h>
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#include <linux/jiffies.h>
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#include <linux/slab.h>
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#include <linux/sched/isolation.h>
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#include <linux/sched/clock.h>
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#include <linux/vmalloc.h>
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#include <linux/mm.h>
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#include <linux/kasan.h>
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#include <linux/context_tracking.h>
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#include "../time/tick-internal.h"
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#include "tree.h"
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#include "rcu.h"
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#ifdef MODULE_PARAM_PREFIX
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#undef MODULE_PARAM_PREFIX
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#endif
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#define MODULE_PARAM_PREFIX "rcutree."
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/* Data structures. */
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static void rcu_sr_normal_gp_cleanup_work(struct work_struct *);
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static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = {
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.gpwrap = true,
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};
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static struct rcu_state rcu_state = {
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.level = { &rcu_state.node[0] },
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.gp_state = RCU_GP_IDLE,
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.gp_seq = (0UL - 300UL) << RCU_SEQ_CTR_SHIFT,
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.barrier_mutex = __MUTEX_INITIALIZER(rcu_state.barrier_mutex),
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.barrier_lock = __RAW_SPIN_LOCK_UNLOCKED(rcu_state.barrier_lock),
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.name = RCU_NAME,
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.abbr = RCU_ABBR,
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.exp_mutex = __MUTEX_INITIALIZER(rcu_state.exp_mutex),
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.exp_wake_mutex = __MUTEX_INITIALIZER(rcu_state.exp_wake_mutex),
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.ofl_lock = __ARCH_SPIN_LOCK_UNLOCKED,
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.srs_cleanup_work = __WORK_INITIALIZER(rcu_state.srs_cleanup_work,
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rcu_sr_normal_gp_cleanup_work),
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.srs_cleanups_pending = ATOMIC_INIT(0),
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#ifdef CONFIG_RCU_NOCB_CPU
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.nocb_mutex = __MUTEX_INITIALIZER(rcu_state.nocb_mutex),
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#endif
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};
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/* Dump rcu_node combining tree at boot to verify correct setup. */
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static bool dump_tree;
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module_param(dump_tree, bool, 0444);
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/* By default, use RCU_SOFTIRQ instead of rcuc kthreads. */
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static bool use_softirq = !IS_ENABLED(CONFIG_PREEMPT_RT);
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#ifndef CONFIG_PREEMPT_RT
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module_param(use_softirq, bool, 0444);
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#endif
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/* Control rcu_node-tree auto-balancing at boot time. */
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static bool rcu_fanout_exact;
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module_param(rcu_fanout_exact, bool, 0444);
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/* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */
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static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
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module_param(rcu_fanout_leaf, int, 0444);
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int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
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/* Number of rcu_nodes at specified level. */
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int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
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int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
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/*
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* The rcu_scheduler_active variable is initialized to the value
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* RCU_SCHEDULER_INACTIVE and transitions RCU_SCHEDULER_INIT just before the
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* first task is spawned. So when this variable is RCU_SCHEDULER_INACTIVE,
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* RCU can assume that there is but one task, allowing RCU to (for example)
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* optimize synchronize_rcu() to a simple barrier(). When this variable
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* is RCU_SCHEDULER_INIT, RCU must actually do all the hard work required
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* to detect real grace periods. This variable is also used to suppress
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* boot-time false positives from lockdep-RCU error checking. Finally, it
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* transitions from RCU_SCHEDULER_INIT to RCU_SCHEDULER_RUNNING after RCU
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* is fully initialized, including all of its kthreads having been spawned.
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*/
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int rcu_scheduler_active __read_mostly;
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EXPORT_SYMBOL_GPL(rcu_scheduler_active);
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/*
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* The rcu_scheduler_fully_active variable transitions from zero to one
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* during the early_initcall() processing, which is after the scheduler
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* is capable of creating new tasks. So RCU processing (for example,
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* creating tasks for RCU priority boosting) must be delayed until after
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* rcu_scheduler_fully_active transitions from zero to one. We also
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* currently delay invocation of any RCU callbacks until after this point.
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*
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* It might later prove better for people registering RCU callbacks during
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* early boot to take responsibility for these callbacks, but one step at
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* a time.
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*/
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static int rcu_scheduler_fully_active __read_mostly;
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static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
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unsigned long gps, unsigned long flags);
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static struct task_struct *rcu_boost_task(struct rcu_node *rnp);
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static void invoke_rcu_core(void);
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static void rcu_report_exp_rdp(struct rcu_data *rdp);
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static void sync_sched_exp_online_cleanup(int cpu);
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static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp);
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static bool rcu_rdp_is_offloaded(struct rcu_data *rdp);
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static bool rcu_rdp_cpu_online(struct rcu_data *rdp);
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static bool rcu_init_invoked(void);
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static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf);
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static void rcu_init_new_rnp(struct rcu_node *rnp_leaf);
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/*
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* rcuc/rcub/rcuop kthread realtime priority. The "rcuop"
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* real-time priority(enabling/disabling) is controlled by
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* the extra CONFIG_RCU_NOCB_CPU_CB_BOOST configuration.
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*/
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static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
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module_param(kthread_prio, int, 0444);
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/* Delay in jiffies for grace-period initialization delays, debug only. */
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static int gp_preinit_delay;
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module_param(gp_preinit_delay, int, 0444);
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static int gp_init_delay;
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module_param(gp_init_delay, int, 0444);
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static int gp_cleanup_delay;
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module_param(gp_cleanup_delay, int, 0444);
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static int nohz_full_patience_delay;
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module_param(nohz_full_patience_delay, int, 0444);
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static int nohz_full_patience_delay_jiffies;
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// Add delay to rcu_read_unlock() for strict grace periods.
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static int rcu_unlock_delay;
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#ifdef CONFIG_RCU_STRICT_GRACE_PERIOD
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module_param(rcu_unlock_delay, int, 0444);
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#endif
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/*
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* This rcu parameter is runtime-read-only. It reflects
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* a minimum allowed number of objects which can be cached
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* per-CPU. Object size is equal to one page. This value
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* can be changed at boot time.
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*/
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static int rcu_min_cached_objs = 5;
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module_param(rcu_min_cached_objs, int, 0444);
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// A page shrinker can ask for pages to be freed to make them
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// available for other parts of the system. This usually happens
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// under low memory conditions, and in that case we should also
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// defer page-cache filling for a short time period.
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//
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// The default value is 5 seconds, which is long enough to reduce
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// interference with the shrinker while it asks other systems to
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// drain their caches.
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static int rcu_delay_page_cache_fill_msec = 5000;
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module_param(rcu_delay_page_cache_fill_msec, int, 0444);
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/* Retrieve RCU kthreads priority for rcutorture */
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int rcu_get_gp_kthreads_prio(void)
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{
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return kthread_prio;
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}
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EXPORT_SYMBOL_GPL(rcu_get_gp_kthreads_prio);
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/*
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* Number of grace periods between delays, normalized by the duration of
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* the delay. The longer the delay, the more the grace periods between
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* each delay. The reason for this normalization is that it means that,
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* for non-zero delays, the overall slowdown of grace periods is constant
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* regardless of the duration of the delay. This arrangement balances
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* the need for long delays to increase some race probabilities with the
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* need for fast grace periods to increase other race probabilities.
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*/
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#define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays for debugging. */
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/*
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* Return true if an RCU grace period is in progress. The READ_ONCE()s
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* permit this function to be invoked without holding the root rcu_node
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* structure's ->lock, but of course results can be subject to change.
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*/
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static int rcu_gp_in_progress(void)
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{
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return rcu_seq_state(rcu_seq_current(&rcu_state.gp_seq));
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}
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/*
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* Return the number of callbacks queued on the specified CPU.
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* Handles both the nocbs and normal cases.
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*/
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static long rcu_get_n_cbs_cpu(int cpu)
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{
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struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
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if (rcu_segcblist_is_enabled(&rdp->cblist))
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return rcu_segcblist_n_cbs(&rdp->cblist);
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return 0;
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}
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/**
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* rcu_softirq_qs - Provide a set of RCU quiescent states in softirq processing
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*
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* Mark a quiescent state for RCU, Tasks RCU, and Tasks Trace RCU.
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* This is a special-purpose function to be used in the softirq
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* infrastructure and perhaps the occasional long-running softirq
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* handler.
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*
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* Note that from RCU's viewpoint, a call to rcu_softirq_qs() is
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* equivalent to momentarily completely enabling preemption. For
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* example, given this code::
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*
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* local_bh_disable();
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* do_something();
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* rcu_softirq_qs(); // A
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* do_something_else();
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* local_bh_enable(); // B
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*
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* A call to synchronize_rcu() that began concurrently with the
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* call to do_something() would be guaranteed to wait only until
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* execution reached statement A. Without that rcu_softirq_qs(),
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* that same synchronize_rcu() would instead be guaranteed to wait
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* until execution reached statement B.
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*/
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void rcu_softirq_qs(void)
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{
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RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
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lock_is_held(&rcu_lock_map) ||
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lock_is_held(&rcu_sched_lock_map),
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"Illegal rcu_softirq_qs() in RCU read-side critical section");
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rcu_qs();
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rcu_preempt_deferred_qs(current);
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rcu_tasks_qs(current, false);
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}
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/*
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* Reset the current CPU's RCU_WATCHING counter to indicate that the
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* newly onlined CPU is no longer in an extended quiescent state.
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* This will either leave the counter unchanged, or increment it
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* to the next non-quiescent value.
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*
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* The non-atomic test/increment sequence works because the upper bits
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* of the ->state variable are manipulated only by the corresponding CPU,
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* or when the corresponding CPU is offline.
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*/
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static void rcu_watching_online(void)
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{
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if (ct_rcu_watching() & CT_RCU_WATCHING)
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return;
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ct_state_inc(CT_RCU_WATCHING);
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}
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/*
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* Return true if the snapshot returned from ct_rcu_watching()
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* indicates that RCU is in an extended quiescent state.
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*/
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static bool rcu_watching_snap_in_eqs(int snap)
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{
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return !(snap & CT_RCU_WATCHING);
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}
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/**
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* rcu_watching_snap_stopped_since() - Has RCU stopped watching a given CPU
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* since the specified @snap?
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*
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* @rdp: The rcu_data corresponding to the CPU for which to check EQS.
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* @snap: rcu_watching snapshot taken when the CPU wasn't in an EQS.
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*
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* Returns true if the CPU corresponding to @rdp has spent some time in an
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* extended quiescent state since @snap. Note that this doesn't check if it
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* /still/ is in an EQS, just that it went through one since @snap.
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*
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* This is meant to be used in a loop waiting for a CPU to go through an EQS.
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*/
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static bool rcu_watching_snap_stopped_since(struct rcu_data *rdp, int snap)
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{
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/*
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* The first failing snapshot is already ordered against the accesses
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* performed by the remote CPU after it exits idle.
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*
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* The second snapshot therefore only needs to order against accesses
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* performed by the remote CPU prior to entering idle and therefore can
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* rely solely on acquire semantics.
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*/
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if (WARN_ON_ONCE(rcu_watching_snap_in_eqs(snap)))
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return true;
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return snap != ct_rcu_watching_cpu_acquire(rdp->cpu);
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}
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/*
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* Return true if the referenced integer is zero while the specified
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* CPU remains within a single extended quiescent state.
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*/
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bool rcu_watching_zero_in_eqs(int cpu, int *vp)
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{
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int snap;
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// If not quiescent, force back to earlier extended quiescent state.
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snap = ct_rcu_watching_cpu(cpu) & ~CT_RCU_WATCHING;
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smp_rmb(); // Order CT state and *vp reads.
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if (READ_ONCE(*vp))
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return false; // Non-zero, so report failure;
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smp_rmb(); // Order *vp read and CT state re-read.
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// If still in the same extended quiescent state, we are good!
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return snap == ct_rcu_watching_cpu(cpu);
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}
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/*
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* Let the RCU core know that this CPU has gone through the scheduler,
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* which is a quiescent state. This is called when the need for a
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* quiescent state is urgent, so we burn an atomic operation and full
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* memory barriers to let the RCU core know about it, regardless of what
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* this CPU might (or might not) do in the near future.
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*
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* We inform the RCU core by emulating a zero-duration dyntick-idle period.
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*
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* The caller must have disabled interrupts and must not be idle.
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*/
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notrace void rcu_momentary_eqs(void)
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{
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int seq;
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raw_cpu_write(rcu_data.rcu_need_heavy_qs, false);
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seq = ct_state_inc(2 * CT_RCU_WATCHING);
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/* It is illegal to call this from idle state. */
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WARN_ON_ONCE(!(seq & CT_RCU_WATCHING));
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rcu_preempt_deferred_qs(current);
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}
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EXPORT_SYMBOL_GPL(rcu_momentary_eqs);
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/**
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* rcu_is_cpu_rrupt_from_idle - see if 'interrupted' from idle
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*
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* If the current CPU is idle and running at a first-level (not nested)
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* interrupt, or directly, from idle, return true.
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*
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* The caller must have at least disabled IRQs.
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*/
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static int rcu_is_cpu_rrupt_from_idle(void)
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{
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long nesting;
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/*
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* Usually called from the tick; but also used from smp_function_call()
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* for expedited grace periods. This latter can result in running from
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* the idle task, instead of an actual IPI.
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*/
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lockdep_assert_irqs_disabled();
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/* Check for counter underflows */
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RCU_LOCKDEP_WARN(ct_nesting() < 0,
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"RCU nesting counter underflow!");
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RCU_LOCKDEP_WARN(ct_nmi_nesting() <= 0,
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"RCU nmi_nesting counter underflow/zero!");
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/* Are we at first interrupt nesting level? */
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nesting = ct_nmi_nesting();
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if (nesting > 1)
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return false;
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/*
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* If we're not in an interrupt, we must be in the idle task!
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*/
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WARN_ON_ONCE(!nesting && !is_idle_task(current));
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/* Does CPU appear to be idle from an RCU standpoint? */
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return ct_nesting() == 0;
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}
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#define DEFAULT_RCU_BLIMIT (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 1000 : 10)
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// Maximum callbacks per rcu_do_batch ...
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#define DEFAULT_MAX_RCU_BLIMIT 10000 // ... even during callback flood.
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static long blimit = DEFAULT_RCU_BLIMIT;
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#define DEFAULT_RCU_QHIMARK 10000 // If this many pending, ignore blimit.
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static long qhimark = DEFAULT_RCU_QHIMARK;
|
||
#define DEFAULT_RCU_QLOMARK 100 // Once only this many pending, use blimit.
|
||
static long qlowmark = DEFAULT_RCU_QLOMARK;
|
||
#define DEFAULT_RCU_QOVLD_MULT 2
|
||
#define DEFAULT_RCU_QOVLD (DEFAULT_RCU_QOVLD_MULT * DEFAULT_RCU_QHIMARK)
|
||
static long qovld = DEFAULT_RCU_QOVLD; // If this many pending, hammer QS.
|
||
static long qovld_calc = -1; // No pre-initialization lock acquisitions!
|
||
|
||
module_param(blimit, long, 0444);
|
||
module_param(qhimark, long, 0444);
|
||
module_param(qlowmark, long, 0444);
|
||
module_param(qovld, long, 0444);
|
||
|
||
static ulong jiffies_till_first_fqs = IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 0 : ULONG_MAX;
|
||
static ulong jiffies_till_next_fqs = ULONG_MAX;
|
||
static bool rcu_kick_kthreads;
|
||
static int rcu_divisor = 7;
|
||
module_param(rcu_divisor, int, 0644);
|
||
|
||
/* Force an exit from rcu_do_batch() after 3 milliseconds. */
|
||
static long rcu_resched_ns = 3 * NSEC_PER_MSEC;
|
||
module_param(rcu_resched_ns, long, 0644);
|
||
|
||
/*
|
||
* How long the grace period must be before we start recruiting
|
||
* quiescent-state help from rcu_note_context_switch().
|
||
*/
|
||
static ulong jiffies_till_sched_qs = ULONG_MAX;
|
||
module_param(jiffies_till_sched_qs, ulong, 0444);
|
||
static ulong jiffies_to_sched_qs; /* See adjust_jiffies_till_sched_qs(). */
|
||
module_param(jiffies_to_sched_qs, ulong, 0444); /* Display only! */
|
||
|
||
/*
|
||
* Make sure that we give the grace-period kthread time to detect any
|
||
* idle CPUs before taking active measures to force quiescent states.
|
||
* However, don't go below 100 milliseconds, adjusted upwards for really
|
||
* large systems.
|
||
*/
|
||
static void adjust_jiffies_till_sched_qs(void)
|
||
{
|
||
unsigned long j;
|
||
|
||
/* If jiffies_till_sched_qs was specified, respect the request. */
|
||
if (jiffies_till_sched_qs != ULONG_MAX) {
|
||
WRITE_ONCE(jiffies_to_sched_qs, jiffies_till_sched_qs);
|
||
return;
|
||
}
|
||
/* Otherwise, set to third fqs scan, but bound below on large system. */
|
||
j = READ_ONCE(jiffies_till_first_fqs) +
|
||
2 * READ_ONCE(jiffies_till_next_fqs);
|
||
if (j < HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV)
|
||
j = HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
|
||
pr_info("RCU calculated value of scheduler-enlistment delay is %ld jiffies.\n", j);
|
||
WRITE_ONCE(jiffies_to_sched_qs, j);
|
||
}
|
||
|
||
static int param_set_first_fqs_jiffies(const char *val, const struct kernel_param *kp)
|
||
{
|
||
ulong j;
|
||
int ret = kstrtoul(val, 0, &j);
|
||
|
||
if (!ret) {
|
||
WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : j);
|
||
adjust_jiffies_till_sched_qs();
|
||
}
|
||
return ret;
|
||
}
|
||
|
||
static int param_set_next_fqs_jiffies(const char *val, const struct kernel_param *kp)
|
||
{
|
||
ulong j;
|
||
int ret = kstrtoul(val, 0, &j);
|
||
|
||
if (!ret) {
|
||
WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : (j ?: 1));
|
||
adjust_jiffies_till_sched_qs();
|
||
}
|
||
return ret;
|
||
}
|
||
|
||
static const struct kernel_param_ops first_fqs_jiffies_ops = {
|
||
.set = param_set_first_fqs_jiffies,
|
||
.get = param_get_ulong,
|
||
};
|
||
|
||
static const struct kernel_param_ops next_fqs_jiffies_ops = {
|
||
.set = param_set_next_fqs_jiffies,
|
||
.get = param_get_ulong,
|
||
};
|
||
|
||
module_param_cb(jiffies_till_first_fqs, &first_fqs_jiffies_ops, &jiffies_till_first_fqs, 0644);
|
||
module_param_cb(jiffies_till_next_fqs, &next_fqs_jiffies_ops, &jiffies_till_next_fqs, 0644);
|
||
module_param(rcu_kick_kthreads, bool, 0644);
|
||
|
||
static void force_qs_rnp(int (*f)(struct rcu_data *rdp));
|
||
static int rcu_pending(int user);
|
||
|
||
/*
|
||
* Return the number of RCU GPs completed thus far for debug & stats.
|
||
*/
|
||
unsigned long rcu_get_gp_seq(void)
|
||
{
|
||
return READ_ONCE(rcu_state.gp_seq);
|
||
}
|
||
EXPORT_SYMBOL_GPL(rcu_get_gp_seq);
|
||
|
||
/*
|
||
* Return the number of RCU expedited batches completed thus far for
|
||
* debug & stats. Odd numbers mean that a batch is in progress, even
|
||
* numbers mean idle. The value returned will thus be roughly double
|
||
* the cumulative batches since boot.
|
||
*/
|
||
unsigned long rcu_exp_batches_completed(void)
|
||
{
|
||
return rcu_state.expedited_sequence;
|
||
}
|
||
EXPORT_SYMBOL_GPL(rcu_exp_batches_completed);
|
||
|
||
/*
|
||
* Return the root node of the rcu_state structure.
|
||
*/
|
||
static struct rcu_node *rcu_get_root(void)
|
||
{
|
||
return &rcu_state.node[0];
|
||
}
|
||
|
||
/*
|
||
* Send along grace-period-related data for rcutorture diagnostics.
|
||
*/
|
||
void rcutorture_get_gp_data(int *flags, unsigned long *gp_seq)
|
||
{
|
||
*flags = READ_ONCE(rcu_state.gp_flags);
|
||
*gp_seq = rcu_seq_current(&rcu_state.gp_seq);
|
||
}
|
||
EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
|
||
|
||
#if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK))
|
||
/*
|
||
* An empty function that will trigger a reschedule on
|
||
* IRQ tail once IRQs get re-enabled on userspace/guest resume.
|
||
*/
|
||
static void late_wakeup_func(struct irq_work *work)
|
||
{
|
||
}
|
||
|
||
static DEFINE_PER_CPU(struct irq_work, late_wakeup_work) =
|
||
IRQ_WORK_INIT(late_wakeup_func);
|
||
|
||
/*
|
||
* If either:
|
||
*
|
||
* 1) the task is about to enter in guest mode and $ARCH doesn't support KVM generic work
|
||
* 2) the task is about to enter in user mode and $ARCH doesn't support generic entry.
|
||
*
|
||
* In these cases the late RCU wake ups aren't supported in the resched loops and our
|
||
* last resort is to fire a local irq_work that will trigger a reschedule once IRQs
|
||
* get re-enabled again.
|
||
*/
|
||
noinstr void rcu_irq_work_resched(void)
|
||
{
|
||
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
|
||
|
||
if (IS_ENABLED(CONFIG_GENERIC_ENTRY) && !(current->flags & PF_VCPU))
|
||
return;
|
||
|
||
if (IS_ENABLED(CONFIG_KVM_XFER_TO_GUEST_WORK) && (current->flags & PF_VCPU))
|
||
return;
|
||
|
||
instrumentation_begin();
|
||
if (do_nocb_deferred_wakeup(rdp) && need_resched()) {
|
||
irq_work_queue(this_cpu_ptr(&late_wakeup_work));
|
||
}
|
||
instrumentation_end();
|
||
}
|
||
#endif /* #if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK)) */
|
||
|
||
#ifdef CONFIG_PROVE_RCU
|
||
/**
|
||
* rcu_irq_exit_check_preempt - Validate that scheduling is possible
|
||
*/
|
||
void rcu_irq_exit_check_preempt(void)
|
||
{
|
||
lockdep_assert_irqs_disabled();
|
||
|
||
RCU_LOCKDEP_WARN(ct_nesting() <= 0,
|
||
"RCU nesting counter underflow/zero!");
|
||
RCU_LOCKDEP_WARN(ct_nmi_nesting() !=
|
||
CT_NESTING_IRQ_NONIDLE,
|
||
"Bad RCU nmi_nesting counter\n");
|
||
RCU_LOCKDEP_WARN(!rcu_is_watching_curr_cpu(),
|
||
"RCU in extended quiescent state!");
|
||
}
|
||
#endif /* #ifdef CONFIG_PROVE_RCU */
|
||
|
||
#ifdef CONFIG_NO_HZ_FULL
|
||
/**
|
||
* __rcu_irq_enter_check_tick - Enable scheduler tick on CPU if RCU needs it.
|
||
*
|
||
* The scheduler tick is not normally enabled when CPUs enter the kernel
|
||
* from nohz_full userspace execution. After all, nohz_full userspace
|
||
* execution is an RCU quiescent state and the time executing in the kernel
|
||
* is quite short. Except of course when it isn't. And it is not hard to
|
||
* cause a large system to spend tens of seconds or even minutes looping
|
||
* in the kernel, which can cause a number of problems, include RCU CPU
|
||
* stall warnings.
|
||
*
|
||
* Therefore, if a nohz_full CPU fails to report a quiescent state
|
||
* in a timely manner, the RCU grace-period kthread sets that CPU's
|
||
* ->rcu_urgent_qs flag with the expectation that the next interrupt or
|
||
* exception will invoke this function, which will turn on the scheduler
|
||
* tick, which will enable RCU to detect that CPU's quiescent states,
|
||
* for example, due to cond_resched() calls in CONFIG_PREEMPT=n kernels.
|
||
* The tick will be disabled once a quiescent state is reported for
|
||
* this CPU.
|
||
*
|
||
* Of course, in carefully tuned systems, there might never be an
|
||
* interrupt or exception. In that case, the RCU grace-period kthread
|
||
* will eventually cause one to happen. However, in less carefully
|
||
* controlled environments, this function allows RCU to get what it
|
||
* needs without creating otherwise useless interruptions.
|
||
*/
|
||
void __rcu_irq_enter_check_tick(void)
|
||
{
|
||
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
|
||
|
||
// If we're here from NMI there's nothing to do.
|
||
if (in_nmi())
|
||
return;
|
||
|
||
RCU_LOCKDEP_WARN(!rcu_is_watching_curr_cpu(),
|
||
"Illegal rcu_irq_enter_check_tick() from extended quiescent state");
|
||
|
||
if (!tick_nohz_full_cpu(rdp->cpu) ||
|
||
!READ_ONCE(rdp->rcu_urgent_qs) ||
|
||
READ_ONCE(rdp->rcu_forced_tick)) {
|
||
// RCU doesn't need nohz_full help from this CPU, or it is
|
||
// already getting that help.
|
||
return;
|
||
}
|
||
|
||
// We get here only when not in an extended quiescent state and
|
||
// from interrupts (as opposed to NMIs). Therefore, (1) RCU is
|
||
// already watching and (2) The fact that we are in an interrupt
|
||
// handler and that the rcu_node lock is an irq-disabled lock
|
||
// prevents self-deadlock. So we can safely recheck under the lock.
|
||
// Note that the nohz_full state currently cannot change.
|
||
raw_spin_lock_rcu_node(rdp->mynode);
|
||
if (READ_ONCE(rdp->rcu_urgent_qs) && !rdp->rcu_forced_tick) {
|
||
// A nohz_full CPU is in the kernel and RCU needs a
|
||
// quiescent state. Turn on the tick!
|
||
WRITE_ONCE(rdp->rcu_forced_tick, true);
|
||
tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
|
||
}
|
||
raw_spin_unlock_rcu_node(rdp->mynode);
|
||
}
|
||
NOKPROBE_SYMBOL(__rcu_irq_enter_check_tick);
|
||
#endif /* CONFIG_NO_HZ_FULL */
|
||
|
||
/*
|
||
* Check to see if any future non-offloaded RCU-related work will need
|
||
* to be done by the current CPU, even if none need be done immediately,
|
||
* returning 1 if so. This function is part of the RCU implementation;
|
||
* it is -not- an exported member of the RCU API. This is used by
|
||
* the idle-entry code to figure out whether it is safe to disable the
|
||
* scheduler-clock interrupt.
|
||
*
|
||
* Just check whether or not this CPU has non-offloaded RCU callbacks
|
||
* queued.
|
||
*/
|
||
int rcu_needs_cpu(void)
|
||
{
|
||
return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) &&
|
||
!rcu_rdp_is_offloaded(this_cpu_ptr(&rcu_data));
|
||
}
|
||
|
||
/*
|
||
* If any sort of urgency was applied to the current CPU (for example,
|
||
* the scheduler-clock interrupt was enabled on a nohz_full CPU) in order
|
||
* to get to a quiescent state, disable it.
|
||
*/
|
||
static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp)
|
||
{
|
||
raw_lockdep_assert_held_rcu_node(rdp->mynode);
|
||
WRITE_ONCE(rdp->rcu_urgent_qs, false);
|
||
WRITE_ONCE(rdp->rcu_need_heavy_qs, false);
|
||
if (tick_nohz_full_cpu(rdp->cpu) && rdp->rcu_forced_tick) {
|
||
tick_dep_clear_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
|
||
WRITE_ONCE(rdp->rcu_forced_tick, false);
|
||
}
|
||
}
|
||
|
||
/**
|
||
* rcu_is_watching - RCU read-side critical sections permitted on current CPU?
|
||
*
|
||
* Return @true if RCU is watching the running CPU and @false otherwise.
|
||
* An @true return means that this CPU can safely enter RCU read-side
|
||
* critical sections.
|
||
*
|
||
* Although calls to rcu_is_watching() from most parts of the kernel
|
||
* will return @true, there are important exceptions. For example, if the
|
||
* current CPU is deep within its idle loop, in kernel entry/exit code,
|
||
* or offline, rcu_is_watching() will return @false.
|
||
*
|
||
* Make notrace because it can be called by the internal functions of
|
||
* ftrace, and making this notrace removes unnecessary recursion calls.
|
||
*/
|
||
notrace bool rcu_is_watching(void)
|
||
{
|
||
bool ret;
|
||
|
||
preempt_disable_notrace();
|
||
ret = rcu_is_watching_curr_cpu();
|
||
preempt_enable_notrace();
|
||
return ret;
|
||
}
|
||
EXPORT_SYMBOL_GPL(rcu_is_watching);
|
||
|
||
/*
|
||
* If a holdout task is actually running, request an urgent quiescent
|
||
* state from its CPU. This is unsynchronized, so migrations can cause
|
||
* the request to go to the wrong CPU. Which is OK, all that will happen
|
||
* is that the CPU's next context switch will be a bit slower and next
|
||
* time around this task will generate another request.
|
||
*/
|
||
void rcu_request_urgent_qs_task(struct task_struct *t)
|
||
{
|
||
int cpu;
|
||
|
||
barrier();
|
||
cpu = task_cpu(t);
|
||
if (!task_curr(t))
|
||
return; /* This task is not running on that CPU. */
|
||
smp_store_release(per_cpu_ptr(&rcu_data.rcu_urgent_qs, cpu), true);
|
||
}
|
||
|
||
/*
|
||
* When trying to report a quiescent state on behalf of some other CPU,
|
||
* it is our responsibility to check for and handle potential overflow
|
||
* of the rcu_node ->gp_seq counter with respect to the rcu_data counters.
|
||
* After all, the CPU might be in deep idle state, and thus executing no
|
||
* code whatsoever.
|
||
*/
|
||
static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp)
|
||
{
|
||
raw_lockdep_assert_held_rcu_node(rnp);
|
||
if (ULONG_CMP_LT(rcu_seq_current(&rdp->gp_seq) + ULONG_MAX / 4,
|
||
rnp->gp_seq))
|
||
WRITE_ONCE(rdp->gpwrap, true);
|
||
if (ULONG_CMP_LT(rdp->rcu_iw_gp_seq + ULONG_MAX / 4, rnp->gp_seq))
|
||
rdp->rcu_iw_gp_seq = rnp->gp_seq + ULONG_MAX / 4;
|
||
}
|
||
|
||
/*
|
||
* Snapshot the specified CPU's RCU_WATCHING counter so that we can later
|
||
* credit them with an implicit quiescent state. Return 1 if this CPU
|
||
* is in dynticks idle mode, which is an extended quiescent state.
|
||
*/
|
||
static int rcu_watching_snap_save(struct rcu_data *rdp)
|
||
{
|
||
/*
|
||
* Full ordering between remote CPU's post idle accesses and updater's
|
||
* accesses prior to current GP (and also the started GP sequence number)
|
||
* is enforced by rcu_seq_start() implicit barrier and even further by
|
||
* smp_mb__after_unlock_lock() barriers chained all the way throughout the
|
||
* rnp locking tree since rcu_gp_init() and up to the current leaf rnp
|
||
* locking.
|
||
*
|
||
* Ordering between remote CPU's pre idle accesses and post grace period
|
||
* updater's accesses is enforced by the below acquire semantic.
|
||
*/
|
||
rdp->watching_snap = ct_rcu_watching_cpu_acquire(rdp->cpu);
|
||
if (rcu_watching_snap_in_eqs(rdp->watching_snap)) {
|
||
trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
|
||
rcu_gpnum_ovf(rdp->mynode, rdp);
|
||
return 1;
|
||
}
|
||
return 0;
|
||
}
|
||
|
||
/*
|
||
* Returns positive if the specified CPU has passed through a quiescent state
|
||
* by virtue of being in or having passed through an dynticks idle state since
|
||
* the last call to rcu_watching_snap_save() for this same CPU, or by
|
||
* virtue of having been offline.
|
||
*
|
||
* Returns negative if the specified CPU needs a force resched.
|
||
*
|
||
* Returns zero otherwise.
|
||
*/
|
||
static int rcu_watching_snap_recheck(struct rcu_data *rdp)
|
||
{
|
||
unsigned long jtsq;
|
||
int ret = 0;
|
||
struct rcu_node *rnp = rdp->mynode;
|
||
|
||
/*
|
||
* If the CPU passed through or entered a dynticks idle phase with
|
||
* no active irq/NMI handlers, then we can safely pretend that the CPU
|
||
* already acknowledged the request to pass through a quiescent
|
||
* state. Either way, that CPU cannot possibly be in an RCU
|
||
* read-side critical section that started before the beginning
|
||
* of the current RCU grace period.
|
||
*/
|
||
if (rcu_watching_snap_stopped_since(rdp, rdp->watching_snap)) {
|
||
trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
|
||
rcu_gpnum_ovf(rnp, rdp);
|
||
return 1;
|
||
}
|
||
|
||
/*
|
||
* Complain if a CPU that is considered to be offline from RCU's
|
||
* perspective has not yet reported a quiescent state. After all,
|
||
* the offline CPU should have reported a quiescent state during
|
||
* the CPU-offline process, or, failing that, by rcu_gp_init()
|
||
* if it ran concurrently with either the CPU going offline or the
|
||
* last task on a leaf rcu_node structure exiting its RCU read-side
|
||
* critical section while all CPUs corresponding to that structure
|
||
* are offline. This added warning detects bugs in any of these
|
||
* code paths.
|
||
*
|
||
* The rcu_node structure's ->lock is held here, which excludes
|
||
* the relevant portions the CPU-hotplug code, the grace-period
|
||
* initialization code, and the rcu_read_unlock() code paths.
|
||
*
|
||
* For more detail, please refer to the "Hotplug CPU" section
|
||
* of RCU's Requirements documentation.
|
||
*/
|
||
if (WARN_ON_ONCE(!rcu_rdp_cpu_online(rdp))) {
|
||
struct rcu_node *rnp1;
|
||
|
||
pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
|
||
__func__, rnp->grplo, rnp->grphi, rnp->level,
|
||
(long)rnp->gp_seq, (long)rnp->completedqs);
|
||
for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
|
||
pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx ->rcu_gp_init_mask %#lx\n",
|
||
__func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext, rnp1->rcu_gp_init_mask);
|
||
pr_info("%s %d: %c online: %ld(%d) offline: %ld(%d)\n",
|
||
__func__, rdp->cpu, ".o"[rcu_rdp_cpu_online(rdp)],
|
||
(long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_state,
|
||
(long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_state);
|
||
return 1; /* Break things loose after complaining. */
|
||
}
|
||
|
||
/*
|
||
* A CPU running for an extended time within the kernel can
|
||
* delay RCU grace periods: (1) At age jiffies_to_sched_qs,
|
||
* set .rcu_urgent_qs, (2) At age 2*jiffies_to_sched_qs, set
|
||
* both .rcu_need_heavy_qs and .rcu_urgent_qs. Note that the
|
||
* unsynchronized assignments to the per-CPU rcu_need_heavy_qs
|
||
* variable are safe because the assignments are repeated if this
|
||
* CPU failed to pass through a quiescent state. This code
|
||
* also checks .jiffies_resched in case jiffies_to_sched_qs
|
||
* is set way high.
|
||
*/
|
||
jtsq = READ_ONCE(jiffies_to_sched_qs);
|
||
if (!READ_ONCE(rdp->rcu_need_heavy_qs) &&
|
||
(time_after(jiffies, rcu_state.gp_start + jtsq * 2) ||
|
||
time_after(jiffies, rcu_state.jiffies_resched) ||
|
||
rcu_state.cbovld)) {
|
||
WRITE_ONCE(rdp->rcu_need_heavy_qs, true);
|
||
/* Store rcu_need_heavy_qs before rcu_urgent_qs. */
|
||
smp_store_release(&rdp->rcu_urgent_qs, true);
|
||
} else if (time_after(jiffies, rcu_state.gp_start + jtsq)) {
|
||
WRITE_ONCE(rdp->rcu_urgent_qs, true);
|
||
}
|
||
|
||
/*
|
||
* NO_HZ_FULL CPUs can run in-kernel without rcu_sched_clock_irq!
|
||
* The above code handles this, but only for straight cond_resched().
|
||
* And some in-kernel loops check need_resched() before calling
|
||
* cond_resched(), which defeats the above code for CPUs that are
|
||
* running in-kernel with scheduling-clock interrupts disabled.
|
||
* So hit them over the head with the resched_cpu() hammer!
|
||
*/
|
||
if (tick_nohz_full_cpu(rdp->cpu) &&
|
||
(time_after(jiffies, READ_ONCE(rdp->last_fqs_resched) + jtsq * 3) ||
|
||
rcu_state.cbovld)) {
|
||
WRITE_ONCE(rdp->rcu_urgent_qs, true);
|
||
WRITE_ONCE(rdp->last_fqs_resched, jiffies);
|
||
ret = -1;
|
||
}
|
||
|
||
/*
|
||
* If more than halfway to RCU CPU stall-warning time, invoke
|
||
* resched_cpu() more frequently to try to loosen things up a bit.
|
||
* Also check to see if the CPU is getting hammered with interrupts,
|
||
* but only once per grace period, just to keep the IPIs down to
|
||
* a dull roar.
|
||
*/
|
||
if (time_after(jiffies, rcu_state.jiffies_resched)) {
|
||
if (time_after(jiffies,
|
||
READ_ONCE(rdp->last_fqs_resched) + jtsq)) {
|
||
WRITE_ONCE(rdp->last_fqs_resched, jiffies);
|
||
ret = -1;
|
||
}
|
||
if (IS_ENABLED(CONFIG_IRQ_WORK) &&
|
||
!rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq &&
|
||
(rnp->ffmask & rdp->grpmask)) {
|
||
rdp->rcu_iw_pending = true;
|
||
rdp->rcu_iw_gp_seq = rnp->gp_seq;
|
||
irq_work_queue_on(&rdp->rcu_iw, rdp->cpu);
|
||
}
|
||
|
||
if (rcu_cpu_stall_cputime && rdp->snap_record.gp_seq != rdp->gp_seq) {
|
||
int cpu = rdp->cpu;
|
||
struct rcu_snap_record *rsrp;
|
||
struct kernel_cpustat *kcsp;
|
||
|
||
kcsp = &kcpustat_cpu(cpu);
|
||
|
||
rsrp = &rdp->snap_record;
|
||
rsrp->cputime_irq = kcpustat_field(kcsp, CPUTIME_IRQ, cpu);
|
||
rsrp->cputime_softirq = kcpustat_field(kcsp, CPUTIME_SOFTIRQ, cpu);
|
||
rsrp->cputime_system = kcpustat_field(kcsp, CPUTIME_SYSTEM, cpu);
|
||
rsrp->nr_hardirqs = kstat_cpu_irqs_sum(rdp->cpu);
|
||
rsrp->nr_softirqs = kstat_cpu_softirqs_sum(rdp->cpu);
|
||
rsrp->nr_csw = nr_context_switches_cpu(rdp->cpu);
|
||
rsrp->jiffies = jiffies;
|
||
rsrp->gp_seq = rdp->gp_seq;
|
||
}
|
||
}
|
||
|
||
return ret;
|
||
}
|
||
|
||
/* Trace-event wrapper function for trace_rcu_future_grace_period. */
|
||
static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
|
||
unsigned long gp_seq_req, const char *s)
|
||
{
|
||
trace_rcu_future_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
|
||
gp_seq_req, rnp->level,
|
||
rnp->grplo, rnp->grphi, s);
|
||
}
|
||
|
||
/*
|
||
* rcu_start_this_gp - Request the start of a particular grace period
|
||
* @rnp_start: The leaf node of the CPU from which to start.
|
||
* @rdp: The rcu_data corresponding to the CPU from which to start.
|
||
* @gp_seq_req: The gp_seq of the grace period to start.
|
||
*
|
||
* Start the specified grace period, as needed to handle newly arrived
|
||
* callbacks. The required future grace periods are recorded in each
|
||
* rcu_node structure's ->gp_seq_needed field. Returns true if there
|
||
* is reason to awaken the grace-period kthread.
|
||
*
|
||
* The caller must hold the specified rcu_node structure's ->lock, which
|
||
* is why the caller is responsible for waking the grace-period kthread.
|
||
*
|
||
* Returns true if the GP thread needs to be awakened else false.
|
||
*/
|
||
static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp,
|
||
unsigned long gp_seq_req)
|
||
{
|
||
bool ret = false;
|
||
struct rcu_node *rnp;
|
||
|
||
/*
|
||
* Use funnel locking to either acquire the root rcu_node
|
||
* structure's lock or bail out if the need for this grace period
|
||
* has already been recorded -- or if that grace period has in
|
||
* fact already started. If there is already a grace period in
|
||
* progress in a non-leaf node, no recording is needed because the
|
||
* end of the grace period will scan the leaf rcu_node structures.
|
||
* Note that rnp_start->lock must not be released.
|
||
*/
|
||
raw_lockdep_assert_held_rcu_node(rnp_start);
|
||
trace_rcu_this_gp(rnp_start, rdp, gp_seq_req, TPS("Startleaf"));
|
||
for (rnp = rnp_start; 1; rnp = rnp->parent) {
|
||
if (rnp != rnp_start)
|
||
raw_spin_lock_rcu_node(rnp);
|
||
if (ULONG_CMP_GE(rnp->gp_seq_needed, gp_seq_req) ||
|
||
rcu_seq_started(&rnp->gp_seq, gp_seq_req) ||
|
||
(rnp != rnp_start &&
|
||
rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))) {
|
||
trace_rcu_this_gp(rnp, rdp, gp_seq_req,
|
||
TPS("Prestarted"));
|
||
goto unlock_out;
|
||
}
|
||
WRITE_ONCE(rnp->gp_seq_needed, gp_seq_req);
|
||
if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) {
|
||
/*
|
||
* We just marked the leaf or internal node, and a
|
||
* grace period is in progress, which means that
|
||
* rcu_gp_cleanup() will see the marking. Bail to
|
||
* reduce contention.
|
||
*/
|
||
trace_rcu_this_gp(rnp_start, rdp, gp_seq_req,
|
||
TPS("Startedleaf"));
|
||
goto unlock_out;
|
||
}
|
||
if (rnp != rnp_start && rnp->parent != NULL)
|
||
raw_spin_unlock_rcu_node(rnp);
|
||
if (!rnp->parent)
|
||
break; /* At root, and perhaps also leaf. */
|
||
}
|
||
|
||
/* If GP already in progress, just leave, otherwise start one. */
|
||
if (rcu_gp_in_progress()) {
|
||
trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedleafroot"));
|
||
goto unlock_out;
|
||
}
|
||
trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot"));
|
||
WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_INIT);
|
||
WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
|
||
if (!READ_ONCE(rcu_state.gp_kthread)) {
|
||
trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));
|
||
goto unlock_out;
|
||
}
|
||
trace_rcu_grace_period(rcu_state.name, data_race(rcu_state.gp_seq), TPS("newreq"));
|
||
ret = true; /* Caller must wake GP kthread. */
|
||
unlock_out:
|
||
/* Push furthest requested GP to leaf node and rcu_data structure. */
|
||
if (ULONG_CMP_LT(gp_seq_req, rnp->gp_seq_needed)) {
|
||
WRITE_ONCE(rnp_start->gp_seq_needed, rnp->gp_seq_needed);
|
||
WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);
|
||
}
|
||
if (rnp != rnp_start)
|
||
raw_spin_unlock_rcu_node(rnp);
|
||
return ret;
|
||
}
|
||
|
||
/*
|
||
* Clean up any old requests for the just-ended grace period. Also return
|
||
* whether any additional grace periods have been requested.
|
||
*/
|
||
static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
|
||
{
|
||
bool needmore;
|
||
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
|
||
|
||
needmore = ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed);
|
||
if (!needmore)
|
||
rnp->gp_seq_needed = rnp->gp_seq; /* Avoid counter wrap. */
|
||
trace_rcu_this_gp(rnp, rdp, rnp->gp_seq,
|
||
needmore ? TPS("CleanupMore") : TPS("Cleanup"));
|
||
return needmore;
|
||
}
|
||
|
||
static void swake_up_one_online_ipi(void *arg)
|
||
{
|
||
struct swait_queue_head *wqh = arg;
|
||
|
||
swake_up_one(wqh);
|
||
}
|
||
|
||
static void swake_up_one_online(struct swait_queue_head *wqh)
|
||
{
|
||
int cpu = get_cpu();
|
||
|
||
/*
|
||
* If called from rcutree_report_cpu_starting(), wake up
|
||
* is dangerous that late in the CPU-down hotplug process. The
|
||
* scheduler might queue an ignored hrtimer. Defer the wake up
|
||
* to an online CPU instead.
|
||
*/
|
||
if (unlikely(cpu_is_offline(cpu))) {
|
||
int target;
|
||
|
||
target = cpumask_any_and(housekeeping_cpumask(HK_TYPE_RCU),
|
||
cpu_online_mask);
|
||
|
||
smp_call_function_single(target, swake_up_one_online_ipi,
|
||
wqh, 0);
|
||
put_cpu();
|
||
} else {
|
||
put_cpu();
|
||
swake_up_one(wqh);
|
||
}
|
||
}
|
||
|
||
/*
|
||
* Awaken the grace-period kthread. Don't do a self-awaken (unless in an
|
||
* interrupt or softirq handler, in which case we just might immediately
|
||
* sleep upon return, resulting in a grace-period hang), and don't bother
|
||
* awakening when there is nothing for the grace-period kthread to do
|
||
* (as in several CPUs raced to awaken, we lost), and finally don't try
|
||
* to awaken a kthread that has not yet been created. If all those checks
|
||
* are passed, track some debug information and awaken.
|
||
*
|
||
* So why do the self-wakeup when in an interrupt or softirq handler
|
||
* in the grace-period kthread's context? Because the kthread might have
|
||
* been interrupted just as it was going to sleep, and just after the final
|
||
* pre-sleep check of the awaken condition. In this case, a wakeup really
|
||
* is required, and is therefore supplied.
|
||
*/
|
||
static void rcu_gp_kthread_wake(void)
|
||
{
|
||
struct task_struct *t = READ_ONCE(rcu_state.gp_kthread);
|
||
|
||
if ((current == t && !in_hardirq() && !in_serving_softirq()) ||
|
||
!READ_ONCE(rcu_state.gp_flags) || !t)
|
||
return;
|
||
WRITE_ONCE(rcu_state.gp_wake_time, jiffies);
|
||
WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq));
|
||
swake_up_one_online(&rcu_state.gp_wq);
|
||
}
|
||
|
||
/*
|
||
* If there is room, assign a ->gp_seq number to any callbacks on this
|
||
* CPU that have not already been assigned. Also accelerate any callbacks
|
||
* that were previously assigned a ->gp_seq number that has since proven
|
||
* to be too conservative, which can happen if callbacks get assigned a
|
||
* ->gp_seq number while RCU is idle, but with reference to a non-root
|
||
* rcu_node structure. This function is idempotent, so it does not hurt
|
||
* to call it repeatedly. Returns an flag saying that we should awaken
|
||
* the RCU grace-period kthread.
|
||
*
|
||
* The caller must hold rnp->lock with interrupts disabled.
|
||
*/
|
||
static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
|
||
{
|
||
unsigned long gp_seq_req;
|
||
bool ret = false;
|
||
|
||
rcu_lockdep_assert_cblist_protected(rdp);
|
||
raw_lockdep_assert_held_rcu_node(rnp);
|
||
|
||
/* If no pending (not yet ready to invoke) callbacks, nothing to do. */
|
||
if (!rcu_segcblist_pend_cbs(&rdp->cblist))
|
||
return false;
|
||
|
||
trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPreAcc"));
|
||
|
||
/*
|
||
* Callbacks are often registered with incomplete grace-period
|
||
* information. Something about the fact that getting exact
|
||
* information requires acquiring a global lock... RCU therefore
|
||
* makes a conservative estimate of the grace period number at which
|
||
* a given callback will become ready to invoke. The following
|
||
* code checks this estimate and improves it when possible, thus
|
||
* accelerating callback invocation to an earlier grace-period
|
||
* number.
|
||
*/
|
||
gp_seq_req = rcu_seq_snap(&rcu_state.gp_seq);
|
||
if (rcu_segcblist_accelerate(&rdp->cblist, gp_seq_req))
|
||
ret = rcu_start_this_gp(rnp, rdp, gp_seq_req);
|
||
|
||
/* Trace depending on how much we were able to accelerate. */
|
||
if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
|
||
trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccWaitCB"));
|
||
else
|
||
trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccReadyCB"));
|
||
|
||
trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPostAcc"));
|
||
|
||
return ret;
|
||
}
|
||
|
||
/*
|
||
* Similar to rcu_accelerate_cbs(), but does not require that the leaf
|
||
* rcu_node structure's ->lock be held. It consults the cached value
|
||
* of ->gp_seq_needed in the rcu_data structure, and if that indicates
|
||
* that a new grace-period request be made, invokes rcu_accelerate_cbs()
|
||
* while holding the leaf rcu_node structure's ->lock.
|
||
*/
|
||
static void rcu_accelerate_cbs_unlocked(struct rcu_node *rnp,
|
||
struct rcu_data *rdp)
|
||
{
|
||
unsigned long c;
|
||
bool needwake;
|
||
|
||
rcu_lockdep_assert_cblist_protected(rdp);
|
||
c = rcu_seq_snap(&rcu_state.gp_seq);
|
||
if (!READ_ONCE(rdp->gpwrap) && ULONG_CMP_GE(rdp->gp_seq_needed, c)) {
|
||
/* Old request still live, so mark recent callbacks. */
|
||
(void)rcu_segcblist_accelerate(&rdp->cblist, c);
|
||
return;
|
||
}
|
||
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
|
||
needwake = rcu_accelerate_cbs(rnp, rdp);
|
||
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
|
||
if (needwake)
|
||
rcu_gp_kthread_wake();
|
||
}
|
||
|
||
/*
|
||
* Move any callbacks whose grace period has completed to the
|
||
* RCU_DONE_TAIL sublist, then compact the remaining sublists and
|
||
* assign ->gp_seq numbers to any callbacks in the RCU_NEXT_TAIL
|
||
* sublist. This function is idempotent, so it does not hurt to
|
||
* invoke it repeatedly. As long as it is not invoked -too- often...
|
||
* Returns true if the RCU grace-period kthread needs to be awakened.
|
||
*
|
||
* The caller must hold rnp->lock with interrupts disabled.
|
||
*/
|
||
static bool rcu_advance_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
|
||
{
|
||
rcu_lockdep_assert_cblist_protected(rdp);
|
||
raw_lockdep_assert_held_rcu_node(rnp);
|
||
|
||
/* If no pending (not yet ready to invoke) callbacks, nothing to do. */
|
||
if (!rcu_segcblist_pend_cbs(&rdp->cblist))
|
||
return false;
|
||
|
||
/*
|
||
* Find all callbacks whose ->gp_seq numbers indicate that they
|
||
* are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
|
||
*/
|
||
rcu_segcblist_advance(&rdp->cblist, rnp->gp_seq);
|
||
|
||
/* Classify any remaining callbacks. */
|
||
return rcu_accelerate_cbs(rnp, rdp);
|
||
}
|
||
|
||
/*
|
||
* Move and classify callbacks, but only if doing so won't require
|
||
* that the RCU grace-period kthread be awakened.
|
||
*/
|
||
static void __maybe_unused rcu_advance_cbs_nowake(struct rcu_node *rnp,
|
||
struct rcu_data *rdp)
|
||
{
|
||
rcu_lockdep_assert_cblist_protected(rdp);
|
||
if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) || !raw_spin_trylock_rcu_node(rnp))
|
||
return;
|
||
// The grace period cannot end while we hold the rcu_node lock.
|
||
if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))
|
||
WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp));
|
||
raw_spin_unlock_rcu_node(rnp);
|
||
}
|
||
|
||
/*
|
||
* In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, attempt to generate a
|
||
* quiescent state. This is intended to be invoked when the CPU notices
|
||
* a new grace period.
|
||
*/
|
||
static void rcu_strict_gp_check_qs(void)
|
||
{
|
||
if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) {
|
||
rcu_read_lock();
|
||
rcu_read_unlock();
|
||
}
|
||
}
|
||
|
||
/*
|
||
* Update CPU-local rcu_data state to record the beginnings and ends of
|
||
* grace periods. The caller must hold the ->lock of the leaf rcu_node
|
||
* structure corresponding to the current CPU, and must have irqs disabled.
|
||
* Returns true if the grace-period kthread needs to be awakened.
|
||
*/
|
||
static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp)
|
||
{
|
||
bool ret = false;
|
||
bool need_qs;
|
||
const bool offloaded = rcu_rdp_is_offloaded(rdp);
|
||
|
||
raw_lockdep_assert_held_rcu_node(rnp);
|
||
|
||
if (rdp->gp_seq == rnp->gp_seq)
|
||
return false; /* Nothing to do. */
|
||
|
||
/* Handle the ends of any preceding grace periods first. */
|
||
if (rcu_seq_completed_gp(rdp->gp_seq, rnp->gp_seq) ||
|
||
unlikely(READ_ONCE(rdp->gpwrap))) {
|
||
if (!offloaded)
|
||
ret = rcu_advance_cbs(rnp, rdp); /* Advance CBs. */
|
||
rdp->core_needs_qs = false;
|
||
trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuend"));
|
||
} else {
|
||
if (!offloaded)
|
||
ret = rcu_accelerate_cbs(rnp, rdp); /* Recent CBs. */
|
||
if (rdp->core_needs_qs)
|
||
rdp->core_needs_qs = !!(rnp->qsmask & rdp->grpmask);
|
||
}
|
||
|
||
/* Now handle the beginnings of any new-to-this-CPU grace periods. */
|
||
if (rcu_seq_new_gp(rdp->gp_seq, rnp->gp_seq) ||
|
||
unlikely(READ_ONCE(rdp->gpwrap))) {
|
||
/*
|
||
* If the current grace period is waiting for this CPU,
|
||
* set up to detect a quiescent state, otherwise don't
|
||
* go looking for one.
|
||
*/
|
||
trace_rcu_grace_period(rcu_state.name, rnp->gp_seq, TPS("cpustart"));
|
||
need_qs = !!(rnp->qsmask & rdp->grpmask);
|
||
rdp->cpu_no_qs.b.norm = need_qs;
|
||
rdp->core_needs_qs = need_qs;
|
||
zero_cpu_stall_ticks(rdp);
|
||
}
|
||
rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */
|
||
if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap)
|
||
WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);
|
||
if (IS_ENABLED(CONFIG_PROVE_RCU) && READ_ONCE(rdp->gpwrap))
|
||
WRITE_ONCE(rdp->last_sched_clock, jiffies);
|
||
WRITE_ONCE(rdp->gpwrap, false);
|
||
rcu_gpnum_ovf(rnp, rdp);
|
||
return ret;
|
||
}
|
||
|
||
static void note_gp_changes(struct rcu_data *rdp)
|
||
{
|
||
unsigned long flags;
|
||
bool needwake;
|
||
struct rcu_node *rnp;
|
||
|
||
local_irq_save(flags);
|
||
rnp = rdp->mynode;
|
||
if ((rdp->gp_seq == rcu_seq_current(&rnp->gp_seq) &&
|
||
!unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
|
||
!raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */
|
||
local_irq_restore(flags);
|
||
return;
|
||
}
|
||
needwake = __note_gp_changes(rnp, rdp);
|
||
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
||
rcu_strict_gp_check_qs();
|
||
if (needwake)
|
||
rcu_gp_kthread_wake();
|
||
}
|
||
|
||
static atomic_t *rcu_gp_slow_suppress;
|
||
|
||
/* Register a counter to suppress debugging grace-period delays. */
|
||
void rcu_gp_slow_register(atomic_t *rgssp)
|
||
{
|
||
WARN_ON_ONCE(rcu_gp_slow_suppress);
|
||
|
||
WRITE_ONCE(rcu_gp_slow_suppress, rgssp);
|
||
}
|
||
EXPORT_SYMBOL_GPL(rcu_gp_slow_register);
|
||
|
||
/* Unregister a counter, with NULL for not caring which. */
|
||
void rcu_gp_slow_unregister(atomic_t *rgssp)
|
||
{
|
||
WARN_ON_ONCE(rgssp && rgssp != rcu_gp_slow_suppress && rcu_gp_slow_suppress != NULL);
|
||
|
||
WRITE_ONCE(rcu_gp_slow_suppress, NULL);
|
||
}
|
||
EXPORT_SYMBOL_GPL(rcu_gp_slow_unregister);
|
||
|
||
static bool rcu_gp_slow_is_suppressed(void)
|
||
{
|
||
atomic_t *rgssp = READ_ONCE(rcu_gp_slow_suppress);
|
||
|
||
return rgssp && atomic_read(rgssp);
|
||
}
|
||
|
||
static void rcu_gp_slow(int delay)
|
||
{
|
||
if (!rcu_gp_slow_is_suppressed() && delay > 0 &&
|
||
!(rcu_seq_ctr(rcu_state.gp_seq) % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
|
||
schedule_timeout_idle(delay);
|
||
}
|
||
|
||
static unsigned long sleep_duration;
|
||
|
||
/* Allow rcutorture to stall the grace-period kthread. */
|
||
void rcu_gp_set_torture_wait(int duration)
|
||
{
|
||
if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST) && duration > 0)
|
||
WRITE_ONCE(sleep_duration, duration);
|
||
}
|
||
EXPORT_SYMBOL_GPL(rcu_gp_set_torture_wait);
|
||
|
||
/* Actually implement the aforementioned wait. */
|
||
static void rcu_gp_torture_wait(void)
|
||
{
|
||
unsigned long duration;
|
||
|
||
if (!IS_ENABLED(CONFIG_RCU_TORTURE_TEST))
|
||
return;
|
||
duration = xchg(&sleep_duration, 0UL);
|
||
if (duration > 0) {
|
||
pr_alert("%s: Waiting %lu jiffies\n", __func__, duration);
|
||
schedule_timeout_idle(duration);
|
||
pr_alert("%s: Wait complete\n", __func__);
|
||
}
|
||
}
|
||
|
||
/*
|
||
* Handler for on_each_cpu() to invoke the target CPU's RCU core
|
||
* processing.
|
||
*/
|
||
static void rcu_strict_gp_boundary(void *unused)
|
||
{
|
||
invoke_rcu_core();
|
||
}
|
||
|
||
// Make the polled API aware of the beginning of a grace period.
|
||
static void rcu_poll_gp_seq_start(unsigned long *snap)
|
||
{
|
||
struct rcu_node *rnp = rcu_get_root();
|
||
|
||
if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
|
||
raw_lockdep_assert_held_rcu_node(rnp);
|
||
|
||
// If RCU was idle, note beginning of GP.
|
||
if (!rcu_seq_state(rcu_state.gp_seq_polled))
|
||
rcu_seq_start(&rcu_state.gp_seq_polled);
|
||
|
||
// Either way, record current state.
|
||
*snap = rcu_state.gp_seq_polled;
|
||
}
|
||
|
||
// Make the polled API aware of the end of a grace period.
|
||
static void rcu_poll_gp_seq_end(unsigned long *snap)
|
||
{
|
||
struct rcu_node *rnp = rcu_get_root();
|
||
|
||
if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
|
||
raw_lockdep_assert_held_rcu_node(rnp);
|
||
|
||
// If the previously noted GP is still in effect, record the
|
||
// end of that GP. Either way, zero counter to avoid counter-wrap
|
||
// problems.
|
||
if (*snap && *snap == rcu_state.gp_seq_polled) {
|
||
rcu_seq_end(&rcu_state.gp_seq_polled);
|
||
rcu_state.gp_seq_polled_snap = 0;
|
||
rcu_state.gp_seq_polled_exp_snap = 0;
|
||
} else {
|
||
*snap = 0;
|
||
}
|
||
}
|
||
|
||
// Make the polled API aware of the beginning of a grace period, but
|
||
// where caller does not hold the root rcu_node structure's lock.
|
||
static void rcu_poll_gp_seq_start_unlocked(unsigned long *snap)
|
||
{
|
||
unsigned long flags;
|
||
struct rcu_node *rnp = rcu_get_root();
|
||
|
||
if (rcu_init_invoked()) {
|
||
if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
|
||
lockdep_assert_irqs_enabled();
|
||
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
||
}
|
||
rcu_poll_gp_seq_start(snap);
|
||
if (rcu_init_invoked())
|
||
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
||
}
|
||
|
||
// Make the polled API aware of the end of a grace period, but where
|
||
// caller does not hold the root rcu_node structure's lock.
|
||
static void rcu_poll_gp_seq_end_unlocked(unsigned long *snap)
|
||
{
|
||
unsigned long flags;
|
||
struct rcu_node *rnp = rcu_get_root();
|
||
|
||
if (rcu_init_invoked()) {
|
||
if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
|
||
lockdep_assert_irqs_enabled();
|
||
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
||
}
|
||
rcu_poll_gp_seq_end(snap);
|
||
if (rcu_init_invoked())
|
||
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
||
}
|
||
|
||
/*
|
||
* There is a single llist, which is used for handling
|
||
* synchronize_rcu() users' enqueued rcu_synchronize nodes.
|
||
* Within this llist, there are two tail pointers:
|
||
*
|
||
* wait tail: Tracks the set of nodes, which need to
|
||
* wait for the current GP to complete.
|
||
* done tail: Tracks the set of nodes, for which grace
|
||
* period has elapsed. These nodes processing
|
||
* will be done as part of the cleanup work
|
||
* execution by a kworker.
|
||
*
|
||
* At every grace period init, a new wait node is added
|
||
* to the llist. This wait node is used as wait tail
|
||
* for this new grace period. Given that there are a fixed
|
||
* number of wait nodes, if all wait nodes are in use
|
||
* (which can happen when kworker callback processing
|
||
* is delayed) and additional grace period is requested.
|
||
* This means, a system is slow in processing callbacks.
|
||
*
|
||
* TODO: If a slow processing is detected, a first node
|
||
* in the llist should be used as a wait-tail for this
|
||
* grace period, therefore users which should wait due
|
||
* to a slow process are handled by _this_ grace period
|
||
* and not next.
|
||
*
|
||
* Below is an illustration of how the done and wait
|
||
* tail pointers move from one set of rcu_synchronize nodes
|
||
* to the other, as grace periods start and finish and
|
||
* nodes are processed by kworker.
|
||
*
|
||
*
|
||
* a. Initial llist callbacks list:
|
||
*
|
||
* +----------+ +--------+ +-------+
|
||
* | | | | | |
|
||
* | head |---------> | cb2 |--------->| cb1 |
|
||
* | | | | | |
|
||
* +----------+ +--------+ +-------+
|
||
*
|
||
*
|
||
*
|
||
* b. New GP1 Start:
|
||
*
|
||
* WAIT TAIL
|
||
* |
|
||
* |
|
||
* v
|
||
* +----------+ +--------+ +--------+ +-------+
|
||
* | | | | | | | |
|
||
* | head ------> wait |------> cb2 |------> | cb1 |
|
||
* | | | head1 | | | | |
|
||
* +----------+ +--------+ +--------+ +-------+
|
||
*
|
||
*
|
||
*
|
||
* c. GP completion:
|
||
*
|
||
* WAIT_TAIL == DONE_TAIL
|
||
*
|
||
* DONE TAIL
|
||
* |
|
||
* |
|
||
* v
|
||
* +----------+ +--------+ +--------+ +-------+
|
||
* | | | | | | | |
|
||
* | head ------> wait |------> cb2 |------> | cb1 |
|
||
* | | | head1 | | | | |
|
||
* +----------+ +--------+ +--------+ +-------+
|
||
*
|
||
*
|
||
*
|
||
* d. New callbacks and GP2 start:
|
||
*
|
||
* WAIT TAIL DONE TAIL
|
||
* | |
|
||
* | |
|
||
* v v
|
||
* +----------+ +------+ +------+ +------+ +-----+ +-----+ +-----+
|
||
* | | | | | | | | | | | | | |
|
||
* | head ------> wait |--->| cb4 |--->| cb3 |--->|wait |--->| cb2 |--->| cb1 |
|
||
* | | | head2| | | | | |head1| | | | |
|
||
* +----------+ +------+ +------+ +------+ +-----+ +-----+ +-----+
|
||
*
|
||
*
|
||
*
|
||
* e. GP2 completion:
|
||
*
|
||
* WAIT_TAIL == DONE_TAIL
|
||
* DONE TAIL
|
||
* |
|
||
* |
|
||
* v
|
||
* +----------+ +------+ +------+ +------+ +-----+ +-----+ +-----+
|
||
* | | | | | | | | | | | | | |
|
||
* | head ------> wait |--->| cb4 |--->| cb3 |--->|wait |--->| cb2 |--->| cb1 |
|
||
* | | | head2| | | | | |head1| | | | |
|
||
* +----------+ +------+ +------+ +------+ +-----+ +-----+ +-----+
|
||
*
|
||
*
|
||
* While the llist state transitions from d to e, a kworker
|
||
* can start executing rcu_sr_normal_gp_cleanup_work() and
|
||
* can observe either the old done tail (@c) or the new
|
||
* done tail (@e). So, done tail updates and reads need
|
||
* to use the rel-acq semantics. If the concurrent kworker
|
||
* observes the old done tail, the newly queued work
|
||
* execution will process the updated done tail. If the
|
||
* concurrent kworker observes the new done tail, then
|
||
* the newly queued work will skip processing the done
|
||
* tail, as workqueue semantics guarantees that the new
|
||
* work is executed only after the previous one completes.
|
||
*
|
||
* f. kworker callbacks processing complete:
|
||
*
|
||
*
|
||
* DONE TAIL
|
||
* |
|
||
* |
|
||
* v
|
||
* +----------+ +--------+
|
||
* | | | |
|
||
* | head ------> wait |
|
||
* | | | head2 |
|
||
* +----------+ +--------+
|
||
*
|
||
*/
|
||
static bool rcu_sr_is_wait_head(struct llist_node *node)
|
||
{
|
||
return &(rcu_state.srs_wait_nodes)[0].node <= node &&
|
||
node <= &(rcu_state.srs_wait_nodes)[SR_NORMAL_GP_WAIT_HEAD_MAX - 1].node;
|
||
}
|
||
|
||
static struct llist_node *rcu_sr_get_wait_head(void)
|
||
{
|
||
struct sr_wait_node *sr_wn;
|
||
int i;
|
||
|
||
for (i = 0; i < SR_NORMAL_GP_WAIT_HEAD_MAX; i++) {
|
||
sr_wn = &(rcu_state.srs_wait_nodes)[i];
|
||
|
||
if (!atomic_cmpxchg_acquire(&sr_wn->inuse, 0, 1))
|
||
return &sr_wn->node;
|
||
}
|
||
|
||
return NULL;
|
||
}
|
||
|
||
static void rcu_sr_put_wait_head(struct llist_node *node)
|
||
{
|
||
struct sr_wait_node *sr_wn = container_of(node, struct sr_wait_node, node);
|
||
|
||
atomic_set_release(&sr_wn->inuse, 0);
|
||
}
|
||
|
||
/* Disabled by default. */
|
||
static int rcu_normal_wake_from_gp;
|
||
module_param(rcu_normal_wake_from_gp, int, 0644);
|
||
static struct workqueue_struct *sync_wq;
|
||
|
||
static void rcu_sr_normal_complete(struct llist_node *node)
|
||
{
|
||
struct rcu_synchronize *rs = container_of(
|
||
(struct rcu_head *) node, struct rcu_synchronize, head);
|
||
unsigned long oldstate = (unsigned long) rs->head.func;
|
||
|
||
WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) &&
|
||
!poll_state_synchronize_rcu(oldstate),
|
||
"A full grace period is not passed yet: %lu",
|
||
rcu_seq_diff(get_state_synchronize_rcu(), oldstate));
|
||
|
||
/* Finally. */
|
||
complete(&rs->completion);
|
||
}
|
||
|
||
static void rcu_sr_normal_gp_cleanup_work(struct work_struct *work)
|
||
{
|
||
struct llist_node *done, *rcu, *next, *head;
|
||
|
||
/*
|
||
* This work execution can potentially execute
|
||
* while a new done tail is being updated by
|
||
* grace period kthread in rcu_sr_normal_gp_cleanup().
|
||
* So, read and updates of done tail need to
|
||
* follow acq-rel semantics.
|
||
*
|
||
* Given that wq semantics guarantees that a single work
|
||
* cannot execute concurrently by multiple kworkers,
|
||
* the done tail list manipulations are protected here.
|
||
*/
|
||
done = smp_load_acquire(&rcu_state.srs_done_tail);
|
||
if (WARN_ON_ONCE(!done))
|
||
return;
|
||
|
||
WARN_ON_ONCE(!rcu_sr_is_wait_head(done));
|
||
head = done->next;
|
||
done->next = NULL;
|
||
|
||
/*
|
||
* The dummy node, which is pointed to by the
|
||
* done tail which is acq-read above is not removed
|
||
* here. This allows lockless additions of new
|
||
* rcu_synchronize nodes in rcu_sr_normal_add_req(),
|
||
* while the cleanup work executes. The dummy
|
||
* nodes is removed, in next round of cleanup
|
||
* work execution.
|
||
*/
|
||
llist_for_each_safe(rcu, next, head) {
|
||
if (!rcu_sr_is_wait_head(rcu)) {
|
||
rcu_sr_normal_complete(rcu);
|
||
continue;
|
||
}
|
||
|
||
rcu_sr_put_wait_head(rcu);
|
||
}
|
||
|
||
/* Order list manipulations with atomic access. */
|
||
atomic_dec_return_release(&rcu_state.srs_cleanups_pending);
|
||
}
|
||
|
||
/*
|
||
* Helper function for rcu_gp_cleanup().
|
||
*/
|
||
static void rcu_sr_normal_gp_cleanup(void)
|
||
{
|
||
struct llist_node *wait_tail, *next = NULL, *rcu = NULL;
|
||
int done = 0;
|
||
|
||
wait_tail = rcu_state.srs_wait_tail;
|
||
if (wait_tail == NULL)
|
||
return;
|
||
|
||
rcu_state.srs_wait_tail = NULL;
|
||
ASSERT_EXCLUSIVE_WRITER(rcu_state.srs_wait_tail);
|
||
WARN_ON_ONCE(!rcu_sr_is_wait_head(wait_tail));
|
||
|
||
/*
|
||
* Process (a) and (d) cases. See an illustration.
|
||
*/
|
||
llist_for_each_safe(rcu, next, wait_tail->next) {
|
||
if (rcu_sr_is_wait_head(rcu))
|
||
break;
|
||
|
||
rcu_sr_normal_complete(rcu);
|
||
// It can be last, update a next on this step.
|
||
wait_tail->next = next;
|
||
|
||
if (++done == SR_MAX_USERS_WAKE_FROM_GP)
|
||
break;
|
||
}
|
||
|
||
/*
|
||
* Fast path, no more users to process except putting the second last
|
||
* wait head if no inflight-workers. If there are in-flight workers,
|
||
* they will remove the last wait head.
|
||
*
|
||
* Note that the ACQUIRE orders atomic access with list manipulation.
|
||
*/
|
||
if (wait_tail->next && wait_tail->next->next == NULL &&
|
||
rcu_sr_is_wait_head(wait_tail->next) &&
|
||
!atomic_read_acquire(&rcu_state.srs_cleanups_pending)) {
|
||
rcu_sr_put_wait_head(wait_tail->next);
|
||
wait_tail->next = NULL;
|
||
}
|
||
|
||
/* Concurrent sr_normal_gp_cleanup work might observe this update. */
|
||
ASSERT_EXCLUSIVE_WRITER(rcu_state.srs_done_tail);
|
||
smp_store_release(&rcu_state.srs_done_tail, wait_tail);
|
||
|
||
/*
|
||
* We schedule a work in order to perform a final processing
|
||
* of outstanding users(if still left) and releasing wait-heads
|
||
* added by rcu_sr_normal_gp_init() call.
|
||
*/
|
||
if (wait_tail->next) {
|
||
atomic_inc(&rcu_state.srs_cleanups_pending);
|
||
if (!queue_work(sync_wq, &rcu_state.srs_cleanup_work))
|
||
atomic_dec(&rcu_state.srs_cleanups_pending);
|
||
}
|
||
}
|
||
|
||
/*
|
||
* Helper function for rcu_gp_init().
|
||
*/
|
||
static bool rcu_sr_normal_gp_init(void)
|
||
{
|
||
struct llist_node *first;
|
||
struct llist_node *wait_head;
|
||
bool start_new_poll = false;
|
||
|
||
first = READ_ONCE(rcu_state.srs_next.first);
|
||
if (!first || rcu_sr_is_wait_head(first))
|
||
return start_new_poll;
|
||
|
||
wait_head = rcu_sr_get_wait_head();
|
||
if (!wait_head) {
|
||
// Kick another GP to retry.
|
||
start_new_poll = true;
|
||
return start_new_poll;
|
||
}
|
||
|
||
/* Inject a wait-dummy-node. */
|
||
llist_add(wait_head, &rcu_state.srs_next);
|
||
|
||
/*
|
||
* A waiting list of rcu_synchronize nodes should be empty on
|
||
* this step, since a GP-kthread, rcu_gp_init() -> gp_cleanup(),
|
||
* rolls it over. If not, it is a BUG, warn a user.
|
||
*/
|
||
WARN_ON_ONCE(rcu_state.srs_wait_tail != NULL);
|
||
rcu_state.srs_wait_tail = wait_head;
|
||
ASSERT_EXCLUSIVE_WRITER(rcu_state.srs_wait_tail);
|
||
|
||
return start_new_poll;
|
||
}
|
||
|
||
static void rcu_sr_normal_add_req(struct rcu_synchronize *rs)
|
||
{
|
||
llist_add((struct llist_node *) &rs->head, &rcu_state.srs_next);
|
||
}
|
||
|
||
/*
|
||
* Initialize a new grace period. Return false if no grace period required.
|
||
*/
|
||
static noinline_for_stack bool rcu_gp_init(void)
|
||
{
|
||
unsigned long flags;
|
||
unsigned long oldmask;
|
||
unsigned long mask;
|
||
struct rcu_data *rdp;
|
||
struct rcu_node *rnp = rcu_get_root();
|
||
bool start_new_poll;
|
||
|
||
WRITE_ONCE(rcu_state.gp_activity, jiffies);
|
||
raw_spin_lock_irq_rcu_node(rnp);
|
||
if (!rcu_state.gp_flags) {
|
||
/* Spurious wakeup, tell caller to go back to sleep. */
|
||
raw_spin_unlock_irq_rcu_node(rnp);
|
||
return false;
|
||
}
|
||
WRITE_ONCE(rcu_state.gp_flags, 0); /* Clear all flags: New GP. */
|
||
|
||
if (WARN_ON_ONCE(rcu_gp_in_progress())) {
|
||
/*
|
||
* Grace period already in progress, don't start another.
|
||
* Not supposed to be able to happen.
|
||
*/
|
||
raw_spin_unlock_irq_rcu_node(rnp);
|
||
return false;
|
||
}
|
||
|
||
/* Advance to a new grace period and initialize state. */
|
||
record_gp_stall_check_time();
|
||
/* Record GP times before starting GP, hence rcu_seq_start(). */
|
||
rcu_seq_start(&rcu_state.gp_seq);
|
||
ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
|
||
start_new_poll = rcu_sr_normal_gp_init();
|
||
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("start"));
|
||
rcu_poll_gp_seq_start(&rcu_state.gp_seq_polled_snap);
|
||
raw_spin_unlock_irq_rcu_node(rnp);
|
||
|
||
/*
|
||
* The "start_new_poll" is set to true, only when this GP is not able
|
||
* to handle anything and there are outstanding users. It happens when
|
||
* the rcu_sr_normal_gp_init() function was not able to insert a dummy
|
||
* separator to the llist, because there were no left any dummy-nodes.
|
||
*
|
||
* Number of dummy-nodes is fixed, it could be that we are run out of
|
||
* them, if so we start a new pool request to repeat a try. It is rare
|
||
* and it means that a system is doing a slow processing of callbacks.
|
||
*/
|
||
if (start_new_poll)
|
||
(void) start_poll_synchronize_rcu();
|
||
|
||
/*
|
||
* Apply per-leaf buffered online and offline operations to
|
||
* the rcu_node tree. Note that this new grace period need not
|
||
* wait for subsequent online CPUs, and that RCU hooks in the CPU
|
||
* offlining path, when combined with checks in this function,
|
||
* will handle CPUs that are currently going offline or that will
|
||
* go offline later. Please also refer to "Hotplug CPU" section
|
||
* of RCU's Requirements documentation.
|
||
*/
|
||
WRITE_ONCE(rcu_state.gp_state, RCU_GP_ONOFF);
|
||
/* Exclude CPU hotplug operations. */
|
||
rcu_for_each_leaf_node(rnp) {
|
||
local_irq_disable();
|
||
arch_spin_lock(&rcu_state.ofl_lock);
|
||
raw_spin_lock_rcu_node(rnp);
|
||
if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
|
||
!rnp->wait_blkd_tasks) {
|
||
/* Nothing to do on this leaf rcu_node structure. */
|
||
raw_spin_unlock_rcu_node(rnp);
|
||
arch_spin_unlock(&rcu_state.ofl_lock);
|
||
local_irq_enable();
|
||
continue;
|
||
}
|
||
|
||
/* Record old state, apply changes to ->qsmaskinit field. */
|
||
oldmask = rnp->qsmaskinit;
|
||
rnp->qsmaskinit = rnp->qsmaskinitnext;
|
||
|
||
/* If zero-ness of ->qsmaskinit changed, propagate up tree. */
|
||
if (!oldmask != !rnp->qsmaskinit) {
|
||
if (!oldmask) { /* First online CPU for rcu_node. */
|
||
if (!rnp->wait_blkd_tasks) /* Ever offline? */
|
||
rcu_init_new_rnp(rnp);
|
||
} else if (rcu_preempt_has_tasks(rnp)) {
|
||
rnp->wait_blkd_tasks = true; /* blocked tasks */
|
||
} else { /* Last offline CPU and can propagate. */
|
||
rcu_cleanup_dead_rnp(rnp);
|
||
}
|
||
}
|
||
|
||
/*
|
||
* If all waited-on tasks from prior grace period are
|
||
* done, and if all this rcu_node structure's CPUs are
|
||
* still offline, propagate up the rcu_node tree and
|
||
* clear ->wait_blkd_tasks. Otherwise, if one of this
|
||
* rcu_node structure's CPUs has since come back online,
|
||
* simply clear ->wait_blkd_tasks.
|
||
*/
|
||
if (rnp->wait_blkd_tasks &&
|
||
(!rcu_preempt_has_tasks(rnp) || rnp->qsmaskinit)) {
|
||
rnp->wait_blkd_tasks = false;
|
||
if (!rnp->qsmaskinit)
|
||
rcu_cleanup_dead_rnp(rnp);
|
||
}
|
||
|
||
raw_spin_unlock_rcu_node(rnp);
|
||
arch_spin_unlock(&rcu_state.ofl_lock);
|
||
local_irq_enable();
|
||
}
|
||
rcu_gp_slow(gp_preinit_delay); /* Races with CPU hotplug. */
|
||
|
||
/*
|
||
* Set the quiescent-state-needed bits in all the rcu_node
|
||
* structures for all currently online CPUs in breadth-first
|
||
* order, starting from the root rcu_node structure, relying on the
|
||
* layout of the tree within the rcu_state.node[] array. Note that
|
||
* other CPUs will access only the leaves of the hierarchy, thus
|
||
* seeing that no grace period is in progress, at least until the
|
||
* corresponding leaf node has been initialized.
|
||
*
|
||
* The grace period cannot complete until the initialization
|
||
* process finishes, because this kthread handles both.
|
||
*/
|
||
WRITE_ONCE(rcu_state.gp_state, RCU_GP_INIT);
|
||
rcu_for_each_node_breadth_first(rnp) {
|
||
rcu_gp_slow(gp_init_delay);
|
||
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
||
rdp = this_cpu_ptr(&rcu_data);
|
||
rcu_preempt_check_blocked_tasks(rnp);
|
||
rnp->qsmask = rnp->qsmaskinit;
|
||
WRITE_ONCE(rnp->gp_seq, rcu_state.gp_seq);
|
||
if (rnp == rdp->mynode)
|
||
(void)__note_gp_changes(rnp, rdp);
|
||
rcu_preempt_boost_start_gp(rnp);
|
||
trace_rcu_grace_period_init(rcu_state.name, rnp->gp_seq,
|
||
rnp->level, rnp->grplo,
|
||
rnp->grphi, rnp->qsmask);
|
||
/* Quiescent states for tasks on any now-offline CPUs. */
|
||
mask = rnp->qsmask & ~rnp->qsmaskinitnext;
|
||
rnp->rcu_gp_init_mask = mask;
|
||
if ((mask || rnp->wait_blkd_tasks) && rcu_is_leaf_node(rnp))
|
||
rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
|
||
else
|
||
raw_spin_unlock_irq_rcu_node(rnp);
|
||
cond_resched_tasks_rcu_qs();
|
||
WRITE_ONCE(rcu_state.gp_activity, jiffies);
|
||
}
|
||
|
||
// If strict, make all CPUs aware of new grace period.
|
||
if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
|
||
on_each_cpu(rcu_strict_gp_boundary, NULL, 0);
|
||
|
||
return true;
|
||
}
|
||
|
||
/*
|
||
* Helper function for swait_event_idle_exclusive() wakeup at force-quiescent-state
|
||
* time.
|
||
*/
|
||
static bool rcu_gp_fqs_check_wake(int *gfp)
|
||
{
|
||
struct rcu_node *rnp = rcu_get_root();
|
||
|
||
// If under overload conditions, force an immediate FQS scan.
|
||
if (*gfp & RCU_GP_FLAG_OVLD)
|
||
return true;
|
||
|
||
// Someone like call_rcu() requested a force-quiescent-state scan.
|
||
*gfp = READ_ONCE(rcu_state.gp_flags);
|
||
if (*gfp & RCU_GP_FLAG_FQS)
|
||
return true;
|
||
|
||
// The current grace period has completed.
|
||
if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
|
||
return true;
|
||
|
||
return false;
|
||
}
|
||
|
||
/*
|
||
* Do one round of quiescent-state forcing.
|
||
*/
|
||
static void rcu_gp_fqs(bool first_time)
|
||
{
|
||
int nr_fqs = READ_ONCE(rcu_state.nr_fqs_jiffies_stall);
|
||
struct rcu_node *rnp = rcu_get_root();
|
||
|
||
WRITE_ONCE(rcu_state.gp_activity, jiffies);
|
||
WRITE_ONCE(rcu_state.n_force_qs, rcu_state.n_force_qs + 1);
|
||
|
||
WARN_ON_ONCE(nr_fqs > 3);
|
||
/* Only countdown nr_fqs for stall purposes if jiffies moves. */
|
||
if (nr_fqs) {
|
||
if (nr_fqs == 1) {
|
||
WRITE_ONCE(rcu_state.jiffies_stall,
|
||
jiffies + rcu_jiffies_till_stall_check());
|
||
}
|
||
WRITE_ONCE(rcu_state.nr_fqs_jiffies_stall, --nr_fqs);
|
||
}
|
||
|
||
if (first_time) {
|
||
/* Collect dyntick-idle snapshots. */
|
||
force_qs_rnp(rcu_watching_snap_save);
|
||
} else {
|
||
/* Handle dyntick-idle and offline CPUs. */
|
||
force_qs_rnp(rcu_watching_snap_recheck);
|
||
}
|
||
/* Clear flag to prevent immediate re-entry. */
|
||
if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
|
||
raw_spin_lock_irq_rcu_node(rnp);
|
||
WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags & ~RCU_GP_FLAG_FQS);
|
||
raw_spin_unlock_irq_rcu_node(rnp);
|
||
}
|
||
}
|
||
|
||
/*
|
||
* Loop doing repeated quiescent-state forcing until the grace period ends.
|
||
*/
|
||
static noinline_for_stack void rcu_gp_fqs_loop(void)
|
||
{
|
||
bool first_gp_fqs = true;
|
||
int gf = 0;
|
||
unsigned long j;
|
||
int ret;
|
||
struct rcu_node *rnp = rcu_get_root();
|
||
|
||
j = READ_ONCE(jiffies_till_first_fqs);
|
||
if (rcu_state.cbovld)
|
||
gf = RCU_GP_FLAG_OVLD;
|
||
ret = 0;
|
||
for (;;) {
|
||
if (rcu_state.cbovld) {
|
||
j = (j + 2) / 3;
|
||
if (j <= 0)
|
||
j = 1;
|
||
}
|
||
if (!ret || time_before(jiffies + j, rcu_state.jiffies_force_qs)) {
|
||
WRITE_ONCE(rcu_state.jiffies_force_qs, jiffies + j);
|
||
/*
|
||
* jiffies_force_qs before RCU_GP_WAIT_FQS state
|
||
* update; required for stall checks.
|
||
*/
|
||
smp_wmb();
|
||
WRITE_ONCE(rcu_state.jiffies_kick_kthreads,
|
||
jiffies + (j ? 3 * j : 2));
|
||
}
|
||
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
|
||
TPS("fqswait"));
|
||
WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_FQS);
|
||
(void)swait_event_idle_timeout_exclusive(rcu_state.gp_wq,
|
||
rcu_gp_fqs_check_wake(&gf), j);
|
||
rcu_gp_torture_wait();
|
||
WRITE_ONCE(rcu_state.gp_state, RCU_GP_DOING_FQS);
|
||
/* Locking provides needed memory barriers. */
|
||
/*
|
||
* Exit the loop if the root rcu_node structure indicates that the grace period
|
||
* has ended, leave the loop. The rcu_preempt_blocked_readers_cgp(rnp) check
|
||
* is required only for single-node rcu_node trees because readers blocking
|
||
* the current grace period are queued only on leaf rcu_node structures.
|
||
* For multi-node trees, checking the root node's ->qsmask suffices, because a
|
||
* given root node's ->qsmask bit is cleared only when all CPUs and tasks from
|
||
* the corresponding leaf nodes have passed through their quiescent state.
|
||
*/
|
||
if (!READ_ONCE(rnp->qsmask) &&
|
||
!rcu_preempt_blocked_readers_cgp(rnp))
|
||
break;
|
||
/* If time for quiescent-state forcing, do it. */
|
||
if (!time_after(rcu_state.jiffies_force_qs, jiffies) ||
|
||
(gf & (RCU_GP_FLAG_FQS | RCU_GP_FLAG_OVLD))) {
|
||
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
|
||
TPS("fqsstart"));
|
||
rcu_gp_fqs(first_gp_fqs);
|
||
gf = 0;
|
||
if (first_gp_fqs) {
|
||
first_gp_fqs = false;
|
||
gf = rcu_state.cbovld ? RCU_GP_FLAG_OVLD : 0;
|
||
}
|
||
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
|
||
TPS("fqsend"));
|
||
cond_resched_tasks_rcu_qs();
|
||
WRITE_ONCE(rcu_state.gp_activity, jiffies);
|
||
ret = 0; /* Force full wait till next FQS. */
|
||
j = READ_ONCE(jiffies_till_next_fqs);
|
||
} else {
|
||
/* Deal with stray signal. */
|
||
cond_resched_tasks_rcu_qs();
|
||
WRITE_ONCE(rcu_state.gp_activity, jiffies);
|
||
WARN_ON(signal_pending(current));
|
||
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
|
||
TPS("fqswaitsig"));
|
||
ret = 1; /* Keep old FQS timing. */
|
||
j = jiffies;
|
||
if (time_after(jiffies, rcu_state.jiffies_force_qs))
|
||
j = 1;
|
||
else
|
||
j = rcu_state.jiffies_force_qs - j;
|
||
gf = 0;
|
||
}
|
||
}
|
||
}
|
||
|
||
/*
|
||
* Clean up after the old grace period.
|
||
*/
|
||
static noinline void rcu_gp_cleanup(void)
|
||
{
|
||
int cpu;
|
||
bool needgp = false;
|
||
unsigned long gp_duration;
|
||
unsigned long new_gp_seq;
|
||
bool offloaded;
|
||
struct rcu_data *rdp;
|
||
struct rcu_node *rnp = rcu_get_root();
|
||
struct swait_queue_head *sq;
|
||
|
||
WRITE_ONCE(rcu_state.gp_activity, jiffies);
|
||
raw_spin_lock_irq_rcu_node(rnp);
|
||
rcu_state.gp_end = jiffies;
|
||
gp_duration = rcu_state.gp_end - rcu_state.gp_start;
|
||
if (gp_duration > rcu_state.gp_max)
|
||
rcu_state.gp_max = gp_duration;
|
||
|
||
/*
|
||
* We know the grace period is complete, but to everyone else
|
||
* it appears to still be ongoing. But it is also the case
|
||
* that to everyone else it looks like there is nothing that
|
||
* they can do to advance the grace period. It is therefore
|
||
* safe for us to drop the lock in order to mark the grace
|
||
* period as completed in all of the rcu_node structures.
|
||
*/
|
||
rcu_poll_gp_seq_end(&rcu_state.gp_seq_polled_snap);
|
||
raw_spin_unlock_irq_rcu_node(rnp);
|
||
|
||
/*
|
||
* Propagate new ->gp_seq value to rcu_node structures so that
|
||
* other CPUs don't have to wait until the start of the next grace
|
||
* period to process their callbacks. This also avoids some nasty
|
||
* RCU grace-period initialization races by forcing the end of
|
||
* the current grace period to be completely recorded in all of
|
||
* the rcu_node structures before the beginning of the next grace
|
||
* period is recorded in any of the rcu_node structures.
|
||
*/
|
||
new_gp_seq = rcu_state.gp_seq;
|
||
rcu_seq_end(&new_gp_seq);
|
||
rcu_for_each_node_breadth_first(rnp) {
|
||
raw_spin_lock_irq_rcu_node(rnp);
|
||
if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
|
||
dump_blkd_tasks(rnp, 10);
|
||
WARN_ON_ONCE(rnp->qsmask);
|
||
WRITE_ONCE(rnp->gp_seq, new_gp_seq);
|
||
if (!rnp->parent)
|
||
smp_mb(); // Order against failing poll_state_synchronize_rcu_full().
|
||
rdp = this_cpu_ptr(&rcu_data);
|
||
if (rnp == rdp->mynode)
|
||
needgp = __note_gp_changes(rnp, rdp) || needgp;
|
||
/* smp_mb() provided by prior unlock-lock pair. */
|
||
needgp = rcu_future_gp_cleanup(rnp) || needgp;
|
||
// Reset overload indication for CPUs no longer overloaded
|
||
if (rcu_is_leaf_node(rnp))
|
||
for_each_leaf_node_cpu_mask(rnp, cpu, rnp->cbovldmask) {
|
||
rdp = per_cpu_ptr(&rcu_data, cpu);
|
||
check_cb_ovld_locked(rdp, rnp);
|
||
}
|
||
sq = rcu_nocb_gp_get(rnp);
|
||
raw_spin_unlock_irq_rcu_node(rnp);
|
||
rcu_nocb_gp_cleanup(sq);
|
||
cond_resched_tasks_rcu_qs();
|
||
WRITE_ONCE(rcu_state.gp_activity, jiffies);
|
||
rcu_gp_slow(gp_cleanup_delay);
|
||
}
|
||
rnp = rcu_get_root();
|
||
raw_spin_lock_irq_rcu_node(rnp); /* GP before ->gp_seq update. */
|
||
|
||
/* Declare grace period done, trace first to use old GP number. */
|
||
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("end"));
|
||
rcu_seq_end(&rcu_state.gp_seq);
|
||
ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
|
||
WRITE_ONCE(rcu_state.gp_state, RCU_GP_IDLE);
|
||
/* Check for GP requests since above loop. */
|
||
rdp = this_cpu_ptr(&rcu_data);
|
||
if (!needgp && ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed)) {
|
||
trace_rcu_this_gp(rnp, rdp, rnp->gp_seq_needed,
|
||
TPS("CleanupMore"));
|
||
needgp = true;
|
||
}
|
||
/* Advance CBs to reduce false positives below. */
|
||
offloaded = rcu_rdp_is_offloaded(rdp);
|
||
if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) {
|
||
|
||
// We get here if a grace period was needed (“needgp”)
|
||
// and the above call to rcu_accelerate_cbs() did not set
|
||
// the RCU_GP_FLAG_INIT bit in ->gp_state (which records
|
||
// the need for another grace period). The purpose
|
||
// of the “offloaded” check is to avoid invoking
|
||
// rcu_accelerate_cbs() on an offloaded CPU because we do not
|
||
// hold the ->nocb_lock needed to safely access an offloaded
|
||
// ->cblist. We do not want to acquire that lock because
|
||
// it can be heavily contended during callback floods.
|
||
|
||
WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT);
|
||
WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
|
||
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("newreq"));
|
||
} else {
|
||
|
||
// We get here either if there is no need for an
|
||
// additional grace period or if rcu_accelerate_cbs() has
|
||
// already set the RCU_GP_FLAG_INIT bit in ->gp_flags.
|
||
// So all we need to do is to clear all of the other
|
||
// ->gp_flags bits.
|
||
|
||
WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags & RCU_GP_FLAG_INIT);
|
||
}
|
||
raw_spin_unlock_irq_rcu_node(rnp);
|
||
|
||
// Make synchronize_rcu() users aware of the end of old grace period.
|
||
rcu_sr_normal_gp_cleanup();
|
||
|
||
// If strict, make all CPUs aware of the end of the old grace period.
|
||
if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
|
||
on_each_cpu(rcu_strict_gp_boundary, NULL, 0);
|
||
}
|
||
|
||
/*
|
||
* Body of kthread that handles grace periods.
|
||
*/
|
||
static int __noreturn rcu_gp_kthread(void *unused)
|
||
{
|
||
rcu_bind_gp_kthread();
|
||
for (;;) {
|
||
|
||
/* Handle grace-period start. */
|
||
for (;;) {
|
||
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
|
||
TPS("reqwait"));
|
||
WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_GPS);
|
||
swait_event_idle_exclusive(rcu_state.gp_wq,
|
||
READ_ONCE(rcu_state.gp_flags) &
|
||
RCU_GP_FLAG_INIT);
|
||
rcu_gp_torture_wait();
|
||
WRITE_ONCE(rcu_state.gp_state, RCU_GP_DONE_GPS);
|
||
/* Locking provides needed memory barrier. */
|
||
if (rcu_gp_init())
|
||
break;
|
||
cond_resched_tasks_rcu_qs();
|
||
WRITE_ONCE(rcu_state.gp_activity, jiffies);
|
||
WARN_ON(signal_pending(current));
|
||
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
|
||
TPS("reqwaitsig"));
|
||
}
|
||
|
||
/* Handle quiescent-state forcing. */
|
||
rcu_gp_fqs_loop();
|
||
|
||
/* Handle grace-period end. */
|
||
WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANUP);
|
||
rcu_gp_cleanup();
|
||
WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANED);
|
||
}
|
||
}
|
||
|
||
/*
|
||
* Report a full set of quiescent states to the rcu_state data structure.
|
||
* Invoke rcu_gp_kthread_wake() to awaken the grace-period kthread if
|
||
* another grace period is required. Whether we wake the grace-period
|
||
* kthread or it awakens itself for the next round of quiescent-state
|
||
* forcing, that kthread will clean up after the just-completed grace
|
||
* period. Note that the caller must hold rnp->lock, which is released
|
||
* before return.
|
||
*/
|
||
static void rcu_report_qs_rsp(unsigned long flags)
|
||
__releases(rcu_get_root()->lock)
|
||
{
|
||
raw_lockdep_assert_held_rcu_node(rcu_get_root());
|
||
WARN_ON_ONCE(!rcu_gp_in_progress());
|
||
WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_FQS);
|
||
raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(), flags);
|
||
rcu_gp_kthread_wake();
|
||
}
|
||
|
||
/*
|
||
* Similar to rcu_report_qs_rdp(), for which it is a helper function.
|
||
* Allows quiescent states for a group of CPUs to be reported at one go
|
||
* to the specified rcu_node structure, though all the CPUs in the group
|
||
* must be represented by the same rcu_node structure (which need not be a
|
||
* leaf rcu_node structure, though it often will be). The gps parameter
|
||
* is the grace-period snapshot, which means that the quiescent states
|
||
* are valid only if rnp->gp_seq is equal to gps. That structure's lock
|
||
* must be held upon entry, and it is released before return.
|
||
*
|
||
* As a special case, if mask is zero, the bit-already-cleared check is
|
||
* disabled. This allows propagating quiescent state due to resumed tasks
|
||
* during grace-period initialization.
|
||
*/
|
||
static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
|
||
unsigned long gps, unsigned long flags)
|
||
__releases(rnp->lock)
|
||
{
|
||
unsigned long oldmask = 0;
|
||
struct rcu_node *rnp_c;
|
||
|
||
raw_lockdep_assert_held_rcu_node(rnp);
|
||
|
||
/* Walk up the rcu_node hierarchy. */
|
||
for (;;) {
|
||
if ((!(rnp->qsmask & mask) && mask) || rnp->gp_seq != gps) {
|
||
|
||
/*
|
||
* Our bit has already been cleared, or the
|
||
* relevant grace period is already over, so done.
|
||
*/
|
||
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
||
return;
|
||
}
|
||
WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
|
||
WARN_ON_ONCE(!rcu_is_leaf_node(rnp) &&
|
||
rcu_preempt_blocked_readers_cgp(rnp));
|
||
WRITE_ONCE(rnp->qsmask, rnp->qsmask & ~mask);
|
||
trace_rcu_quiescent_state_report(rcu_state.name, rnp->gp_seq,
|
||
mask, rnp->qsmask, rnp->level,
|
||
rnp->grplo, rnp->grphi,
|
||
!!rnp->gp_tasks);
|
||
if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
|
||
|
||
/* Other bits still set at this level, so done. */
|
||
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
||
return;
|
||
}
|
||
rnp->completedqs = rnp->gp_seq;
|
||
mask = rnp->grpmask;
|
||
if (rnp->parent == NULL) {
|
||
|
||
/* No more levels. Exit loop holding root lock. */
|
||
|
||
break;
|
||
}
|
||
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
||
rnp_c = rnp;
|
||
rnp = rnp->parent;
|
||
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
||
oldmask = READ_ONCE(rnp_c->qsmask);
|
||
}
|
||
|
||
/*
|
||
* Get here if we are the last CPU to pass through a quiescent
|
||
* state for this grace period. Invoke rcu_report_qs_rsp()
|
||
* to clean up and start the next grace period if one is needed.
|
||
*/
|
||
rcu_report_qs_rsp(flags); /* releases rnp->lock. */
|
||
}
|
||
|
||
/*
|
||
* Record a quiescent state for all tasks that were previously queued
|
||
* on the specified rcu_node structure and that were blocking the current
|
||
* RCU grace period. The caller must hold the corresponding rnp->lock with
|
||
* irqs disabled, and this lock is released upon return, but irqs remain
|
||
* disabled.
|
||
*/
|
||
static void __maybe_unused
|
||
rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
|
||
__releases(rnp->lock)
|
||
{
|
||
unsigned long gps;
|
||
unsigned long mask;
|
||
struct rcu_node *rnp_p;
|
||
|
||
raw_lockdep_assert_held_rcu_node(rnp);
|
||
if (WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT_RCU)) ||
|
||
WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)) ||
|
||
rnp->qsmask != 0) {
|
||
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
||
return; /* Still need more quiescent states! */
|
||
}
|
||
|
||
rnp->completedqs = rnp->gp_seq;
|
||
rnp_p = rnp->parent;
|
||
if (rnp_p == NULL) {
|
||
/*
|
||
* Only one rcu_node structure in the tree, so don't
|
||
* try to report up to its nonexistent parent!
|
||
*/
|
||
rcu_report_qs_rsp(flags);
|
||
return;
|
||
}
|
||
|
||
/* Report up the rest of the hierarchy, tracking current ->gp_seq. */
|
||
gps = rnp->gp_seq;
|
||
mask = rnp->grpmask;
|
||
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
|
||
raw_spin_lock_rcu_node(rnp_p); /* irqs already disabled. */
|
||
rcu_report_qs_rnp(mask, rnp_p, gps, flags);
|
||
}
|
||
|
||
/*
|
||
* Record a quiescent state for the specified CPU to that CPU's rcu_data
|
||
* structure. This must be called from the specified CPU.
|
||
*/
|
||
static void
|
||
rcu_report_qs_rdp(struct rcu_data *rdp)
|
||
{
|
||
unsigned long flags;
|
||
unsigned long mask;
|
||
struct rcu_node *rnp;
|
||
|
||
WARN_ON_ONCE(rdp->cpu != smp_processor_id());
|
||
rnp = rdp->mynode;
|
||
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
||
if (rdp->cpu_no_qs.b.norm || rdp->gp_seq != rnp->gp_seq ||
|
||
rdp->gpwrap) {
|
||
|
||
/*
|
||
* The grace period in which this quiescent state was
|
||
* recorded has ended, so don't report it upwards.
|
||
* We will instead need a new quiescent state that lies
|
||
* within the current grace period.
|
||
*/
|
||
rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */
|
||
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
||
return;
|
||
}
|
||
mask = rdp->grpmask;
|
||
rdp->core_needs_qs = false;
|
||
if ((rnp->qsmask & mask) == 0) {
|
||
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
||
} else {
|
||
/*
|
||
* This GP can't end until cpu checks in, so all of our
|
||
* callbacks can be processed during the next GP.
|
||
*
|
||
* NOCB kthreads have their own way to deal with that...
|
||
*/
|
||
if (!rcu_rdp_is_offloaded(rdp)) {
|
||
/*
|
||
* The current GP has not yet ended, so it
|
||
* should not be possible for rcu_accelerate_cbs()
|
||
* to return true. So complain, but don't awaken.
|
||
*/
|
||
WARN_ON_ONCE(rcu_accelerate_cbs(rnp, rdp));
|
||
}
|
||
|
||
rcu_disable_urgency_upon_qs(rdp);
|
||
rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
|
||
/* ^^^ Released rnp->lock */
|
||
}
|
||
}
|
||
|
||
/*
|
||
* Check to see if there is a new grace period of which this CPU
|
||
* is not yet aware, and if so, set up local rcu_data state for it.
|
||
* Otherwise, see if this CPU has just passed through its first
|
||
* quiescent state for this grace period, and record that fact if so.
|
||
*/
|
||
static void
|
||
rcu_check_quiescent_state(struct rcu_data *rdp)
|
||
{
|
||
/* Check for grace-period ends and beginnings. */
|
||
note_gp_changes(rdp);
|
||
|
||
/*
|
||
* Does this CPU still need to do its part for current grace period?
|
||
* If no, return and let the other CPUs do their part as well.
|
||
*/
|
||
if (!rdp->core_needs_qs)
|
||
return;
|
||
|
||
/*
|
||
* Was there a quiescent state since the beginning of the grace
|
||
* period? If no, then exit and wait for the next call.
|
||
*/
|
||
if (rdp->cpu_no_qs.b.norm)
|
||
return;
|
||
|
||
/*
|
||
* Tell RCU we are done (but rcu_report_qs_rdp() will be the
|
||
* judge of that).
|
||
*/
|
||
rcu_report_qs_rdp(rdp);
|
||
}
|
||
|
||
/* Return true if callback-invocation time limit exceeded. */
|
||
static bool rcu_do_batch_check_time(long count, long tlimit,
|
||
bool jlimit_check, unsigned long jlimit)
|
||
{
|
||
// Invoke local_clock() only once per 32 consecutive callbacks.
|
||
return unlikely(tlimit) &&
|
||
(!likely(count & 31) ||
|
||
(IS_ENABLED(CONFIG_RCU_DOUBLE_CHECK_CB_TIME) &&
|
||
jlimit_check && time_after(jiffies, jlimit))) &&
|
||
local_clock() >= tlimit;
|
||
}
|
||
|
||
/*
|
||
* Invoke any RCU callbacks that have made it to the end of their grace
|
||
* period. Throttle as specified by rdp->blimit.
|
||
*/
|
||
static void rcu_do_batch(struct rcu_data *rdp)
|
||
{
|
||
long bl;
|
||
long count = 0;
|
||
int div;
|
||
bool __maybe_unused empty;
|
||
unsigned long flags;
|
||
unsigned long jlimit;
|
||
bool jlimit_check = false;
|
||
long pending;
|
||
struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
|
||
struct rcu_head *rhp;
|
||
long tlimit = 0;
|
||
|
||
/* If no callbacks are ready, just return. */
|
||
if (!rcu_segcblist_ready_cbs(&rdp->cblist)) {
|
||
trace_rcu_batch_start(rcu_state.name,
|
||
rcu_segcblist_n_cbs(&rdp->cblist), 0);
|
||
trace_rcu_batch_end(rcu_state.name, 0,
|
||
!rcu_segcblist_empty(&rdp->cblist),
|
||
need_resched(), is_idle_task(current),
|
||
rcu_is_callbacks_kthread(rdp));
|
||
return;
|
||
}
|
||
|
||
/*
|
||
* Extract the list of ready callbacks, disabling IRQs to prevent
|
||
* races with call_rcu() from interrupt handlers. Leave the
|
||
* callback counts, as rcu_barrier() needs to be conservative.
|
||
*
|
||
* Callbacks execution is fully ordered against preceding grace period
|
||
* completion (materialized by rnp->gp_seq update) thanks to the
|
||
* smp_mb__after_unlock_lock() upon node locking required for callbacks
|
||
* advancing. In NOCB mode this ordering is then further relayed through
|
||
* the nocb locking that protects both callbacks advancing and extraction.
|
||
*/
|
||
rcu_nocb_lock_irqsave(rdp, flags);
|
||
WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
|
||
pending = rcu_segcblist_get_seglen(&rdp->cblist, RCU_DONE_TAIL);
|
||
div = READ_ONCE(rcu_divisor);
|
||
div = div < 0 ? 7 : div > sizeof(long) * 8 - 2 ? sizeof(long) * 8 - 2 : div;
|
||
bl = max(rdp->blimit, pending >> div);
|
||
if ((in_serving_softirq() || rdp->rcu_cpu_kthread_status == RCU_KTHREAD_RUNNING) &&
|
||
(IS_ENABLED(CONFIG_RCU_DOUBLE_CHECK_CB_TIME) || unlikely(bl > 100))) {
|
||
const long npj = NSEC_PER_SEC / HZ;
|
||
long rrn = READ_ONCE(rcu_resched_ns);
|
||
|
||
rrn = rrn < NSEC_PER_MSEC ? NSEC_PER_MSEC : rrn > NSEC_PER_SEC ? NSEC_PER_SEC : rrn;
|
||
tlimit = local_clock() + rrn;
|
||
jlimit = jiffies + (rrn + npj + 1) / npj;
|
||
jlimit_check = true;
|
||
}
|
||
trace_rcu_batch_start(rcu_state.name,
|
||
rcu_segcblist_n_cbs(&rdp->cblist), bl);
|
||
rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);
|
||
if (rcu_rdp_is_offloaded(rdp))
|
||
rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
|
||
|
||
trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbDequeued"));
|
||
rcu_nocb_unlock_irqrestore(rdp, flags);
|
||
|
||
/* Invoke callbacks. */
|
||
tick_dep_set_task(current, TICK_DEP_BIT_RCU);
|
||
rhp = rcu_cblist_dequeue(&rcl);
|
||
|
||
for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) {
|
||
rcu_callback_t f;
|
||
|
||
count++;
|
||
debug_rcu_head_unqueue(rhp);
|
||
|
||
rcu_lock_acquire(&rcu_callback_map);
|
||
trace_rcu_invoke_callback(rcu_state.name, rhp);
|
||
|
||
f = rhp->func;
|
||
debug_rcu_head_callback(rhp);
|
||
WRITE_ONCE(rhp->func, (rcu_callback_t)0L);
|
||
f(rhp);
|
||
|
||
rcu_lock_release(&rcu_callback_map);
|
||
|
||
/*
|
||
* Stop only if limit reached and CPU has something to do.
|
||
*/
|
||
if (in_serving_softirq()) {
|
||
if (count >= bl && (need_resched() || !is_idle_task(current)))
|
||
break;
|
||
/*
|
||
* Make sure we don't spend too much time here and deprive other
|
||
* softirq vectors of CPU cycles.
|
||
*/
|
||
if (rcu_do_batch_check_time(count, tlimit, jlimit_check, jlimit))
|
||
break;
|
||
} else {
|
||
// In rcuc/rcuoc context, so no worries about
|
||
// depriving other softirq vectors of CPU cycles.
|
||
local_bh_enable();
|
||
lockdep_assert_irqs_enabled();
|
||
cond_resched_tasks_rcu_qs();
|
||
lockdep_assert_irqs_enabled();
|
||
local_bh_disable();
|
||
// But rcuc kthreads can delay quiescent-state
|
||
// reporting, so check time limits for them.
|
||
if (rdp->rcu_cpu_kthread_status == RCU_KTHREAD_RUNNING &&
|
||
rcu_do_batch_check_time(count, tlimit, jlimit_check, jlimit)) {
|
||
rdp->rcu_cpu_has_work = 1;
|
||
break;
|
||
}
|
||
}
|
||
}
|
||
|
||
rcu_nocb_lock_irqsave(rdp, flags);
|
||
rdp->n_cbs_invoked += count;
|
||
trace_rcu_batch_end(rcu_state.name, count, !!rcl.head, need_resched(),
|
||
is_idle_task(current), rcu_is_callbacks_kthread(rdp));
|
||
|
||
/* Update counts and requeue any remaining callbacks. */
|
||
rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl);
|
||
rcu_segcblist_add_len(&rdp->cblist, -count);
|
||
|
||
/* Reinstate batch limit if we have worked down the excess. */
|
||
count = rcu_segcblist_n_cbs(&rdp->cblist);
|
||
if (rdp->blimit >= DEFAULT_MAX_RCU_BLIMIT && count <= qlowmark)
|
||
rdp->blimit = blimit;
|
||
|
||
/* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
|
||
if (count == 0 && rdp->qlen_last_fqs_check != 0) {
|
||
rdp->qlen_last_fqs_check = 0;
|
||
rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
|
||
} else if (count < rdp->qlen_last_fqs_check - qhimark)
|
||
rdp->qlen_last_fqs_check = count;
|
||
|
||
/*
|
||
* The following usually indicates a double call_rcu(). To track
|
||
* this down, try building with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y.
|
||
*/
|
||
empty = rcu_segcblist_empty(&rdp->cblist);
|
||
WARN_ON_ONCE(count == 0 && !empty);
|
||
WARN_ON_ONCE(!IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
|
||
count != 0 && empty);
|
||
WARN_ON_ONCE(count == 0 && rcu_segcblist_n_segment_cbs(&rdp->cblist) != 0);
|
||
WARN_ON_ONCE(!empty && rcu_segcblist_n_segment_cbs(&rdp->cblist) == 0);
|
||
|
||
rcu_nocb_unlock_irqrestore(rdp, flags);
|
||
|
||
tick_dep_clear_task(current, TICK_DEP_BIT_RCU);
|
||
}
|
||
|
||
/*
|
||
* This function is invoked from each scheduling-clock interrupt,
|
||
* and checks to see if this CPU is in a non-context-switch quiescent
|
||
* state, for example, user mode or idle loop. It also schedules RCU
|
||
* core processing. If the current grace period has gone on too long,
|
||
* it will ask the scheduler to manufacture a context switch for the sole
|
||
* purpose of providing the needed quiescent state.
|
||
*/
|
||
void rcu_sched_clock_irq(int user)
|
||
{
|
||
unsigned long j;
|
||
|
||
if (IS_ENABLED(CONFIG_PROVE_RCU)) {
|
||
j = jiffies;
|
||
WARN_ON_ONCE(time_before(j, __this_cpu_read(rcu_data.last_sched_clock)));
|
||
__this_cpu_write(rcu_data.last_sched_clock, j);
|
||
}
|
||
trace_rcu_utilization(TPS("Start scheduler-tick"));
|
||
lockdep_assert_irqs_disabled();
|
||
raw_cpu_inc(rcu_data.ticks_this_gp);
|
||
/* The load-acquire pairs with the store-release setting to true. */
|
||
if (smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) {
|
||
/* Idle and userspace execution already are quiescent states. */
|
||
if (!rcu_is_cpu_rrupt_from_idle() && !user) {
|
||
set_tsk_need_resched(current);
|
||
set_preempt_need_resched();
|
||
}
|
||
__this_cpu_write(rcu_data.rcu_urgent_qs, false);
|
||
}
|
||
rcu_flavor_sched_clock_irq(user);
|
||
if (rcu_pending(user))
|
||
invoke_rcu_core();
|
||
if (user || rcu_is_cpu_rrupt_from_idle())
|
||
rcu_note_voluntary_context_switch(current);
|
||
lockdep_assert_irqs_disabled();
|
||
|
||
trace_rcu_utilization(TPS("End scheduler-tick"));
|
||
}
|
||
|
||
/*
|
||
* Scan the leaf rcu_node structures. For each structure on which all
|
||
* CPUs have reported a quiescent state and on which there are tasks
|
||
* blocking the current grace period, initiate RCU priority boosting.
|
||
* Otherwise, invoke the specified function to check dyntick state for
|
||
* each CPU that has not yet reported a quiescent state.
|
||
*/
|
||
static void force_qs_rnp(int (*f)(struct rcu_data *rdp))
|
||
{
|
||
int cpu;
|
||
unsigned long flags;
|
||
struct rcu_node *rnp;
|
||
|
||
rcu_state.cbovld = rcu_state.cbovldnext;
|
||
rcu_state.cbovldnext = false;
|
||
rcu_for_each_leaf_node(rnp) {
|
||
unsigned long mask = 0;
|
||
unsigned long rsmask = 0;
|
||
|
||
cond_resched_tasks_rcu_qs();
|
||
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
||
rcu_state.cbovldnext |= !!rnp->cbovldmask;
|
||
if (rnp->qsmask == 0) {
|
||
if (rcu_preempt_blocked_readers_cgp(rnp)) {
|
||
/*
|
||
* No point in scanning bits because they
|
||
* are all zero. But we might need to
|
||
* priority-boost blocked readers.
|
||
*/
|
||
rcu_initiate_boost(rnp, flags);
|
||
/* rcu_initiate_boost() releases rnp->lock */
|
||
continue;
|
||
}
|
||
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
||
continue;
|
||
}
|
||
for_each_leaf_node_cpu_mask(rnp, cpu, rnp->qsmask) {
|
||
struct rcu_data *rdp;
|
||
int ret;
|
||
|
||
rdp = per_cpu_ptr(&rcu_data, cpu);
|
||
ret = f(rdp);
|
||
if (ret > 0) {
|
||
mask |= rdp->grpmask;
|
||
rcu_disable_urgency_upon_qs(rdp);
|
||
}
|
||
if (ret < 0)
|
||
rsmask |= rdp->grpmask;
|
||
}
|
||
if (mask != 0) {
|
||
/* Idle/offline CPUs, report (releases rnp->lock). */
|
||
rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
|
||
} else {
|
||
/* Nothing to do here, so just drop the lock. */
|
||
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
||
}
|
||
|
||
for_each_leaf_node_cpu_mask(rnp, cpu, rsmask)
|
||
resched_cpu(cpu);
|
||
}
|
||
}
|
||
|
||
/*
|
||
* Force quiescent states on reluctant CPUs, and also detect which
|
||
* CPUs are in dyntick-idle mode.
|
||
*/
|
||
void rcu_force_quiescent_state(void)
|
||
{
|
||
unsigned long flags;
|
||
bool ret;
|
||
struct rcu_node *rnp;
|
||
struct rcu_node *rnp_old = NULL;
|
||
|
||
if (!rcu_gp_in_progress())
|
||
return;
|
||
/* Funnel through hierarchy to reduce memory contention. */
|
||
rnp = raw_cpu_read(rcu_data.mynode);
|
||
for (; rnp != NULL; rnp = rnp->parent) {
|
||
ret = (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) ||
|
||
!raw_spin_trylock(&rnp->fqslock);
|
||
if (rnp_old != NULL)
|
||
raw_spin_unlock(&rnp_old->fqslock);
|
||
if (ret)
|
||
return;
|
||
rnp_old = rnp;
|
||
}
|
||
/* rnp_old == rcu_get_root(), rnp == NULL. */
|
||
|
||
/* Reached the root of the rcu_node tree, acquire lock. */
|
||
raw_spin_lock_irqsave_rcu_node(rnp_old, flags);
|
||
raw_spin_unlock(&rnp_old->fqslock);
|
||
if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
|
||
raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
|
||
return; /* Someone beat us to it. */
|
||
}
|
||
WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_FQS);
|
||
raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
|
||
rcu_gp_kthread_wake();
|
||
}
|
||
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
|
||
|
||
// Workqueue handler for an RCU reader for kernels enforcing struct RCU
|
||
// grace periods.
|
||
static void strict_work_handler(struct work_struct *work)
|
||
{
|
||
rcu_read_lock();
|
||
rcu_read_unlock();
|
||
}
|
||
|
||
/* Perform RCU core processing work for the current CPU. */
|
||
static __latent_entropy void rcu_core(void)
|
||
{
|
||
unsigned long flags;
|
||
struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
|
||
struct rcu_node *rnp = rdp->mynode;
|
||
|
||
if (cpu_is_offline(smp_processor_id()))
|
||
return;
|
||
trace_rcu_utilization(TPS("Start RCU core"));
|
||
WARN_ON_ONCE(!rdp->beenonline);
|
||
|
||
/* Report any deferred quiescent states if preemption enabled. */
|
||
if (IS_ENABLED(CONFIG_PREEMPT_COUNT) && (!(preempt_count() & PREEMPT_MASK))) {
|
||
rcu_preempt_deferred_qs(current);
|
||
} else if (rcu_preempt_need_deferred_qs(current)) {
|
||
set_tsk_need_resched(current);
|
||
set_preempt_need_resched();
|
||
}
|
||
|
||
/* Update RCU state based on any recent quiescent states. */
|
||
rcu_check_quiescent_state(rdp);
|
||
|
||
/* No grace period and unregistered callbacks? */
|
||
if (!rcu_gp_in_progress() &&
|
||
rcu_segcblist_is_enabled(&rdp->cblist) && !rcu_rdp_is_offloaded(rdp)) {
|
||
local_irq_save(flags);
|
||
if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
|
||
rcu_accelerate_cbs_unlocked(rnp, rdp);
|
||
local_irq_restore(flags);
|
||
}
|
||
|
||
rcu_check_gp_start_stall(rnp, rdp, rcu_jiffies_till_stall_check());
|
||
|
||
/* If there are callbacks ready, invoke them. */
|
||
if (!rcu_rdp_is_offloaded(rdp) && rcu_segcblist_ready_cbs(&rdp->cblist) &&
|
||
likely(READ_ONCE(rcu_scheduler_fully_active))) {
|
||
rcu_do_batch(rdp);
|
||
/* Re-invoke RCU core processing if there are callbacks remaining. */
|
||
if (rcu_segcblist_ready_cbs(&rdp->cblist))
|
||
invoke_rcu_core();
|
||
}
|
||
|
||
/* Do any needed deferred wakeups of rcuo kthreads. */
|
||
do_nocb_deferred_wakeup(rdp);
|
||
trace_rcu_utilization(TPS("End RCU core"));
|
||
|
||
// If strict GPs, schedule an RCU reader in a clean environment.
|
||
if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
|
||
queue_work_on(rdp->cpu, rcu_gp_wq, &rdp->strict_work);
|
||
}
|
||
|
||
static void rcu_core_si(void)
|
||
{
|
||
rcu_core();
|
||
}
|
||
|
||
static void rcu_wake_cond(struct task_struct *t, int status)
|
||
{
|
||
/*
|
||
* If the thread is yielding, only wake it when this
|
||
* is invoked from idle
|
||
*/
|
||
if (t && (status != RCU_KTHREAD_YIELDING || is_idle_task(current)))
|
||
wake_up_process(t);
|
||
}
|
||
|
||
static void invoke_rcu_core_kthread(void)
|
||
{
|
||
struct task_struct *t;
|
||
unsigned long flags;
|
||
|
||
local_irq_save(flags);
|
||
__this_cpu_write(rcu_data.rcu_cpu_has_work, 1);
|
||
t = __this_cpu_read(rcu_data.rcu_cpu_kthread_task);
|
||
if (t != NULL && t != current)
|
||
rcu_wake_cond(t, __this_cpu_read(rcu_data.rcu_cpu_kthread_status));
|
||
local_irq_restore(flags);
|
||
}
|
||
|
||
/*
|
||
* Wake up this CPU's rcuc kthread to do RCU core processing.
|
||
*/
|
||
static void invoke_rcu_core(void)
|
||
{
|
||
if (!cpu_online(smp_processor_id()))
|
||
return;
|
||
if (use_softirq)
|
||
raise_softirq(RCU_SOFTIRQ);
|
||
else
|
||
invoke_rcu_core_kthread();
|
||
}
|
||
|
||
static void rcu_cpu_kthread_park(unsigned int cpu)
|
||
{
|
||
per_cpu(rcu_data.rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
|
||
}
|
||
|
||
static int rcu_cpu_kthread_should_run(unsigned int cpu)
|
||
{
|
||
return __this_cpu_read(rcu_data.rcu_cpu_has_work);
|
||
}
|
||
|
||
/*
|
||
* Per-CPU kernel thread that invokes RCU callbacks. This replaces
|
||
* the RCU softirq used in configurations of RCU that do not support RCU
|
||
* priority boosting.
|
||
*/
|
||
static void rcu_cpu_kthread(unsigned int cpu)
|
||
{
|
||
unsigned int *statusp = this_cpu_ptr(&rcu_data.rcu_cpu_kthread_status);
|
||
char work, *workp = this_cpu_ptr(&rcu_data.rcu_cpu_has_work);
|
||
unsigned long *j = this_cpu_ptr(&rcu_data.rcuc_activity);
|
||
int spincnt;
|
||
|
||
trace_rcu_utilization(TPS("Start CPU kthread@rcu_run"));
|
||
for (spincnt = 0; spincnt < 10; spincnt++) {
|
||
WRITE_ONCE(*j, jiffies);
|
||
local_bh_disable();
|
||
*statusp = RCU_KTHREAD_RUNNING;
|
||
local_irq_disable();
|
||
work = *workp;
|
||
WRITE_ONCE(*workp, 0);
|
||
local_irq_enable();
|
||
if (work)
|
||
rcu_core();
|
||
local_bh_enable();
|
||
if (!READ_ONCE(*workp)) {
|
||
trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
|
||
*statusp = RCU_KTHREAD_WAITING;
|
||
return;
|
||
}
|
||
}
|
||
*statusp = RCU_KTHREAD_YIELDING;
|
||
trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
|
||
schedule_timeout_idle(2);
|
||
trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
|
||
*statusp = RCU_KTHREAD_WAITING;
|
||
WRITE_ONCE(*j, jiffies);
|
||
}
|
||
|
||
static struct smp_hotplug_thread rcu_cpu_thread_spec = {
|
||
.store = &rcu_data.rcu_cpu_kthread_task,
|
||
.thread_should_run = rcu_cpu_kthread_should_run,
|
||
.thread_fn = rcu_cpu_kthread,
|
||
.thread_comm = "rcuc/%u",
|
||
.setup = rcu_cpu_kthread_setup,
|
||
.park = rcu_cpu_kthread_park,
|
||
};
|
||
|
||
/*
|
||
* Spawn per-CPU RCU core processing kthreads.
|
||
*/
|
||
static int __init rcu_spawn_core_kthreads(void)
|
||
{
|
||
int cpu;
|
||
|
||
for_each_possible_cpu(cpu)
|
||
per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0;
|
||
if (use_softirq)
|
||
return 0;
|
||
WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec),
|
||
"%s: Could not start rcuc kthread, OOM is now expected behavior\n", __func__);
|
||
return 0;
|
||
}
|
||
|
||
static void rcutree_enqueue(struct rcu_data *rdp, struct rcu_head *head, rcu_callback_t func)
|
||
{
|
||
rcu_segcblist_enqueue(&rdp->cblist, head);
|
||
if (__is_kvfree_rcu_offset((unsigned long)func))
|
||
trace_rcu_kvfree_callback(rcu_state.name, head,
|
||
(unsigned long)func,
|
||
rcu_segcblist_n_cbs(&rdp->cblist));
|
||
else
|
||
trace_rcu_callback(rcu_state.name, head,
|
||
rcu_segcblist_n_cbs(&rdp->cblist));
|
||
trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCBQueued"));
|
||
}
|
||
|
||
/*
|
||
* Handle any core-RCU processing required by a call_rcu() invocation.
|
||
*/
|
||
static void call_rcu_core(struct rcu_data *rdp, struct rcu_head *head,
|
||
rcu_callback_t func, unsigned long flags)
|
||
{
|
||
rcutree_enqueue(rdp, head, func);
|
||
/*
|
||
* If called from an extended quiescent state, invoke the RCU
|
||
* core in order to force a re-evaluation of RCU's idleness.
|
||
*/
|
||
if (!rcu_is_watching())
|
||
invoke_rcu_core();
|
||
|
||
/* If interrupts were disabled or CPU offline, don't invoke RCU core. */
|
||
if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
|
||
return;
|
||
|
||
/*
|
||
* Force the grace period if too many callbacks or too long waiting.
|
||
* Enforce hysteresis, and don't invoke rcu_force_quiescent_state()
|
||
* if some other CPU has recently done so. Also, don't bother
|
||
* invoking rcu_force_quiescent_state() if the newly enqueued callback
|
||
* is the only one waiting for a grace period to complete.
|
||
*/
|
||
if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) >
|
||
rdp->qlen_last_fqs_check + qhimark)) {
|
||
|
||
/* Are we ignoring a completed grace period? */
|
||
note_gp_changes(rdp);
|
||
|
||
/* Start a new grace period if one not already started. */
|
||
if (!rcu_gp_in_progress()) {
|
||
rcu_accelerate_cbs_unlocked(rdp->mynode, rdp);
|
||
} else {
|
||
/* Give the grace period a kick. */
|
||
rdp->blimit = DEFAULT_MAX_RCU_BLIMIT;
|
||
if (READ_ONCE(rcu_state.n_force_qs) == rdp->n_force_qs_snap &&
|
||
rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
|
||
rcu_force_quiescent_state();
|
||
rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
|
||
rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
|
||
}
|
||
}
|
||
}
|
||
|
||
/*
|
||
* RCU callback function to leak a callback.
|
||
*/
|
||
static void rcu_leak_callback(struct rcu_head *rhp)
|
||
{
|
||
}
|
||
|
||
/*
|
||
* Check and if necessary update the leaf rcu_node structure's
|
||
* ->cbovldmask bit corresponding to the current CPU based on that CPU's
|
||
* number of queued RCU callbacks. The caller must hold the leaf rcu_node
|
||
* structure's ->lock.
|
||
*/
|
||
static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp)
|
||
{
|
||
raw_lockdep_assert_held_rcu_node(rnp);
|
||
if (qovld_calc <= 0)
|
||
return; // Early boot and wildcard value set.
|
||
if (rcu_segcblist_n_cbs(&rdp->cblist) >= qovld_calc)
|
||
WRITE_ONCE(rnp->cbovldmask, rnp->cbovldmask | rdp->grpmask);
|
||
else
|
||
WRITE_ONCE(rnp->cbovldmask, rnp->cbovldmask & ~rdp->grpmask);
|
||
}
|
||
|
||
/*
|
||
* Check and if necessary update the leaf rcu_node structure's
|
||
* ->cbovldmask bit corresponding to the current CPU based on that CPU's
|
||
* number of queued RCU callbacks. No locks need be held, but the
|
||
* caller must have disabled interrupts.
|
||
*
|
||
* Note that this function ignores the possibility that there are a lot
|
||
* of callbacks all of which have already seen the end of their respective
|
||
* grace periods. This omission is due to the need for no-CBs CPUs to
|
||
* be holding ->nocb_lock to do this check, which is too heavy for a
|
||
* common-case operation.
|
||
*/
|
||
static void check_cb_ovld(struct rcu_data *rdp)
|
||
{
|
||
struct rcu_node *const rnp = rdp->mynode;
|
||
|
||
if (qovld_calc <= 0 ||
|
||
((rcu_segcblist_n_cbs(&rdp->cblist) >= qovld_calc) ==
|
||
!!(READ_ONCE(rnp->cbovldmask) & rdp->grpmask)))
|
||
return; // Early boot wildcard value or already set correctly.
|
||
raw_spin_lock_rcu_node(rnp);
|
||
check_cb_ovld_locked(rdp, rnp);
|
||
raw_spin_unlock_rcu_node(rnp);
|
||
}
|
||
|
||
static void
|
||
__call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in)
|
||
{
|
||
static atomic_t doublefrees;
|
||
unsigned long flags;
|
||
bool lazy;
|
||
struct rcu_data *rdp;
|
||
|
||
/* Misaligned rcu_head! */
|
||
WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
|
||
|
||
if (debug_rcu_head_queue(head)) {
|
||
/*
|
||
* Probable double call_rcu(), so leak the callback.
|
||
* Use rcu:rcu_callback trace event to find the previous
|
||
* time callback was passed to call_rcu().
|
||
*/
|
||
if (atomic_inc_return(&doublefrees) < 4) {
|
||
pr_err("%s(): Double-freed CB %p->%pS()!!! ", __func__, head, head->func);
|
||
mem_dump_obj(head);
|
||
}
|
||
WRITE_ONCE(head->func, rcu_leak_callback);
|
||
return;
|
||
}
|
||
head->func = func;
|
||
head->next = NULL;
|
||
kasan_record_aux_stack_noalloc(head);
|
||
local_irq_save(flags);
|
||
rdp = this_cpu_ptr(&rcu_data);
|
||
lazy = lazy_in && !rcu_async_should_hurry();
|
||
|
||
/* Add the callback to our list. */
|
||
if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist))) {
|
||
// This can trigger due to call_rcu() from offline CPU:
|
||
WARN_ON_ONCE(rcu_scheduler_active != RCU_SCHEDULER_INACTIVE);
|
||
WARN_ON_ONCE(!rcu_is_watching());
|
||
// Very early boot, before rcu_init(). Initialize if needed
|
||
// and then drop through to queue the callback.
|
||
if (rcu_segcblist_empty(&rdp->cblist))
|
||
rcu_segcblist_init(&rdp->cblist);
|
||
}
|
||
|
||
check_cb_ovld(rdp);
|
||
|
||
if (unlikely(rcu_rdp_is_offloaded(rdp)))
|
||
call_rcu_nocb(rdp, head, func, flags, lazy);
|
||
else
|
||
call_rcu_core(rdp, head, func, flags);
|
||
local_irq_restore(flags);
|
||
}
|
||
|
||
#ifdef CONFIG_RCU_LAZY
|
||
static bool enable_rcu_lazy __read_mostly = !IS_ENABLED(CONFIG_RCU_LAZY_DEFAULT_OFF);
|
||
module_param(enable_rcu_lazy, bool, 0444);
|
||
|
||
/**
|
||
* call_rcu_hurry() - Queue RCU callback for invocation after grace period, and
|
||
* flush all lazy callbacks (including the new one) to the main ->cblist while
|
||
* doing so.
|
||
*
|
||
* @head: structure to be used for queueing the RCU updates.
|
||
* @func: actual callback function to be invoked after the grace period
|
||
*
|
||
* The callback function will be invoked some time after a full grace
|
||
* period elapses, in other words after all pre-existing RCU read-side
|
||
* critical sections have completed.
|
||
*
|
||
* Use this API instead of call_rcu() if you don't want the callback to be
|
||
* invoked after very long periods of time, which can happen on systems without
|
||
* memory pressure and on systems which are lightly loaded or mostly idle.
|
||
* This function will cause callbacks to be invoked sooner than later at the
|
||
* expense of extra power. Other than that, this function is identical to, and
|
||
* reuses call_rcu()'s logic. Refer to call_rcu() for more details about memory
|
||
* ordering and other functionality.
|
||
*/
|
||
void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func)
|
||
{
|
||
__call_rcu_common(head, func, false);
|
||
}
|
||
EXPORT_SYMBOL_GPL(call_rcu_hurry);
|
||
#else
|
||
#define enable_rcu_lazy false
|
||
#endif
|
||
|
||
/**
|
||
* call_rcu() - Queue an RCU callback for invocation after a grace period.
|
||
* By default the callbacks are 'lazy' and are kept hidden from the main
|
||
* ->cblist to prevent starting of grace periods too soon.
|
||
* If you desire grace periods to start very soon, use call_rcu_hurry().
|
||
*
|
||
* @head: structure to be used for queueing the RCU updates.
|
||
* @func: actual callback function to be invoked after the grace period
|
||
*
|
||
* The callback function will be invoked some time after a full grace
|
||
* period elapses, in other words after all pre-existing RCU read-side
|
||
* critical sections have completed. However, the callback function
|
||
* might well execute concurrently with RCU read-side critical sections
|
||
* that started after call_rcu() was invoked.
|
||
*
|
||
* RCU read-side critical sections are delimited by rcu_read_lock()
|
||
* and rcu_read_unlock(), and may be nested. In addition, but only in
|
||
* v5.0 and later, regions of code across which interrupts, preemption,
|
||
* or softirqs have been disabled also serve as RCU read-side critical
|
||
* sections. This includes hardware interrupt handlers, softirq handlers,
|
||
* and NMI handlers.
|
||
*
|
||
* Note that all CPUs must agree that the grace period extended beyond
|
||
* all pre-existing RCU read-side critical section. On systems with more
|
||
* than one CPU, this means that when "func()" is invoked, each CPU is
|
||
* guaranteed to have executed a full memory barrier since the end of its
|
||
* last RCU read-side critical section whose beginning preceded the call
|
||
* to call_rcu(). It also means that each CPU executing an RCU read-side
|
||
* critical section that continues beyond the start of "func()" must have
|
||
* executed a memory barrier after the call_rcu() but before the beginning
|
||
* of that RCU read-side critical section. Note that these guarantees
|
||
* include CPUs that are offline, idle, or executing in user mode, as
|
||
* well as CPUs that are executing in the kernel.
|
||
*
|
||
* Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
|
||
* resulting RCU callback function "func()", then both CPU A and CPU B are
|
||
* guaranteed to execute a full memory barrier during the time interval
|
||
* between the call to call_rcu() and the invocation of "func()" -- even
|
||
* if CPU A and CPU B are the same CPU (but again only if the system has
|
||
* more than one CPU).
|
||
*
|
||
* Implementation of these memory-ordering guarantees is described here:
|
||
* Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
|
||
*/
|
||
void call_rcu(struct rcu_head *head, rcu_callback_t func)
|
||
{
|
||
__call_rcu_common(head, func, enable_rcu_lazy);
|
||
}
|
||
EXPORT_SYMBOL_GPL(call_rcu);
|
||
|
||
/* Maximum number of jiffies to wait before draining a batch. */
|
||
#define KFREE_DRAIN_JIFFIES (5 * HZ)
|
||
#define KFREE_N_BATCHES 2
|
||
#define FREE_N_CHANNELS 2
|
||
|
||
/**
|
||
* struct kvfree_rcu_bulk_data - single block to store kvfree_rcu() pointers
|
||
* @list: List node. All blocks are linked between each other
|
||
* @gp_snap: Snapshot of RCU state for objects placed to this bulk
|
||
* @nr_records: Number of active pointers in the array
|
||
* @records: Array of the kvfree_rcu() pointers
|
||
*/
|
||
struct kvfree_rcu_bulk_data {
|
||
struct list_head list;
|
||
struct rcu_gp_oldstate gp_snap;
|
||
unsigned long nr_records;
|
||
void *records[] __counted_by(nr_records);
|
||
};
|
||
|
||
/*
|
||
* This macro defines how many entries the "records" array
|
||
* will contain. It is based on the fact that the size of
|
||
* kvfree_rcu_bulk_data structure becomes exactly one page.
|
||
*/
|
||
#define KVFREE_BULK_MAX_ENTR \
|
||
((PAGE_SIZE - sizeof(struct kvfree_rcu_bulk_data)) / sizeof(void *))
|
||
|
||
/**
|
||
* struct kfree_rcu_cpu_work - single batch of kfree_rcu() requests
|
||
* @rcu_work: Let queue_rcu_work() invoke workqueue handler after grace period
|
||
* @head_free: List of kfree_rcu() objects waiting for a grace period
|
||
* @head_free_gp_snap: Grace-period snapshot to check for attempted premature frees.
|
||
* @bulk_head_free: Bulk-List of kvfree_rcu() objects waiting for a grace period
|
||
* @krcp: Pointer to @kfree_rcu_cpu structure
|
||
*/
|
||
|
||
struct kfree_rcu_cpu_work {
|
||
struct rcu_work rcu_work;
|
||
struct rcu_head *head_free;
|
||
struct rcu_gp_oldstate head_free_gp_snap;
|
||
struct list_head bulk_head_free[FREE_N_CHANNELS];
|
||
struct kfree_rcu_cpu *krcp;
|
||
};
|
||
|
||
/**
|
||
* struct kfree_rcu_cpu - batch up kfree_rcu() requests for RCU grace period
|
||
* @head: List of kfree_rcu() objects not yet waiting for a grace period
|
||
* @head_gp_snap: Snapshot of RCU state for objects placed to "@head"
|
||
* @bulk_head: Bulk-List of kvfree_rcu() objects not yet waiting for a grace period
|
||
* @krw_arr: Array of batches of kfree_rcu() objects waiting for a grace period
|
||
* @lock: Synchronize access to this structure
|
||
* @monitor_work: Promote @head to @head_free after KFREE_DRAIN_JIFFIES
|
||
* @initialized: The @rcu_work fields have been initialized
|
||
* @head_count: Number of objects in rcu_head singular list
|
||
* @bulk_count: Number of objects in bulk-list
|
||
* @bkvcache:
|
||
* A simple cache list that contains objects for reuse purpose.
|
||
* In order to save some per-cpu space the list is singular.
|
||
* Even though it is lockless an access has to be protected by the
|
||
* per-cpu lock.
|
||
* @page_cache_work: A work to refill the cache when it is empty
|
||
* @backoff_page_cache_fill: Delay cache refills
|
||
* @work_in_progress: Indicates that page_cache_work is running
|
||
* @hrtimer: A hrtimer for scheduling a page_cache_work
|
||
* @nr_bkv_objs: number of allocated objects at @bkvcache.
|
||
*
|
||
* This is a per-CPU structure. The reason that it is not included in
|
||
* the rcu_data structure is to permit this code to be extracted from
|
||
* the RCU files. Such extraction could allow further optimization of
|
||
* the interactions with the slab allocators.
|
||
*/
|
||
struct kfree_rcu_cpu {
|
||
// Objects queued on a linked list
|
||
// through their rcu_head structures.
|
||
struct rcu_head *head;
|
||
unsigned long head_gp_snap;
|
||
atomic_t head_count;
|
||
|
||
// Objects queued on a bulk-list.
|
||
struct list_head bulk_head[FREE_N_CHANNELS];
|
||
atomic_t bulk_count[FREE_N_CHANNELS];
|
||
|
||
struct kfree_rcu_cpu_work krw_arr[KFREE_N_BATCHES];
|
||
raw_spinlock_t lock;
|
||
struct delayed_work monitor_work;
|
||
bool initialized;
|
||
|
||
struct delayed_work page_cache_work;
|
||
atomic_t backoff_page_cache_fill;
|
||
atomic_t work_in_progress;
|
||
struct hrtimer hrtimer;
|
||
|
||
struct llist_head bkvcache;
|
||
int nr_bkv_objs;
|
||
};
|
||
|
||
static DEFINE_PER_CPU(struct kfree_rcu_cpu, krc) = {
|
||
.lock = __RAW_SPIN_LOCK_UNLOCKED(krc.lock),
|
||
};
|
||
|
||
static __always_inline void
|
||
debug_rcu_bhead_unqueue(struct kvfree_rcu_bulk_data *bhead)
|
||
{
|
||
#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
|
||
int i;
|
||
|
||
for (i = 0; i < bhead->nr_records; i++)
|
||
debug_rcu_head_unqueue((struct rcu_head *)(bhead->records[i]));
|
||
#endif
|
||
}
|
||
|
||
static inline struct kfree_rcu_cpu *
|
||
krc_this_cpu_lock(unsigned long *flags)
|
||
{
|
||
struct kfree_rcu_cpu *krcp;
|
||
|
||
local_irq_save(*flags); // For safely calling this_cpu_ptr().
|
||
krcp = this_cpu_ptr(&krc);
|
||
raw_spin_lock(&krcp->lock);
|
||
|
||
return krcp;
|
||
}
|
||
|
||
static inline void
|
||
krc_this_cpu_unlock(struct kfree_rcu_cpu *krcp, unsigned long flags)
|
||
{
|
||
raw_spin_unlock_irqrestore(&krcp->lock, flags);
|
||
}
|
||
|
||
static inline struct kvfree_rcu_bulk_data *
|
||
get_cached_bnode(struct kfree_rcu_cpu *krcp)
|
||
{
|
||
if (!krcp->nr_bkv_objs)
|
||
return NULL;
|
||
|
||
WRITE_ONCE(krcp->nr_bkv_objs, krcp->nr_bkv_objs - 1);
|
||
return (struct kvfree_rcu_bulk_data *)
|
||
llist_del_first(&krcp->bkvcache);
|
||
}
|
||
|
||
static inline bool
|
||
put_cached_bnode(struct kfree_rcu_cpu *krcp,
|
||
struct kvfree_rcu_bulk_data *bnode)
|
||
{
|
||
// Check the limit.
|
||
if (krcp->nr_bkv_objs >= rcu_min_cached_objs)
|
||
return false;
|
||
|
||
llist_add((struct llist_node *) bnode, &krcp->bkvcache);
|
||
WRITE_ONCE(krcp->nr_bkv_objs, krcp->nr_bkv_objs + 1);
|
||
return true;
|
||
}
|
||
|
||
static int
|
||
drain_page_cache(struct kfree_rcu_cpu *krcp)
|
||
{
|
||
unsigned long flags;
|
||
struct llist_node *page_list, *pos, *n;
|
||
int freed = 0;
|
||
|
||
if (!rcu_min_cached_objs)
|
||
return 0;
|
||
|
||
raw_spin_lock_irqsave(&krcp->lock, flags);
|
||
page_list = llist_del_all(&krcp->bkvcache);
|
||
WRITE_ONCE(krcp->nr_bkv_objs, 0);
|
||
raw_spin_unlock_irqrestore(&krcp->lock, flags);
|
||
|
||
llist_for_each_safe(pos, n, page_list) {
|
||
free_page((unsigned long)pos);
|
||
freed++;
|
||
}
|
||
|
||
return freed;
|
||
}
|
||
|
||
static void
|
||
kvfree_rcu_bulk(struct kfree_rcu_cpu *krcp,
|
||
struct kvfree_rcu_bulk_data *bnode, int idx)
|
||
{
|
||
unsigned long flags;
|
||
int i;
|
||
|
||
if (!WARN_ON_ONCE(!poll_state_synchronize_rcu_full(&bnode->gp_snap))) {
|
||
debug_rcu_bhead_unqueue(bnode);
|
||
rcu_lock_acquire(&rcu_callback_map);
|
||
if (idx == 0) { // kmalloc() / kfree().
|
||
trace_rcu_invoke_kfree_bulk_callback(
|
||
rcu_state.name, bnode->nr_records,
|
||
bnode->records);
|
||
|
||
kfree_bulk(bnode->nr_records, bnode->records);
|
||
} else { // vmalloc() / vfree().
|
||
for (i = 0; i < bnode->nr_records; i++) {
|
||
trace_rcu_invoke_kvfree_callback(
|
||
rcu_state.name, bnode->records[i], 0);
|
||
|
||
vfree(bnode->records[i]);
|
||
}
|
||
}
|
||
rcu_lock_release(&rcu_callback_map);
|
||
}
|
||
|
||
raw_spin_lock_irqsave(&krcp->lock, flags);
|
||
if (put_cached_bnode(krcp, bnode))
|
||
bnode = NULL;
|
||
raw_spin_unlock_irqrestore(&krcp->lock, flags);
|
||
|
||
if (bnode)
|
||
free_page((unsigned long) bnode);
|
||
|
||
cond_resched_tasks_rcu_qs();
|
||
}
|
||
|
||
static void
|
||
kvfree_rcu_list(struct rcu_head *head)
|
||
{
|
||
struct rcu_head *next;
|
||
|
||
for (; head; head = next) {
|
||
void *ptr = (void *) head->func;
|
||
unsigned long offset = (void *) head - ptr;
|
||
|
||
next = head->next;
|
||
debug_rcu_head_unqueue((struct rcu_head *)ptr);
|
||
rcu_lock_acquire(&rcu_callback_map);
|
||
trace_rcu_invoke_kvfree_callback(rcu_state.name, head, offset);
|
||
|
||
if (!WARN_ON_ONCE(!__is_kvfree_rcu_offset(offset)))
|
||
kvfree(ptr);
|
||
|
||
rcu_lock_release(&rcu_callback_map);
|
||
cond_resched_tasks_rcu_qs();
|
||
}
|
||
}
|
||
|
||
/*
|
||
* This function is invoked in workqueue context after a grace period.
|
||
* It frees all the objects queued on ->bulk_head_free or ->head_free.
|
||
*/
|
||
static void kfree_rcu_work(struct work_struct *work)
|
||
{
|
||
unsigned long flags;
|
||
struct kvfree_rcu_bulk_data *bnode, *n;
|
||
struct list_head bulk_head[FREE_N_CHANNELS];
|
||
struct rcu_head *head;
|
||
struct kfree_rcu_cpu *krcp;
|
||
struct kfree_rcu_cpu_work *krwp;
|
||
struct rcu_gp_oldstate head_gp_snap;
|
||
int i;
|
||
|
||
krwp = container_of(to_rcu_work(work),
|
||
struct kfree_rcu_cpu_work, rcu_work);
|
||
krcp = krwp->krcp;
|
||
|
||
raw_spin_lock_irqsave(&krcp->lock, flags);
|
||
// Channels 1 and 2.
|
||
for (i = 0; i < FREE_N_CHANNELS; i++)
|
||
list_replace_init(&krwp->bulk_head_free[i], &bulk_head[i]);
|
||
|
||
// Channel 3.
|
||
head = krwp->head_free;
|
||
krwp->head_free = NULL;
|
||
head_gp_snap = krwp->head_free_gp_snap;
|
||
raw_spin_unlock_irqrestore(&krcp->lock, flags);
|
||
|
||
// Handle the first two channels.
|
||
for (i = 0; i < FREE_N_CHANNELS; i++) {
|
||
// Start from the tail page, so a GP is likely passed for it.
|
||
list_for_each_entry_safe(bnode, n, &bulk_head[i], list)
|
||
kvfree_rcu_bulk(krcp, bnode, i);
|
||
}
|
||
|
||
/*
|
||
* This is used when the "bulk" path can not be used for the
|
||
* double-argument of kvfree_rcu(). This happens when the
|
||
* page-cache is empty, which means that objects are instead
|
||
* queued on a linked list through their rcu_head structures.
|
||
* This list is named "Channel 3".
|
||
*/
|
||
if (head && !WARN_ON_ONCE(!poll_state_synchronize_rcu_full(&head_gp_snap)))
|
||
kvfree_rcu_list(head);
|
||
}
|
||
|
||
static bool
|
||
need_offload_krc(struct kfree_rcu_cpu *krcp)
|
||
{
|
||
int i;
|
||
|
||
for (i = 0; i < FREE_N_CHANNELS; i++)
|
||
if (!list_empty(&krcp->bulk_head[i]))
|
||
return true;
|
||
|
||
return !!READ_ONCE(krcp->head);
|
||
}
|
||
|
||
static bool
|
||
need_wait_for_krwp_work(struct kfree_rcu_cpu_work *krwp)
|
||
{
|
||
int i;
|
||
|
||
for (i = 0; i < FREE_N_CHANNELS; i++)
|
||
if (!list_empty(&krwp->bulk_head_free[i]))
|
||
return true;
|
||
|
||
return !!krwp->head_free;
|
||
}
|
||
|
||
static int krc_count(struct kfree_rcu_cpu *krcp)
|
||
{
|
||
int sum = atomic_read(&krcp->head_count);
|
||
int i;
|
||
|
||
for (i = 0; i < FREE_N_CHANNELS; i++)
|
||
sum += atomic_read(&krcp->bulk_count[i]);
|
||
|
||
return sum;
|
||
}
|
||
|
||
static void
|
||
schedule_delayed_monitor_work(struct kfree_rcu_cpu *krcp)
|
||
{
|
||
long delay, delay_left;
|
||
|
||
delay = krc_count(krcp) >= KVFREE_BULK_MAX_ENTR ? 1:KFREE_DRAIN_JIFFIES;
|
||
if (delayed_work_pending(&krcp->monitor_work)) {
|
||
delay_left = krcp->monitor_work.timer.expires - jiffies;
|
||
if (delay < delay_left)
|
||
mod_delayed_work(system_unbound_wq, &krcp->monitor_work, delay);
|
||
return;
|
||
}
|
||
queue_delayed_work(system_unbound_wq, &krcp->monitor_work, delay);
|
||
}
|
||
|
||
static void
|
||
kvfree_rcu_drain_ready(struct kfree_rcu_cpu *krcp)
|
||
{
|
||
struct list_head bulk_ready[FREE_N_CHANNELS];
|
||
struct kvfree_rcu_bulk_data *bnode, *n;
|
||
struct rcu_head *head_ready = NULL;
|
||
unsigned long flags;
|
||
int i;
|
||
|
||
raw_spin_lock_irqsave(&krcp->lock, flags);
|
||
for (i = 0; i < FREE_N_CHANNELS; i++) {
|
||
INIT_LIST_HEAD(&bulk_ready[i]);
|
||
|
||
list_for_each_entry_safe_reverse(bnode, n, &krcp->bulk_head[i], list) {
|
||
if (!poll_state_synchronize_rcu_full(&bnode->gp_snap))
|
||
break;
|
||
|
||
atomic_sub(bnode->nr_records, &krcp->bulk_count[i]);
|
||
list_move(&bnode->list, &bulk_ready[i]);
|
||
}
|
||
}
|
||
|
||
if (krcp->head && poll_state_synchronize_rcu(krcp->head_gp_snap)) {
|
||
head_ready = krcp->head;
|
||
atomic_set(&krcp->head_count, 0);
|
||
WRITE_ONCE(krcp->head, NULL);
|
||
}
|
||
raw_spin_unlock_irqrestore(&krcp->lock, flags);
|
||
|
||
for (i = 0; i < FREE_N_CHANNELS; i++) {
|
||
list_for_each_entry_safe(bnode, n, &bulk_ready[i], list)
|
||
kvfree_rcu_bulk(krcp, bnode, i);
|
||
}
|
||
|
||
if (head_ready)
|
||
kvfree_rcu_list(head_ready);
|
||
}
|
||
|
||
/*
|
||
* Return: %true if a work is queued, %false otherwise.
|
||
*/
|
||
static bool
|
||
kvfree_rcu_queue_batch(struct kfree_rcu_cpu *krcp)
|
||
{
|
||
unsigned long flags;
|
||
bool queued = false;
|
||
int i, j;
|
||
|
||
raw_spin_lock_irqsave(&krcp->lock, flags);
|
||
|
||
// Attempt to start a new batch.
|
||
for (i = 0; i < KFREE_N_BATCHES; i++) {
|
||
struct kfree_rcu_cpu_work *krwp = &(krcp->krw_arr[i]);
|
||
|
||
// Try to detach bulk_head or head and attach it, only when
|
||
// all channels are free. Any channel is not free means at krwp
|
||
// there is on-going rcu work to handle krwp's free business.
|
||
if (need_wait_for_krwp_work(krwp))
|
||
continue;
|
||
|
||
// kvfree_rcu_drain_ready() might handle this krcp, if so give up.
|
||
if (need_offload_krc(krcp)) {
|
||
// Channel 1 corresponds to the SLAB-pointer bulk path.
|
||
// Channel 2 corresponds to vmalloc-pointer bulk path.
|
||
for (j = 0; j < FREE_N_CHANNELS; j++) {
|
||
if (list_empty(&krwp->bulk_head_free[j])) {
|
||
atomic_set(&krcp->bulk_count[j], 0);
|
||
list_replace_init(&krcp->bulk_head[j],
|
||
&krwp->bulk_head_free[j]);
|
||
}
|
||
}
|
||
|
||
// Channel 3 corresponds to both SLAB and vmalloc
|
||
// objects queued on the linked list.
|
||
if (!krwp->head_free) {
|
||
krwp->head_free = krcp->head;
|
||
get_state_synchronize_rcu_full(&krwp->head_free_gp_snap);
|
||
atomic_set(&krcp->head_count, 0);
|
||
WRITE_ONCE(krcp->head, NULL);
|
||
}
|
||
|
||
// One work is per one batch, so there are three
|
||
// "free channels", the batch can handle. Break
|
||
// the loop since it is done with this CPU thus
|
||
// queuing an RCU work is _always_ success here.
|
||
queued = queue_rcu_work(system_unbound_wq, &krwp->rcu_work);
|
||
WARN_ON_ONCE(!queued);
|
||
break;
|
||
}
|
||
}
|
||
|
||
raw_spin_unlock_irqrestore(&krcp->lock, flags);
|
||
return queued;
|
||
}
|
||
|
||
/*
|
||
* This function is invoked after the KFREE_DRAIN_JIFFIES timeout.
|
||
*/
|
||
static void kfree_rcu_monitor(struct work_struct *work)
|
||
{
|
||
struct kfree_rcu_cpu *krcp = container_of(work,
|
||
struct kfree_rcu_cpu, monitor_work.work);
|
||
|
||
// Drain ready for reclaim.
|
||
kvfree_rcu_drain_ready(krcp);
|
||
|
||
// Queue a batch for a rest.
|
||
kvfree_rcu_queue_batch(krcp);
|
||
|
||
// If there is nothing to detach, it means that our job is
|
||
// successfully done here. In case of having at least one
|
||
// of the channels that is still busy we should rearm the
|
||
// work to repeat an attempt. Because previous batches are
|
||
// still in progress.
|
||
if (need_offload_krc(krcp))
|
||
schedule_delayed_monitor_work(krcp);
|
||
}
|
||
|
||
static enum hrtimer_restart
|
||
schedule_page_work_fn(struct hrtimer *t)
|
||
{
|
||
struct kfree_rcu_cpu *krcp =
|
||
container_of(t, struct kfree_rcu_cpu, hrtimer);
|
||
|
||
queue_delayed_work(system_highpri_wq, &krcp->page_cache_work, 0);
|
||
return HRTIMER_NORESTART;
|
||
}
|
||
|
||
static void fill_page_cache_func(struct work_struct *work)
|
||
{
|
||
struct kvfree_rcu_bulk_data *bnode;
|
||
struct kfree_rcu_cpu *krcp =
|
||
container_of(work, struct kfree_rcu_cpu,
|
||
page_cache_work.work);
|
||
unsigned long flags;
|
||
int nr_pages;
|
||
bool pushed;
|
||
int i;
|
||
|
||
nr_pages = atomic_read(&krcp->backoff_page_cache_fill) ?
|
||
1 : rcu_min_cached_objs;
|
||
|
||
for (i = READ_ONCE(krcp->nr_bkv_objs); i < nr_pages; i++) {
|
||
bnode = (struct kvfree_rcu_bulk_data *)
|
||
__get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
|
||
|
||
if (!bnode)
|
||
break;
|
||
|
||
raw_spin_lock_irqsave(&krcp->lock, flags);
|
||
pushed = put_cached_bnode(krcp, bnode);
|
||
raw_spin_unlock_irqrestore(&krcp->lock, flags);
|
||
|
||
if (!pushed) {
|
||
free_page((unsigned long) bnode);
|
||
break;
|
||
}
|
||
}
|
||
|
||
atomic_set(&krcp->work_in_progress, 0);
|
||
atomic_set(&krcp->backoff_page_cache_fill, 0);
|
||
}
|
||
|
||
static void
|
||
run_page_cache_worker(struct kfree_rcu_cpu *krcp)
|
||
{
|
||
// If cache disabled, bail out.
|
||
if (!rcu_min_cached_objs)
|
||
return;
|
||
|
||
if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING &&
|
||
!atomic_xchg(&krcp->work_in_progress, 1)) {
|
||
if (atomic_read(&krcp->backoff_page_cache_fill)) {
|
||
queue_delayed_work(system_unbound_wq,
|
||
&krcp->page_cache_work,
|
||
msecs_to_jiffies(rcu_delay_page_cache_fill_msec));
|
||
} else {
|
||
hrtimer_init(&krcp->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
|
||
krcp->hrtimer.function = schedule_page_work_fn;
|
||
hrtimer_start(&krcp->hrtimer, 0, HRTIMER_MODE_REL);
|
||
}
|
||
}
|
||
}
|
||
|
||
// Record ptr in a page managed by krcp, with the pre-krc_this_cpu_lock()
|
||
// state specified by flags. If can_alloc is true, the caller must
|
||
// be schedulable and not be holding any locks or mutexes that might be
|
||
// acquired by the memory allocator or anything that it might invoke.
|
||
// Returns true if ptr was successfully recorded, else the caller must
|
||
// use a fallback.
|
||
static inline bool
|
||
add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp,
|
||
unsigned long *flags, void *ptr, bool can_alloc)
|
||
{
|
||
struct kvfree_rcu_bulk_data *bnode;
|
||
int idx;
|
||
|
||
*krcp = krc_this_cpu_lock(flags);
|
||
if (unlikely(!(*krcp)->initialized))
|
||
return false;
|
||
|
||
idx = !!is_vmalloc_addr(ptr);
|
||
bnode = list_first_entry_or_null(&(*krcp)->bulk_head[idx],
|
||
struct kvfree_rcu_bulk_data, list);
|
||
|
||
/* Check if a new block is required. */
|
||
if (!bnode || bnode->nr_records == KVFREE_BULK_MAX_ENTR) {
|
||
bnode = get_cached_bnode(*krcp);
|
||
if (!bnode && can_alloc) {
|
||
krc_this_cpu_unlock(*krcp, *flags);
|
||
|
||
// __GFP_NORETRY - allows a light-weight direct reclaim
|
||
// what is OK from minimizing of fallback hitting point of
|
||
// view. Apart of that it forbids any OOM invoking what is
|
||
// also beneficial since we are about to release memory soon.
|
||
//
|
||
// __GFP_NOMEMALLOC - prevents from consuming of all the
|
||
// memory reserves. Please note we have a fallback path.
|
||
//
|
||
// __GFP_NOWARN - it is supposed that an allocation can
|
||
// be failed under low memory or high memory pressure
|
||
// scenarios.
|
||
bnode = (struct kvfree_rcu_bulk_data *)
|
||
__get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
|
||
raw_spin_lock_irqsave(&(*krcp)->lock, *flags);
|
||
}
|
||
|
||
if (!bnode)
|
||
return false;
|
||
|
||
// Initialize the new block and attach it.
|
||
bnode->nr_records = 0;
|
||
list_add(&bnode->list, &(*krcp)->bulk_head[idx]);
|
||
}
|
||
|
||
// Finally insert and update the GP for this page.
|
||
bnode->nr_records++;
|
||
bnode->records[bnode->nr_records - 1] = ptr;
|
||
get_state_synchronize_rcu_full(&bnode->gp_snap);
|
||
atomic_inc(&(*krcp)->bulk_count[idx]);
|
||
|
||
return true;
|
||
}
|
||
|
||
/*
|
||
* Queue a request for lazy invocation of the appropriate free routine
|
||
* after a grace period. Please note that three paths are maintained,
|
||
* two for the common case using arrays of pointers and a third one that
|
||
* is used only when the main paths cannot be used, for example, due to
|
||
* memory pressure.
|
||
*
|
||
* Each kvfree_call_rcu() request is added to a batch. The batch will be drained
|
||
* every KFREE_DRAIN_JIFFIES number of jiffies. All the objects in the batch will
|
||
* be free'd in workqueue context. This allows us to: batch requests together to
|
||
* reduce the number of grace periods during heavy kfree_rcu()/kvfree_rcu() load.
|
||
*/
|
||
void kvfree_call_rcu(struct rcu_head *head, void *ptr)
|
||
{
|
||
unsigned long flags;
|
||
struct kfree_rcu_cpu *krcp;
|
||
bool success;
|
||
|
||
/*
|
||
* Please note there is a limitation for the head-less
|
||
* variant, that is why there is a clear rule for such
|
||
* objects: it can be used from might_sleep() context
|
||
* only. For other places please embed an rcu_head to
|
||
* your data.
|
||
*/
|
||
if (!head)
|
||
might_sleep();
|
||
|
||
// Queue the object but don't yet schedule the batch.
|
||
if (debug_rcu_head_queue(ptr)) {
|
||
// Probable double kfree_rcu(), just leak.
|
||
WARN_ONCE(1, "%s(): Double-freed call. rcu_head %p\n",
|
||
__func__, head);
|
||
|
||
// Mark as success and leave.
|
||
return;
|
||
}
|
||
|
||
kasan_record_aux_stack_noalloc(ptr);
|
||
success = add_ptr_to_bulk_krc_lock(&krcp, &flags, ptr, !head);
|
||
if (!success) {
|
||
run_page_cache_worker(krcp);
|
||
|
||
if (head == NULL)
|
||
// Inline if kvfree_rcu(one_arg) call.
|
||
goto unlock_return;
|
||
|
||
head->func = ptr;
|
||
head->next = krcp->head;
|
||
WRITE_ONCE(krcp->head, head);
|
||
atomic_inc(&krcp->head_count);
|
||
|
||
// Take a snapshot for this krcp.
|
||
krcp->head_gp_snap = get_state_synchronize_rcu();
|
||
success = true;
|
||
}
|
||
|
||
/*
|
||
* The kvfree_rcu() caller considers the pointer freed at this point
|
||
* and likely removes any references to it. Since the actual slab
|
||
* freeing (and kmemleak_free()) is deferred, tell kmemleak to ignore
|
||
* this object (no scanning or false positives reporting).
|
||
*/
|
||
kmemleak_ignore(ptr);
|
||
|
||
// Set timer to drain after KFREE_DRAIN_JIFFIES.
|
||
if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING)
|
||
schedule_delayed_monitor_work(krcp);
|
||
|
||
unlock_return:
|
||
krc_this_cpu_unlock(krcp, flags);
|
||
|
||
/*
|
||
* Inline kvfree() after synchronize_rcu(). We can do
|
||
* it from might_sleep() context only, so the current
|
||
* CPU can pass the QS state.
|
||
*/
|
||
if (!success) {
|
||
debug_rcu_head_unqueue((struct rcu_head *) ptr);
|
||
synchronize_rcu();
|
||
kvfree(ptr);
|
||
}
|
||
}
|
||
EXPORT_SYMBOL_GPL(kvfree_call_rcu);
|
||
|
||
/**
|
||
* kvfree_rcu_barrier - Wait until all in-flight kvfree_rcu() complete.
|
||
*
|
||
* Note that a single argument of kvfree_rcu() call has a slow path that
|
||
* triggers synchronize_rcu() following by freeing a pointer. It is done
|
||
* before the return from the function. Therefore for any single-argument
|
||
* call that will result in a kfree() to a cache that is to be destroyed
|
||
* during module exit, it is developer's responsibility to ensure that all
|
||
* such calls have returned before the call to kmem_cache_destroy().
|
||
*/
|
||
void kvfree_rcu_barrier(void)
|
||
{
|
||
struct kfree_rcu_cpu_work *krwp;
|
||
struct kfree_rcu_cpu *krcp;
|
||
bool queued;
|
||
int i, cpu;
|
||
|
||
/*
|
||
* Firstly we detach objects and queue them over an RCU-batch
|
||
* for all CPUs. Finally queued works are flushed for each CPU.
|
||
*
|
||
* Please note. If there are outstanding batches for a particular
|
||
* CPU, those have to be finished first following by queuing a new.
|
||
*/
|
||
for_each_possible_cpu(cpu) {
|
||
krcp = per_cpu_ptr(&krc, cpu);
|
||
|
||
/*
|
||
* Check if this CPU has any objects which have been queued for a
|
||
* new GP completion. If not(means nothing to detach), we are done
|
||
* with it. If any batch is pending/running for this "krcp", below
|
||
* per-cpu flush_rcu_work() waits its completion(see last step).
|
||
*/
|
||
if (!need_offload_krc(krcp))
|
||
continue;
|
||
|
||
while (1) {
|
||
/*
|
||
* If we are not able to queue a new RCU work it means:
|
||
* - batches for this CPU are still in flight which should
|
||
* be flushed first and then repeat;
|
||
* - no objects to detach, because of concurrency.
|
||
*/
|
||
queued = kvfree_rcu_queue_batch(krcp);
|
||
|
||
/*
|
||
* Bail out, if there is no need to offload this "krcp"
|
||
* anymore. As noted earlier it can run concurrently.
|
||
*/
|
||
if (queued || !need_offload_krc(krcp))
|
||
break;
|
||
|
||
/* There are ongoing batches. */
|
||
for (i = 0; i < KFREE_N_BATCHES; i++) {
|
||
krwp = &(krcp->krw_arr[i]);
|
||
flush_rcu_work(&krwp->rcu_work);
|
||
}
|
||
}
|
||
}
|
||
|
||
/*
|
||
* Now we guarantee that all objects are flushed.
|
||
*/
|
||
for_each_possible_cpu(cpu) {
|
||
krcp = per_cpu_ptr(&krc, cpu);
|
||
|
||
/*
|
||
* A monitor work can drain ready to reclaim objects
|
||
* directly. Wait its completion if running or pending.
|
||
*/
|
||
cancel_delayed_work_sync(&krcp->monitor_work);
|
||
|
||
for (i = 0; i < KFREE_N_BATCHES; i++) {
|
||
krwp = &(krcp->krw_arr[i]);
|
||
flush_rcu_work(&krwp->rcu_work);
|
||
}
|
||
}
|
||
}
|
||
EXPORT_SYMBOL_GPL(kvfree_rcu_barrier);
|
||
|
||
static unsigned long
|
||
kfree_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
|
||
{
|
||
int cpu;
|
||
unsigned long count = 0;
|
||
|
||
/* Snapshot count of all CPUs */
|
||
for_each_possible_cpu(cpu) {
|
||
struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
|
||
|
||
count += krc_count(krcp);
|
||
count += READ_ONCE(krcp->nr_bkv_objs);
|
||
atomic_set(&krcp->backoff_page_cache_fill, 1);
|
||
}
|
||
|
||
return count == 0 ? SHRINK_EMPTY : count;
|
||
}
|
||
|
||
static unsigned long
|
||
kfree_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
|
||
{
|
||
int cpu, freed = 0;
|
||
|
||
for_each_possible_cpu(cpu) {
|
||
int count;
|
||
struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
|
||
|
||
count = krc_count(krcp);
|
||
count += drain_page_cache(krcp);
|
||
kfree_rcu_monitor(&krcp->monitor_work.work);
|
||
|
||
sc->nr_to_scan -= count;
|
||
freed += count;
|
||
|
||
if (sc->nr_to_scan <= 0)
|
||
break;
|
||
}
|
||
|
||
return freed == 0 ? SHRINK_STOP : freed;
|
||
}
|
||
|
||
void __init kfree_rcu_scheduler_running(void)
|
||
{
|
||
int cpu;
|
||
|
||
for_each_possible_cpu(cpu) {
|
||
struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
|
||
|
||
if (need_offload_krc(krcp))
|
||
schedule_delayed_monitor_work(krcp);
|
||
}
|
||
}
|
||
|
||
/*
|
||
* During early boot, any blocking grace-period wait automatically
|
||
* implies a grace period.
|
||
*
|
||
* Later on, this could in theory be the case for kernels built with
|
||
* CONFIG_SMP=y && CONFIG_PREEMPTION=y running on a single CPU, but this
|
||
* is not a common case. Furthermore, this optimization would cause
|
||
* the rcu_gp_oldstate structure to expand by 50%, so this potential
|
||
* grace-period optimization is ignored once the scheduler is running.
|
||
*/
|
||
static int rcu_blocking_is_gp(void)
|
||
{
|
||
if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE) {
|
||
might_sleep();
|
||
return false;
|
||
}
|
||
return true;
|
||
}
|
||
|
||
/*
|
||
* Helper function for the synchronize_rcu() API.
|
||
*/
|
||
static void synchronize_rcu_normal(void)
|
||
{
|
||
struct rcu_synchronize rs;
|
||
|
||
trace_rcu_sr_normal(rcu_state.name, &rs.head, TPS("request"));
|
||
|
||
if (!READ_ONCE(rcu_normal_wake_from_gp)) {
|
||
wait_rcu_gp(call_rcu_hurry);
|
||
goto trace_complete_out;
|
||
}
|
||
|
||
init_rcu_head_on_stack(&rs.head);
|
||
init_completion(&rs.completion);
|
||
|
||
/*
|
||
* This code might be preempted, therefore take a GP
|
||
* snapshot before adding a request.
|
||
*/
|
||
if (IS_ENABLED(CONFIG_PROVE_RCU))
|
||
rs.head.func = (void *) get_state_synchronize_rcu();
|
||
|
||
rcu_sr_normal_add_req(&rs);
|
||
|
||
/* Kick a GP and start waiting. */
|
||
(void) start_poll_synchronize_rcu();
|
||
|
||
/* Now we can wait. */
|
||
wait_for_completion(&rs.completion);
|
||
destroy_rcu_head_on_stack(&rs.head);
|
||
|
||
trace_complete_out:
|
||
trace_rcu_sr_normal(rcu_state.name, &rs.head, TPS("complete"));
|
||
}
|
||
|
||
/**
|
||
* synchronize_rcu - wait until a grace period has elapsed.
|
||
*
|
||
* Control will return to the caller some time after a full grace
|
||
* period has elapsed, in other words after all currently executing RCU
|
||
* read-side critical sections have completed. Note, however, that
|
||
* upon return from synchronize_rcu(), the caller might well be executing
|
||
* concurrently with new RCU read-side critical sections that began while
|
||
* synchronize_rcu() was waiting.
|
||
*
|
||
* RCU read-side critical sections are delimited by rcu_read_lock()
|
||
* and rcu_read_unlock(), and may be nested. In addition, but only in
|
||
* v5.0 and later, regions of code across which interrupts, preemption,
|
||
* or softirqs have been disabled also serve as RCU read-side critical
|
||
* sections. This includes hardware interrupt handlers, softirq handlers,
|
||
* and NMI handlers.
|
||
*
|
||
* Note that this guarantee implies further memory-ordering guarantees.
|
||
* On systems with more than one CPU, when synchronize_rcu() returns,
|
||
* each CPU is guaranteed to have executed a full memory barrier since
|
||
* the end of its last RCU read-side critical section whose beginning
|
||
* preceded the call to synchronize_rcu(). In addition, each CPU having
|
||
* an RCU read-side critical section that extends beyond the return from
|
||
* synchronize_rcu() is guaranteed to have executed a full memory barrier
|
||
* after the beginning of synchronize_rcu() and before the beginning of
|
||
* that RCU read-side critical section. Note that these guarantees include
|
||
* CPUs that are offline, idle, or executing in user mode, as well as CPUs
|
||
* that are executing in the kernel.
|
||
*
|
||
* Furthermore, if CPU A invoked synchronize_rcu(), which returned
|
||
* to its caller on CPU B, then both CPU A and CPU B are guaranteed
|
||
* to have executed a full memory barrier during the execution of
|
||
* synchronize_rcu() -- even if CPU A and CPU B are the same CPU (but
|
||
* again only if the system has more than one CPU).
|
||
*
|
||
* Implementation of these memory-ordering guarantees is described here:
|
||
* Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
|
||
*/
|
||
void synchronize_rcu(void)
|
||
{
|
||
unsigned long flags;
|
||
struct rcu_node *rnp;
|
||
|
||
RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
|
||
lock_is_held(&rcu_lock_map) ||
|
||
lock_is_held(&rcu_sched_lock_map),
|
||
"Illegal synchronize_rcu() in RCU read-side critical section");
|
||
if (!rcu_blocking_is_gp()) {
|
||
if (rcu_gp_is_expedited())
|
||
synchronize_rcu_expedited();
|
||
else
|
||
synchronize_rcu_normal();
|
||
return;
|
||
}
|
||
|
||
// Context allows vacuous grace periods.
|
||
// Note well that this code runs with !PREEMPT && !SMP.
|
||
// In addition, all code that advances grace periods runs at
|
||
// process level. Therefore, this normal GP overlaps with other
|
||
// normal GPs only by being fully nested within them, which allows
|
||
// reuse of ->gp_seq_polled_snap.
|
||
rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_snap);
|
||
rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_snap);
|
||
|
||
// Update the normal grace-period counters to record
|
||
// this grace period, but only those used by the boot CPU.
|
||
// The rcu_scheduler_starting() will take care of the rest of
|
||
// these counters.
|
||
local_irq_save(flags);
|
||
WARN_ON_ONCE(num_online_cpus() > 1);
|
||
rcu_state.gp_seq += (1 << RCU_SEQ_CTR_SHIFT);
|
||
for (rnp = this_cpu_ptr(&rcu_data)->mynode; rnp; rnp = rnp->parent)
|
||
rnp->gp_seq_needed = rnp->gp_seq = rcu_state.gp_seq;
|
||
local_irq_restore(flags);
|
||
}
|
||
EXPORT_SYMBOL_GPL(synchronize_rcu);
|
||
|
||
/**
|
||
* get_completed_synchronize_rcu_full - Return a full pre-completed polled state cookie
|
||
* @rgosp: Place to put state cookie
|
||
*
|
||
* Stores into @rgosp a value that will always be treated by functions
|
||
* like poll_state_synchronize_rcu_full() as a cookie whose grace period
|
||
* has already completed.
|
||
*/
|
||
void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
|
||
{
|
||
rgosp->rgos_norm = RCU_GET_STATE_COMPLETED;
|
||
rgosp->rgos_exp = RCU_GET_STATE_COMPLETED;
|
||
}
|
||
EXPORT_SYMBOL_GPL(get_completed_synchronize_rcu_full);
|
||
|
||
/**
|
||
* get_state_synchronize_rcu - Snapshot current RCU state
|
||
*
|
||
* Returns a cookie that is used by a later call to cond_synchronize_rcu()
|
||
* or poll_state_synchronize_rcu() to determine whether or not a full
|
||
* grace period has elapsed in the meantime.
|
||
*/
|
||
unsigned long get_state_synchronize_rcu(void)
|
||
{
|
||
/*
|
||
* Any prior manipulation of RCU-protected data must happen
|
||
* before the load from ->gp_seq.
|
||
*/
|
||
smp_mb(); /* ^^^ */
|
||
return rcu_seq_snap(&rcu_state.gp_seq_polled);
|
||
}
|
||
EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
|
||
|
||
/**
|
||
* get_state_synchronize_rcu_full - Snapshot RCU state, both normal and expedited
|
||
* @rgosp: location to place combined normal/expedited grace-period state
|
||
*
|
||
* Places the normal and expedited grace-period states in @rgosp. This
|
||
* state value can be passed to a later call to cond_synchronize_rcu_full()
|
||
* or poll_state_synchronize_rcu_full() to determine whether or not a
|
||
* grace period (whether normal or expedited) has elapsed in the meantime.
|
||
* The rcu_gp_oldstate structure takes up twice the memory of an unsigned
|
||
* long, but is guaranteed to see all grace periods. In contrast, the
|
||
* combined state occupies less memory, but can sometimes fail to take
|
||
* grace periods into account.
|
||
*
|
||
* This does not guarantee that the needed grace period will actually
|
||
* start.
|
||
*/
|
||
void get_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
|
||
{
|
||
struct rcu_node *rnp = rcu_get_root();
|
||
|
||
/*
|
||
* Any prior manipulation of RCU-protected data must happen
|
||
* before the loads from ->gp_seq and ->expedited_sequence.
|
||
*/
|
||
smp_mb(); /* ^^^ */
|
||
rgosp->rgos_norm = rcu_seq_snap(&rnp->gp_seq);
|
||
rgosp->rgos_exp = rcu_seq_snap(&rcu_state.expedited_sequence);
|
||
}
|
||
EXPORT_SYMBOL_GPL(get_state_synchronize_rcu_full);
|
||
|
||
/*
|
||
* Helper function for start_poll_synchronize_rcu() and
|
||
* start_poll_synchronize_rcu_full().
|
||
*/
|
||
static void start_poll_synchronize_rcu_common(void)
|
||
{
|
||
unsigned long flags;
|
||
bool needwake;
|
||
struct rcu_data *rdp;
|
||
struct rcu_node *rnp;
|
||
|
||
lockdep_assert_irqs_enabled();
|
||
local_irq_save(flags);
|
||
rdp = this_cpu_ptr(&rcu_data);
|
||
rnp = rdp->mynode;
|
||
raw_spin_lock_rcu_node(rnp); // irqs already disabled.
|
||
// Note it is possible for a grace period to have elapsed between
|
||
// the above call to get_state_synchronize_rcu() and the below call
|
||
// to rcu_seq_snap. This is OK, the worst that happens is that we
|
||
// get a grace period that no one needed. These accesses are ordered
|
||
// by smp_mb(), and we are accessing them in the opposite order
|
||
// from which they are updated at grace-period start, as required.
|
||
needwake = rcu_start_this_gp(rnp, rdp, rcu_seq_snap(&rcu_state.gp_seq));
|
||
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
||
if (needwake)
|
||
rcu_gp_kthread_wake();
|
||
}
|
||
|
||
/**
|
||
* start_poll_synchronize_rcu - Snapshot and start RCU grace period
|
||
*
|
||
* Returns a cookie that is used by a later call to cond_synchronize_rcu()
|
||
* or poll_state_synchronize_rcu() to determine whether or not a full
|
||
* grace period has elapsed in the meantime. If the needed grace period
|
||
* is not already slated to start, notifies RCU core of the need for that
|
||
* grace period.
|
||
*
|
||
* Interrupts must be enabled for the case where it is necessary to awaken
|
||
* the grace-period kthread.
|
||
*/
|
||
unsigned long start_poll_synchronize_rcu(void)
|
||
{
|
||
unsigned long gp_seq = get_state_synchronize_rcu();
|
||
|
||
start_poll_synchronize_rcu_common();
|
||
return gp_seq;
|
||
}
|
||
EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu);
|
||
|
||
/**
|
||
* start_poll_synchronize_rcu_full - Take a full snapshot and start RCU grace period
|
||
* @rgosp: value from get_state_synchronize_rcu_full() or start_poll_synchronize_rcu_full()
|
||
*
|
||
* Places the normal and expedited grace-period states in *@rgos. This
|
||
* state value can be passed to a later call to cond_synchronize_rcu_full()
|
||
* or poll_state_synchronize_rcu_full() to determine whether or not a
|
||
* grace period (whether normal or expedited) has elapsed in the meantime.
|
||
* If the needed grace period is not already slated to start, notifies
|
||
* RCU core of the need for that grace period.
|
||
*
|
||
* Interrupts must be enabled for the case where it is necessary to awaken
|
||
* the grace-period kthread.
|
||
*/
|
||
void start_poll_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
|
||
{
|
||
get_state_synchronize_rcu_full(rgosp);
|
||
|
||
start_poll_synchronize_rcu_common();
|
||
}
|
||
EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_full);
|
||
|
||
/**
|
||
* poll_state_synchronize_rcu - Has the specified RCU grace period completed?
|
||
* @oldstate: value from get_state_synchronize_rcu() or start_poll_synchronize_rcu()
|
||
*
|
||
* If a full RCU grace period has elapsed since the earlier call from
|
||
* which @oldstate was obtained, return @true, otherwise return @false.
|
||
* If @false is returned, it is the caller's responsibility to invoke this
|
||
* function later on until it does return @true. Alternatively, the caller
|
||
* can explicitly wait for a grace period, for example, by passing @oldstate
|
||
* to either cond_synchronize_rcu() or cond_synchronize_rcu_expedited()
|
||
* on the one hand or by directly invoking either synchronize_rcu() or
|
||
* synchronize_rcu_expedited() on the other.
|
||
*
|
||
* Yes, this function does not take counter wrap into account.
|
||
* But counter wrap is harmless. If the counter wraps, we have waited for
|
||
* more than a billion grace periods (and way more on a 64-bit system!).
|
||
* Those needing to keep old state values for very long time periods
|
||
* (many hours even on 32-bit systems) should check them occasionally and
|
||
* either refresh them or set a flag indicating that the grace period has
|
||
* completed. Alternatively, they can use get_completed_synchronize_rcu()
|
||
* to get a guaranteed-completed grace-period state.
|
||
*
|
||
* In addition, because oldstate compresses the grace-period state for
|
||
* both normal and expedited grace periods into a single unsigned long,
|
||
* it can miss a grace period when synchronize_rcu() runs concurrently
|
||
* with synchronize_rcu_expedited(). If this is unacceptable, please
|
||
* instead use the _full() variant of these polling APIs.
|
||
*
|
||
* This function provides the same memory-ordering guarantees that
|
||
* would be provided by a synchronize_rcu() that was invoked at the call
|
||
* to the function that provided @oldstate, and that returned at the end
|
||
* of this function.
|
||
*/
|
||
bool poll_state_synchronize_rcu(unsigned long oldstate)
|
||
{
|
||
if (oldstate == RCU_GET_STATE_COMPLETED ||
|
||
rcu_seq_done_exact(&rcu_state.gp_seq_polled, oldstate)) {
|
||
smp_mb(); /* Ensure GP ends before subsequent accesses. */
|
||
return true;
|
||
}
|
||
return false;
|
||
}
|
||
EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
|
||
|
||
/**
|
||
* poll_state_synchronize_rcu_full - Has the specified RCU grace period completed?
|
||
* @rgosp: value from get_state_synchronize_rcu_full() or start_poll_synchronize_rcu_full()
|
||
*
|
||
* If a full RCU grace period has elapsed since the earlier call from
|
||
* which *rgosp was obtained, return @true, otherwise return @false.
|
||
* If @false is returned, it is the caller's responsibility to invoke this
|
||
* function later on until it does return @true. Alternatively, the caller
|
||
* can explicitly wait for a grace period, for example, by passing @rgosp
|
||
* to cond_synchronize_rcu() or by directly invoking synchronize_rcu().
|
||
*
|
||
* Yes, this function does not take counter wrap into account.
|
||
* But counter wrap is harmless. If the counter wraps, we have waited
|
||
* for more than a billion grace periods (and way more on a 64-bit
|
||
* system!). Those needing to keep rcu_gp_oldstate values for very
|
||
* long time periods (many hours even on 32-bit systems) should check
|
||
* them occasionally and either refresh them or set a flag indicating
|
||
* that the grace period has completed. Alternatively, they can use
|
||
* get_completed_synchronize_rcu_full() to get a guaranteed-completed
|
||
* grace-period state.
|
||
*
|
||
* This function provides the same memory-ordering guarantees that would
|
||
* be provided by a synchronize_rcu() that was invoked at the call to
|
||
* the function that provided @rgosp, and that returned at the end of this
|
||
* function. And this guarantee requires that the root rcu_node structure's
|
||
* ->gp_seq field be checked instead of that of the rcu_state structure.
|
||
* The problem is that the just-ending grace-period's callbacks can be
|
||
* invoked between the time that the root rcu_node structure's ->gp_seq
|
||
* field is updated and the time that the rcu_state structure's ->gp_seq
|
||
* field is updated. Therefore, if a single synchronize_rcu() is to
|
||
* cause a subsequent poll_state_synchronize_rcu_full() to return @true,
|
||
* then the root rcu_node structure is the one that needs to be polled.
|
||
*/
|
||
bool poll_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
|
||
{
|
||
struct rcu_node *rnp = rcu_get_root();
|
||
|
||
smp_mb(); // Order against root rcu_node structure grace-period cleanup.
|
||
if (rgosp->rgos_norm == RCU_GET_STATE_COMPLETED ||
|
||
rcu_seq_done_exact(&rnp->gp_seq, rgosp->rgos_norm) ||
|
||
rgosp->rgos_exp == RCU_GET_STATE_COMPLETED ||
|
||
rcu_seq_done_exact(&rcu_state.expedited_sequence, rgosp->rgos_exp)) {
|
||
smp_mb(); /* Ensure GP ends before subsequent accesses. */
|
||
return true;
|
||
}
|
||
return false;
|
||
}
|
||
EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu_full);
|
||
|
||
/**
|
||
* cond_synchronize_rcu - Conditionally wait for an RCU grace period
|
||
* @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited()
|
||
*
|
||
* If a full RCU grace period has elapsed since the earlier call to
|
||
* get_state_synchronize_rcu() or start_poll_synchronize_rcu(), just return.
|
||
* Otherwise, invoke synchronize_rcu() to wait for a full grace period.
|
||
*
|
||
* Yes, this function does not take counter wrap into account.
|
||
* But counter wrap is harmless. If the counter wraps, we have waited for
|
||
* more than 2 billion grace periods (and way more on a 64-bit system!),
|
||
* so waiting for a couple of additional grace periods should be just fine.
|
||
*
|
||
* This function provides the same memory-ordering guarantees that
|
||
* would be provided by a synchronize_rcu() that was invoked at the call
|
||
* to the function that provided @oldstate and that returned at the end
|
||
* of this function.
|
||
*/
|
||
void cond_synchronize_rcu(unsigned long oldstate)
|
||
{
|
||
if (!poll_state_synchronize_rcu(oldstate))
|
||
synchronize_rcu();
|
||
}
|
||
EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
|
||
|
||
/**
|
||
* cond_synchronize_rcu_full - Conditionally wait for an RCU grace period
|
||
* @rgosp: value from get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), or start_poll_synchronize_rcu_expedited_full()
|
||
*
|
||
* If a full RCU grace period has elapsed since the call to
|
||
* get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(),
|
||
* or start_poll_synchronize_rcu_expedited_full() from which @rgosp was
|
||
* obtained, just return. Otherwise, invoke synchronize_rcu() to wait
|
||
* for a full grace period.
|
||
*
|
||
* Yes, this function does not take counter wrap into account.
|
||
* But counter wrap is harmless. If the counter wraps, we have waited for
|
||
* more than 2 billion grace periods (and way more on a 64-bit system!),
|
||
* so waiting for a couple of additional grace periods should be just fine.
|
||
*
|
||
* This function provides the same memory-ordering guarantees that
|
||
* would be provided by a synchronize_rcu() that was invoked at the call
|
||
* to the function that provided @rgosp and that returned at the end of
|
||
* this function.
|
||
*/
|
||
void cond_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
|
||
{
|
||
if (!poll_state_synchronize_rcu_full(rgosp))
|
||
synchronize_rcu();
|
||
}
|
||
EXPORT_SYMBOL_GPL(cond_synchronize_rcu_full);
|
||
|
||
/*
|
||
* Check to see if there is any immediate RCU-related work to be done by
|
||
* the current CPU, returning 1 if so and zero otherwise. The checks are
|
||
* in order of increasing expense: checks that can be carried out against
|
||
* CPU-local state are performed first. However, we must check for CPU
|
||
* stalls first, else we might not get a chance.
|
||
*/
|
||
static int rcu_pending(int user)
|
||
{
|
||
bool gp_in_progress;
|
||
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
|
||
struct rcu_node *rnp = rdp->mynode;
|
||
|
||
lockdep_assert_irqs_disabled();
|
||
|
||
/* Check for CPU stalls, if enabled. */
|
||
check_cpu_stall(rdp);
|
||
|
||
/* Does this CPU need a deferred NOCB wakeup? */
|
||
if (rcu_nocb_need_deferred_wakeup(rdp, RCU_NOCB_WAKE))
|
||
return 1;
|
||
|
||
/* Is this a nohz_full CPU in userspace or idle? (Ignore RCU if so.) */
|
||
gp_in_progress = rcu_gp_in_progress();
|
||
if ((user || rcu_is_cpu_rrupt_from_idle() ||
|
||
(gp_in_progress &&
|
||
time_before(jiffies, READ_ONCE(rcu_state.gp_start) +
|
||
nohz_full_patience_delay_jiffies))) &&
|
||
rcu_nohz_full_cpu())
|
||
return 0;
|
||
|
||
/* Is the RCU core waiting for a quiescent state from this CPU? */
|
||
if (rdp->core_needs_qs && !rdp->cpu_no_qs.b.norm && gp_in_progress)
|
||
return 1;
|
||
|
||
/* Does this CPU have callbacks ready to invoke? */
|
||
if (!rcu_rdp_is_offloaded(rdp) &&
|
||
rcu_segcblist_ready_cbs(&rdp->cblist))
|
||
return 1;
|
||
|
||
/* Has RCU gone idle with this CPU needing another grace period? */
|
||
if (!gp_in_progress && rcu_segcblist_is_enabled(&rdp->cblist) &&
|
||
!rcu_rdp_is_offloaded(rdp) &&
|
||
!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
|
||
return 1;
|
||
|
||
/* Have RCU grace period completed or started? */
|
||
if (rcu_seq_current(&rnp->gp_seq) != rdp->gp_seq ||
|
||
unlikely(READ_ONCE(rdp->gpwrap))) /* outside lock */
|
||
return 1;
|
||
|
||
/* nothing to do */
|
||
return 0;
|
||
}
|
||
|
||
/*
|
||
* Helper function for rcu_barrier() tracing. If tracing is disabled,
|
||
* the compiler is expected to optimize this away.
|
||
*/
|
||
static void rcu_barrier_trace(const char *s, int cpu, unsigned long done)
|
||
{
|
||
trace_rcu_barrier(rcu_state.name, s, cpu,
|
||
atomic_read(&rcu_state.barrier_cpu_count), done);
|
||
}
|
||
|
||
/*
|
||
* RCU callback function for rcu_barrier(). If we are last, wake
|
||
* up the task executing rcu_barrier().
|
||
*
|
||
* Note that the value of rcu_state.barrier_sequence must be captured
|
||
* before the atomic_dec_and_test(). Otherwise, if this CPU is not last,
|
||
* other CPUs might count the value down to zero before this CPU gets
|
||
* around to invoking rcu_barrier_trace(), which might result in bogus
|
||
* data from the next instance of rcu_barrier().
|
||
*/
|
||
static void rcu_barrier_callback(struct rcu_head *rhp)
|
||
{
|
||
unsigned long __maybe_unused s = rcu_state.barrier_sequence;
|
||
|
||
rhp->next = rhp; // Mark the callback as having been invoked.
|
||
if (atomic_dec_and_test(&rcu_state.barrier_cpu_count)) {
|
||
rcu_barrier_trace(TPS("LastCB"), -1, s);
|
||
complete(&rcu_state.barrier_completion);
|
||
} else {
|
||
rcu_barrier_trace(TPS("CB"), -1, s);
|
||
}
|
||
}
|
||
|
||
/*
|
||
* If needed, entrain an rcu_barrier() callback on rdp->cblist.
|
||
*/
|
||
static void rcu_barrier_entrain(struct rcu_data *rdp)
|
||
{
|
||
unsigned long gseq = READ_ONCE(rcu_state.barrier_sequence);
|
||
unsigned long lseq = READ_ONCE(rdp->barrier_seq_snap);
|
||
bool wake_nocb = false;
|
||
bool was_alldone = false;
|
||
|
||
lockdep_assert_held(&rcu_state.barrier_lock);
|
||
if (rcu_seq_state(lseq) || !rcu_seq_state(gseq) || rcu_seq_ctr(lseq) != rcu_seq_ctr(gseq))
|
||
return;
|
||
rcu_barrier_trace(TPS("IRQ"), -1, rcu_state.barrier_sequence);
|
||
rdp->barrier_head.func = rcu_barrier_callback;
|
||
debug_rcu_head_queue(&rdp->barrier_head);
|
||
rcu_nocb_lock(rdp);
|
||
/*
|
||
* Flush bypass and wakeup rcuog if we add callbacks to an empty regular
|
||
* queue. This way we don't wait for bypass timer that can reach seconds
|
||
* if it's fully lazy.
|
||
*/
|
||
was_alldone = rcu_rdp_is_offloaded(rdp) && !rcu_segcblist_pend_cbs(&rdp->cblist);
|
||
WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false));
|
||
wake_nocb = was_alldone && rcu_segcblist_pend_cbs(&rdp->cblist);
|
||
if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head)) {
|
||
atomic_inc(&rcu_state.barrier_cpu_count);
|
||
} else {
|
||
debug_rcu_head_unqueue(&rdp->barrier_head);
|
||
rcu_barrier_trace(TPS("IRQNQ"), -1, rcu_state.barrier_sequence);
|
||
}
|
||
rcu_nocb_unlock(rdp);
|
||
if (wake_nocb)
|
||
wake_nocb_gp(rdp, false);
|
||
smp_store_release(&rdp->barrier_seq_snap, gseq);
|
||
}
|
||
|
||
/*
|
||
* Called with preemption disabled, and from cross-cpu IRQ context.
|
||
*/
|
||
static void rcu_barrier_handler(void *cpu_in)
|
||
{
|
||
uintptr_t cpu = (uintptr_t)cpu_in;
|
||
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
|
||
|
||
lockdep_assert_irqs_disabled();
|
||
WARN_ON_ONCE(cpu != rdp->cpu);
|
||
WARN_ON_ONCE(cpu != smp_processor_id());
|
||
raw_spin_lock(&rcu_state.barrier_lock);
|
||
rcu_barrier_entrain(rdp);
|
||
raw_spin_unlock(&rcu_state.barrier_lock);
|
||
}
|
||
|
||
/**
|
||
* rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
|
||
*
|
||
* Note that this primitive does not necessarily wait for an RCU grace period
|
||
* to complete. For example, if there are no RCU callbacks queued anywhere
|
||
* in the system, then rcu_barrier() is within its rights to return
|
||
* immediately, without waiting for anything, much less an RCU grace period.
|
||
*/
|
||
void rcu_barrier(void)
|
||
{
|
||
uintptr_t cpu;
|
||
unsigned long flags;
|
||
unsigned long gseq;
|
||
struct rcu_data *rdp;
|
||
unsigned long s = rcu_seq_snap(&rcu_state.barrier_sequence);
|
||
|
||
rcu_barrier_trace(TPS("Begin"), -1, s);
|
||
|
||
/* Take mutex to serialize concurrent rcu_barrier() requests. */
|
||
mutex_lock(&rcu_state.barrier_mutex);
|
||
|
||
/* Did someone else do our work for us? */
|
||
if (rcu_seq_done(&rcu_state.barrier_sequence, s)) {
|
||
rcu_barrier_trace(TPS("EarlyExit"), -1, rcu_state.barrier_sequence);
|
||
smp_mb(); /* caller's subsequent code after above check. */
|
||
mutex_unlock(&rcu_state.barrier_mutex);
|
||
return;
|
||
}
|
||
|
||
/* Mark the start of the barrier operation. */
|
||
raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags);
|
||
rcu_seq_start(&rcu_state.barrier_sequence);
|
||
gseq = rcu_state.barrier_sequence;
|
||
rcu_barrier_trace(TPS("Inc1"), -1, rcu_state.barrier_sequence);
|
||
|
||
/*
|
||
* Initialize the count to two rather than to zero in order
|
||
* to avoid a too-soon return to zero in case of an immediate
|
||
* invocation of the just-enqueued callback (or preemption of
|
||
* this task). Exclude CPU-hotplug operations to ensure that no
|
||
* offline non-offloaded CPU has callbacks queued.
|
||
*/
|
||
init_completion(&rcu_state.barrier_completion);
|
||
atomic_set(&rcu_state.barrier_cpu_count, 2);
|
||
raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
|
||
|
||
/*
|
||
* Force each CPU with callbacks to register a new callback.
|
||
* When that callback is invoked, we will know that all of the
|
||
* corresponding CPU's preceding callbacks have been invoked.
|
||
*/
|
||
for_each_possible_cpu(cpu) {
|
||
rdp = per_cpu_ptr(&rcu_data, cpu);
|
||
retry:
|
||
if (smp_load_acquire(&rdp->barrier_seq_snap) == gseq)
|
||
continue;
|
||
raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags);
|
||
if (!rcu_segcblist_n_cbs(&rdp->cblist)) {
|
||
WRITE_ONCE(rdp->barrier_seq_snap, gseq);
|
||
raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
|
||
rcu_barrier_trace(TPS("NQ"), cpu, rcu_state.barrier_sequence);
|
||
continue;
|
||
}
|
||
if (!rcu_rdp_cpu_online(rdp)) {
|
||
rcu_barrier_entrain(rdp);
|
||
WARN_ON_ONCE(READ_ONCE(rdp->barrier_seq_snap) != gseq);
|
||
raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
|
||
rcu_barrier_trace(TPS("OfflineNoCBQ"), cpu, rcu_state.barrier_sequence);
|
||
continue;
|
||
}
|
||
raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
|
||
if (smp_call_function_single(cpu, rcu_barrier_handler, (void *)cpu, 1)) {
|
||
schedule_timeout_uninterruptible(1);
|
||
goto retry;
|
||
}
|
||
WARN_ON_ONCE(READ_ONCE(rdp->barrier_seq_snap) != gseq);
|
||
rcu_barrier_trace(TPS("OnlineQ"), cpu, rcu_state.barrier_sequence);
|
||
}
|
||
|
||
/*
|
||
* Now that we have an rcu_barrier_callback() callback on each
|
||
* CPU, and thus each counted, remove the initial count.
|
||
*/
|
||
if (atomic_sub_and_test(2, &rcu_state.barrier_cpu_count))
|
||
complete(&rcu_state.barrier_completion);
|
||
|
||
/* Wait for all rcu_barrier_callback() callbacks to be invoked. */
|
||
wait_for_completion(&rcu_state.barrier_completion);
|
||
|
||
/* Mark the end of the barrier operation. */
|
||
rcu_barrier_trace(TPS("Inc2"), -1, rcu_state.barrier_sequence);
|
||
rcu_seq_end(&rcu_state.barrier_sequence);
|
||
gseq = rcu_state.barrier_sequence;
|
||
for_each_possible_cpu(cpu) {
|
||
rdp = per_cpu_ptr(&rcu_data, cpu);
|
||
|
||
WRITE_ONCE(rdp->barrier_seq_snap, gseq);
|
||
}
|
||
|
||
/* Other rcu_barrier() invocations can now safely proceed. */
|
||
mutex_unlock(&rcu_state.barrier_mutex);
|
||
}
|
||
EXPORT_SYMBOL_GPL(rcu_barrier);
|
||
|
||
static unsigned long rcu_barrier_last_throttle;
|
||
|
||
/**
|
||
* rcu_barrier_throttled - Do rcu_barrier(), but limit to one per second
|
||
*
|
||
* This can be thought of as guard rails around rcu_barrier() that
|
||
* permits unrestricted userspace use, at least assuming the hardware's
|
||
* try_cmpxchg() is robust. There will be at most one call per second to
|
||
* rcu_barrier() system-wide from use of this function, which means that
|
||
* callers might needlessly wait a second or three.
|
||
*
|
||
* This is intended for use by test suites to avoid OOM by flushing RCU
|
||
* callbacks from the previous test before starting the next. See the
|
||
* rcutree.do_rcu_barrier module parameter for more information.
|
||
*
|
||
* Why not simply make rcu_barrier() more scalable? That might be
|
||
* the eventual endpoint, but let's keep it simple for the time being.
|
||
* Note that the module parameter infrastructure serializes calls to a
|
||
* given .set() function, but should concurrent .set() invocation ever be
|
||
* possible, we are ready!
|
||
*/
|
||
static void rcu_barrier_throttled(void)
|
||
{
|
||
unsigned long j = jiffies;
|
||
unsigned long old = READ_ONCE(rcu_barrier_last_throttle);
|
||
unsigned long s = rcu_seq_snap(&rcu_state.barrier_sequence);
|
||
|
||
while (time_in_range(j, old, old + HZ / 16) ||
|
||
!try_cmpxchg(&rcu_barrier_last_throttle, &old, j)) {
|
||
schedule_timeout_idle(HZ / 16);
|
||
if (rcu_seq_done(&rcu_state.barrier_sequence, s)) {
|
||
smp_mb(); /* caller's subsequent code after above check. */
|
||
return;
|
||
}
|
||
j = jiffies;
|
||
old = READ_ONCE(rcu_barrier_last_throttle);
|
||
}
|
||
rcu_barrier();
|
||
}
|
||
|
||
/*
|
||
* Invoke rcu_barrier_throttled() when a rcutree.do_rcu_barrier
|
||
* request arrives. We insist on a true value to allow for possible
|
||
* future expansion.
|
||
*/
|
||
static int param_set_do_rcu_barrier(const char *val, const struct kernel_param *kp)
|
||
{
|
||
bool b;
|
||
int ret;
|
||
|
||
if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING)
|
||
return -EAGAIN;
|
||
ret = kstrtobool(val, &b);
|
||
if (!ret && b) {
|
||
atomic_inc((atomic_t *)kp->arg);
|
||
rcu_barrier_throttled();
|
||
atomic_dec((atomic_t *)kp->arg);
|
||
}
|
||
return ret;
|
||
}
|
||
|
||
/*
|
||
* Output the number of outstanding rcutree.do_rcu_barrier requests.
|
||
*/
|
||
static int param_get_do_rcu_barrier(char *buffer, const struct kernel_param *kp)
|
||
{
|
||
return sprintf(buffer, "%d\n", atomic_read((atomic_t *)kp->arg));
|
||
}
|
||
|
||
static const struct kernel_param_ops do_rcu_barrier_ops = {
|
||
.set = param_set_do_rcu_barrier,
|
||
.get = param_get_do_rcu_barrier,
|
||
};
|
||
static atomic_t do_rcu_barrier;
|
||
module_param_cb(do_rcu_barrier, &do_rcu_barrier_ops, &do_rcu_barrier, 0644);
|
||
|
||
/*
|
||
* Compute the mask of online CPUs for the specified rcu_node structure.
|
||
* This will not be stable unless the rcu_node structure's ->lock is
|
||
* held, but the bit corresponding to the current CPU will be stable
|
||
* in most contexts.
|
||
*/
|
||
static unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
|
||
{
|
||
return READ_ONCE(rnp->qsmaskinitnext);
|
||
}
|
||
|
||
/*
|
||
* Is the CPU corresponding to the specified rcu_data structure online
|
||
* from RCU's perspective? This perspective is given by that structure's
|
||
* ->qsmaskinitnext field rather than by the global cpu_online_mask.
|
||
*/
|
||
static bool rcu_rdp_cpu_online(struct rcu_data *rdp)
|
||
{
|
||
return !!(rdp->grpmask & rcu_rnp_online_cpus(rdp->mynode));
|
||
}
|
||
|
||
bool rcu_cpu_online(int cpu)
|
||
{
|
||
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
|
||
|
||
return rcu_rdp_cpu_online(rdp);
|
||
}
|
||
|
||
#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
|
||
|
||
/*
|
||
* Is the current CPU online as far as RCU is concerned?
|
||
*
|
||
* Disable preemption to avoid false positives that could otherwise
|
||
* happen due to the current CPU number being sampled, this task being
|
||
* preempted, its old CPU being taken offline, resuming on some other CPU,
|
||
* then determining that its old CPU is now offline.
|
||
*
|
||
* Disable checking if in an NMI handler because we cannot safely
|
||
* report errors from NMI handlers anyway. In addition, it is OK to use
|
||
* RCU on an offline processor during initial boot, hence the check for
|
||
* rcu_scheduler_fully_active.
|
||
*/
|
||
bool rcu_lockdep_current_cpu_online(void)
|
||
{
|
||
struct rcu_data *rdp;
|
||
bool ret = false;
|
||
|
||
if (in_nmi() || !rcu_scheduler_fully_active)
|
||
return true;
|
||
preempt_disable_notrace();
|
||
rdp = this_cpu_ptr(&rcu_data);
|
||
/*
|
||
* Strictly, we care here about the case where the current CPU is
|
||
* in rcutree_report_cpu_starting() and thus has an excuse for rdp->grpmask
|
||
* not being up to date. So arch_spin_is_locked() might have a
|
||
* false positive if it's held by some *other* CPU, but that's
|
||
* OK because that just means a false *negative* on the warning.
|
||
*/
|
||
if (rcu_rdp_cpu_online(rdp) || arch_spin_is_locked(&rcu_state.ofl_lock))
|
||
ret = true;
|
||
preempt_enable_notrace();
|
||
return ret;
|
||
}
|
||
EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
|
||
|
||
#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
|
||
|
||
// Has rcu_init() been invoked? This is used (for example) to determine
|
||
// whether spinlocks may be acquired safely.
|
||
static bool rcu_init_invoked(void)
|
||
{
|
||
return !!READ_ONCE(rcu_state.n_online_cpus);
|
||
}
|
||
|
||
/*
|
||
* All CPUs for the specified rcu_node structure have gone offline,
|
||
* and all tasks that were preempted within an RCU read-side critical
|
||
* section while running on one of those CPUs have since exited their RCU
|
||
* read-side critical section. Some other CPU is reporting this fact with
|
||
* the specified rcu_node structure's ->lock held and interrupts disabled.
|
||
* This function therefore goes up the tree of rcu_node structures,
|
||
* clearing the corresponding bits in the ->qsmaskinit fields. Note that
|
||
* the leaf rcu_node structure's ->qsmaskinit field has already been
|
||
* updated.
|
||
*
|
||
* This function does check that the specified rcu_node structure has
|
||
* all CPUs offline and no blocked tasks, so it is OK to invoke it
|
||
* prematurely. That said, invoking it after the fact will cost you
|
||
* a needless lock acquisition. So once it has done its work, don't
|
||
* invoke it again.
|
||
*/
|
||
static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
|
||
{
|
||
long mask;
|
||
struct rcu_node *rnp = rnp_leaf;
|
||
|
||
raw_lockdep_assert_held_rcu_node(rnp_leaf);
|
||
if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
|
||
WARN_ON_ONCE(rnp_leaf->qsmaskinit) ||
|
||
WARN_ON_ONCE(rcu_preempt_has_tasks(rnp_leaf)))
|
||
return;
|
||
for (;;) {
|
||
mask = rnp->grpmask;
|
||
rnp = rnp->parent;
|
||
if (!rnp)
|
||
break;
|
||
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
|
||
rnp->qsmaskinit &= ~mask;
|
||
/* Between grace periods, so better already be zero! */
|
||
WARN_ON_ONCE(rnp->qsmask);
|
||
if (rnp->qsmaskinit) {
|
||
raw_spin_unlock_rcu_node(rnp);
|
||
/* irqs remain disabled. */
|
||
return;
|
||
}
|
||
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
|
||
}
|
||
}
|
||
|
||
/*
|
||
* Propagate ->qsinitmask bits up the rcu_node tree to account for the
|
||
* first CPU in a given leaf rcu_node structure coming online. The caller
|
||
* must hold the corresponding leaf rcu_node ->lock with interrupts
|
||
* disabled.
|
||
*/
|
||
static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
|
||
{
|
||
long mask;
|
||
long oldmask;
|
||
struct rcu_node *rnp = rnp_leaf;
|
||
|
||
raw_lockdep_assert_held_rcu_node(rnp_leaf);
|
||
WARN_ON_ONCE(rnp->wait_blkd_tasks);
|
||
for (;;) {
|
||
mask = rnp->grpmask;
|
||
rnp = rnp->parent;
|
||
if (rnp == NULL)
|
||
return;
|
||
raw_spin_lock_rcu_node(rnp); /* Interrupts already disabled. */
|
||
oldmask = rnp->qsmaskinit;
|
||
rnp->qsmaskinit |= mask;
|
||
raw_spin_unlock_rcu_node(rnp); /* Interrupts remain disabled. */
|
||
if (oldmask)
|
||
return;
|
||
}
|
||
}
|
||
|
||
/*
|
||
* Do boot-time initialization of a CPU's per-CPU RCU data.
|
||
*/
|
||
static void __init
|
||
rcu_boot_init_percpu_data(int cpu)
|
||
{
|
||
struct context_tracking *ct = this_cpu_ptr(&context_tracking);
|
||
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
|
||
|
||
/* Set up local state, ensuring consistent view of global state. */
|
||
rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
|
||
INIT_WORK(&rdp->strict_work, strict_work_handler);
|
||
WARN_ON_ONCE(ct->nesting != 1);
|
||
WARN_ON_ONCE(rcu_watching_snap_in_eqs(ct_rcu_watching_cpu(cpu)));
|
||
rdp->barrier_seq_snap = rcu_state.barrier_sequence;
|
||
rdp->rcu_ofl_gp_seq = rcu_state.gp_seq;
|
||
rdp->rcu_ofl_gp_state = RCU_GP_CLEANED;
|
||
rdp->rcu_onl_gp_seq = rcu_state.gp_seq;
|
||
rdp->rcu_onl_gp_state = RCU_GP_CLEANED;
|
||
rdp->last_sched_clock = jiffies;
|
||
rdp->cpu = cpu;
|
||
rcu_boot_init_nocb_percpu_data(rdp);
|
||
}
|
||
|
||
struct kthread_worker *rcu_exp_gp_kworker;
|
||
|
||
static void rcu_spawn_exp_par_gp_kworker(struct rcu_node *rnp)
|
||
{
|
||
struct kthread_worker *kworker;
|
||
const char *name = "rcu_exp_par_gp_kthread_worker/%d";
|
||
struct sched_param param = { .sched_priority = kthread_prio };
|
||
int rnp_index = rnp - rcu_get_root();
|
||
|
||
if (rnp->exp_kworker)
|
||
return;
|
||
|
||
kworker = kthread_create_worker(0, name, rnp_index);
|
||
if (IS_ERR_OR_NULL(kworker)) {
|
||
pr_err("Failed to create par gp kworker on %d/%d\n",
|
||
rnp->grplo, rnp->grphi);
|
||
return;
|
||
}
|
||
WRITE_ONCE(rnp->exp_kworker, kworker);
|
||
|
||
if (IS_ENABLED(CONFIG_RCU_EXP_KTHREAD))
|
||
sched_setscheduler_nocheck(kworker->task, SCHED_FIFO, ¶m);
|
||
}
|
||
|
||
static struct task_struct *rcu_exp_par_gp_task(struct rcu_node *rnp)
|
||
{
|
||
struct kthread_worker *kworker = READ_ONCE(rnp->exp_kworker);
|
||
|
||
if (!kworker)
|
||
return NULL;
|
||
|
||
return kworker->task;
|
||
}
|
||
|
||
static void __init rcu_start_exp_gp_kworker(void)
|
||
{
|
||
const char *name = "rcu_exp_gp_kthread_worker";
|
||
struct sched_param param = { .sched_priority = kthread_prio };
|
||
|
||
rcu_exp_gp_kworker = kthread_create_worker(0, name);
|
||
if (IS_ERR_OR_NULL(rcu_exp_gp_kworker)) {
|
||
pr_err("Failed to create %s!\n", name);
|
||
rcu_exp_gp_kworker = NULL;
|
||
return;
|
||
}
|
||
|
||
if (IS_ENABLED(CONFIG_RCU_EXP_KTHREAD))
|
||
sched_setscheduler_nocheck(rcu_exp_gp_kworker->task, SCHED_FIFO, ¶m);
|
||
}
|
||
|
||
static void rcu_spawn_rnp_kthreads(struct rcu_node *rnp)
|
||
{
|
||
if (rcu_scheduler_fully_active) {
|
||
mutex_lock(&rnp->kthread_mutex);
|
||
rcu_spawn_one_boost_kthread(rnp);
|
||
rcu_spawn_exp_par_gp_kworker(rnp);
|
||
mutex_unlock(&rnp->kthread_mutex);
|
||
}
|
||
}
|
||
|
||
/*
|
||
* Invoked early in the CPU-online process, when pretty much all services
|
||
* are available. The incoming CPU is not present.
|
||
*
|
||
* Initializes a CPU's per-CPU RCU data. Note that only one online or
|
||
* offline event can be happening at a given time. Note also that we can
|
||
* accept some slop in the rsp->gp_seq access due to the fact that this
|
||
* CPU cannot possibly have any non-offloaded RCU callbacks in flight yet.
|
||
* And any offloaded callbacks are being numbered elsewhere.
|
||
*/
|
||
int rcutree_prepare_cpu(unsigned int cpu)
|
||
{
|
||
unsigned long flags;
|
||
struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
|
||
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
|
||
struct rcu_node *rnp = rcu_get_root();
|
||
|
||
/* Set up local state, ensuring consistent view of global state. */
|
||
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
||
rdp->qlen_last_fqs_check = 0;
|
||
rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
|
||
rdp->blimit = blimit;
|
||
ct->nesting = 1; /* CPU not up, no tearing. */
|
||
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
|
||
|
||
/*
|
||
* Only non-NOCB CPUs that didn't have early-boot callbacks need to be
|
||
* (re-)initialized.
|
||
*/
|
||
if (!rcu_segcblist_is_enabled(&rdp->cblist))
|
||
rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */
|
||
|
||
/*
|
||
* Add CPU to leaf rcu_node pending-online bitmask. Any needed
|
||
* propagation up the rcu_node tree will happen at the beginning
|
||
* of the next grace period.
|
||
*/
|
||
rnp = rdp->mynode;
|
||
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
|
||
rdp->gp_seq = READ_ONCE(rnp->gp_seq);
|
||
rdp->gp_seq_needed = rdp->gp_seq;
|
||
rdp->cpu_no_qs.b.norm = true;
|
||
rdp->core_needs_qs = false;
|
||
rdp->rcu_iw_pending = false;
|
||
rdp->rcu_iw = IRQ_WORK_INIT_HARD(rcu_iw_handler);
|
||
rdp->rcu_iw_gp_seq = rdp->gp_seq - 1;
|
||
trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuonl"));
|
||
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
||
rcu_spawn_rnp_kthreads(rnp);
|
||
rcu_spawn_cpu_nocb_kthread(cpu);
|
||
ASSERT_EXCLUSIVE_WRITER(rcu_state.n_online_cpus);
|
||
WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus + 1);
|
||
|
||
return 0;
|
||
}
|
||
|
||
/*
|
||
* Update kthreads affinity during CPU-hotplug changes.
|
||
*
|
||
* Set the per-rcu_node kthread's affinity to cover all CPUs that are
|
||
* served by the rcu_node in question. The CPU hotplug lock is still
|
||
* held, so the value of rnp->qsmaskinit will be stable.
|
||
*
|
||
* We don't include outgoingcpu in the affinity set, use -1 if there is
|
||
* no outgoing CPU. If there are no CPUs left in the affinity set,
|
||
* this function allows the kthread to execute on any CPU.
|
||
*
|
||
* Any future concurrent calls are serialized via ->kthread_mutex.
|
||
*/
|
||
static void rcutree_affinity_setting(unsigned int cpu, int outgoingcpu)
|
||
{
|
||
cpumask_var_t cm;
|
||
unsigned long mask;
|
||
struct rcu_data *rdp;
|
||
struct rcu_node *rnp;
|
||
struct task_struct *task_boost, *task_exp;
|
||
|
||
rdp = per_cpu_ptr(&rcu_data, cpu);
|
||
rnp = rdp->mynode;
|
||
|
||
task_boost = rcu_boost_task(rnp);
|
||
task_exp = rcu_exp_par_gp_task(rnp);
|
||
|
||
/*
|
||
* If CPU is the boot one, those tasks are created later from early
|
||
* initcall since kthreadd must be created first.
|
||
*/
|
||
if (!task_boost && !task_exp)
|
||
return;
|
||
|
||
if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
|
||
return;
|
||
|
||
mutex_lock(&rnp->kthread_mutex);
|
||
mask = rcu_rnp_online_cpus(rnp);
|
||
for_each_leaf_node_possible_cpu(rnp, cpu)
|
||
if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
|
||
cpu != outgoingcpu)
|
||
cpumask_set_cpu(cpu, cm);
|
||
cpumask_and(cm, cm, housekeeping_cpumask(HK_TYPE_RCU));
|
||
if (cpumask_empty(cm)) {
|
||
cpumask_copy(cm, housekeeping_cpumask(HK_TYPE_RCU));
|
||
if (outgoingcpu >= 0)
|
||
cpumask_clear_cpu(outgoingcpu, cm);
|
||
}
|
||
|
||
if (task_exp)
|
||
set_cpus_allowed_ptr(task_exp, cm);
|
||
|
||
if (task_boost)
|
||
set_cpus_allowed_ptr(task_boost, cm);
|
||
|
||
mutex_unlock(&rnp->kthread_mutex);
|
||
|
||
free_cpumask_var(cm);
|
||
}
|
||
|
||
/*
|
||
* Has the specified (known valid) CPU ever been fully online?
|
||
*/
|
||
bool rcu_cpu_beenfullyonline(int cpu)
|
||
{
|
||
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
|
||
|
||
return smp_load_acquire(&rdp->beenonline);
|
||
}
|
||
|
||
/*
|
||
* Near the end of the CPU-online process. Pretty much all services
|
||
* enabled, and the CPU is now very much alive.
|
||
*/
|
||
int rcutree_online_cpu(unsigned int cpu)
|
||
{
|
||
unsigned long flags;
|
||
struct rcu_data *rdp;
|
||
struct rcu_node *rnp;
|
||
|
||
rdp = per_cpu_ptr(&rcu_data, cpu);
|
||
rnp = rdp->mynode;
|
||
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
||
rnp->ffmask |= rdp->grpmask;
|
||
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
||
if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
|
||
return 0; /* Too early in boot for scheduler work. */
|
||
sync_sched_exp_online_cleanup(cpu);
|
||
rcutree_affinity_setting(cpu, -1);
|
||
|
||
// Stop-machine done, so allow nohz_full to disable tick.
|
||
tick_dep_clear(TICK_DEP_BIT_RCU);
|
||
return 0;
|
||
}
|
||
|
||
/*
|
||
* Mark the specified CPU as being online so that subsequent grace periods
|
||
* (both expedited and normal) will wait on it. Note that this means that
|
||
* incoming CPUs are not allowed to use RCU read-side critical sections
|
||
* until this function is called. Failing to observe this restriction
|
||
* will result in lockdep splats.
|
||
*
|
||
* Note that this function is special in that it is invoked directly
|
||
* from the incoming CPU rather than from the cpuhp_step mechanism.
|
||
* This is because this function must be invoked at a precise location.
|
||
* This incoming CPU must not have enabled interrupts yet.
|
||
*
|
||
* This mirrors the effects of rcutree_report_cpu_dead().
|
||
*/
|
||
void rcutree_report_cpu_starting(unsigned int cpu)
|
||
{
|
||
unsigned long mask;
|
||
struct rcu_data *rdp;
|
||
struct rcu_node *rnp;
|
||
bool newcpu;
|
||
|
||
lockdep_assert_irqs_disabled();
|
||
rdp = per_cpu_ptr(&rcu_data, cpu);
|
||
if (rdp->cpu_started)
|
||
return;
|
||
rdp->cpu_started = true;
|
||
|
||
rnp = rdp->mynode;
|
||
mask = rdp->grpmask;
|
||
arch_spin_lock(&rcu_state.ofl_lock);
|
||
rcu_watching_online();
|
||
raw_spin_lock(&rcu_state.barrier_lock);
|
||
raw_spin_lock_rcu_node(rnp);
|
||
WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext | mask);
|
||
raw_spin_unlock(&rcu_state.barrier_lock);
|
||
newcpu = !(rnp->expmaskinitnext & mask);
|
||
rnp->expmaskinitnext |= mask;
|
||
/* Allow lockless access for expedited grace periods. */
|
||
smp_store_release(&rcu_state.ncpus, rcu_state.ncpus + newcpu); /* ^^^ */
|
||
ASSERT_EXCLUSIVE_WRITER(rcu_state.ncpus);
|
||
rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */
|
||
rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq);
|
||
rdp->rcu_onl_gp_state = READ_ONCE(rcu_state.gp_state);
|
||
|
||
/* An incoming CPU should never be blocking a grace period. */
|
||
if (WARN_ON_ONCE(rnp->qsmask & mask)) { /* RCU waiting on incoming CPU? */
|
||
/* rcu_report_qs_rnp() *really* wants some flags to restore */
|
||
unsigned long flags;
|
||
|
||
local_irq_save(flags);
|
||
rcu_disable_urgency_upon_qs(rdp);
|
||
/* Report QS -after- changing ->qsmaskinitnext! */
|
||
rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
|
||
} else {
|
||
raw_spin_unlock_rcu_node(rnp);
|
||
}
|
||
arch_spin_unlock(&rcu_state.ofl_lock);
|
||
smp_store_release(&rdp->beenonline, true);
|
||
smp_mb(); /* Ensure RCU read-side usage follows above initialization. */
|
||
}
|
||
|
||
/*
|
||
* The outgoing function has no further need of RCU, so remove it from
|
||
* the rcu_node tree's ->qsmaskinitnext bit masks.
|
||
*
|
||
* Note that this function is special in that it is invoked directly
|
||
* from the outgoing CPU rather than from the cpuhp_step mechanism.
|
||
* This is because this function must be invoked at a precise location.
|
||
*
|
||
* This mirrors the effect of rcutree_report_cpu_starting().
|
||
*/
|
||
void rcutree_report_cpu_dead(void)
|
||
{
|
||
unsigned long flags;
|
||
unsigned long mask;
|
||
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
|
||
struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
|
||
|
||
/*
|
||
* IRQS must be disabled from now on and until the CPU dies, or an interrupt
|
||
* may introduce a new READ-side while it is actually off the QS masks.
|
||
*/
|
||
lockdep_assert_irqs_disabled();
|
||
// Do any dangling deferred wakeups.
|
||
do_nocb_deferred_wakeup(rdp);
|
||
|
||
rcu_preempt_deferred_qs(current);
|
||
|
||
/* Remove outgoing CPU from mask in the leaf rcu_node structure. */
|
||
mask = rdp->grpmask;
|
||
arch_spin_lock(&rcu_state.ofl_lock);
|
||
raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
|
||
rdp->rcu_ofl_gp_seq = READ_ONCE(rcu_state.gp_seq);
|
||
rdp->rcu_ofl_gp_state = READ_ONCE(rcu_state.gp_state);
|
||
if (rnp->qsmask & mask) { /* RCU waiting on outgoing CPU? */
|
||
/* Report quiescent state -before- changing ->qsmaskinitnext! */
|
||
rcu_disable_urgency_upon_qs(rdp);
|
||
rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
|
||
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
||
}
|
||
WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext & ~mask);
|
||
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
||
arch_spin_unlock(&rcu_state.ofl_lock);
|
||
rdp->cpu_started = false;
|
||
}
|
||
|
||
#ifdef CONFIG_HOTPLUG_CPU
|
||
/*
|
||
* The outgoing CPU has just passed through the dying-idle state, and we
|
||
* are being invoked from the CPU that was IPIed to continue the offline
|
||
* operation. Migrate the outgoing CPU's callbacks to the current CPU.
|
||
*/
|
||
void rcutree_migrate_callbacks(int cpu)
|
||
{
|
||
unsigned long flags;
|
||
struct rcu_data *my_rdp;
|
||
struct rcu_node *my_rnp;
|
||
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
|
||
bool needwake;
|
||
|
||
if (rcu_rdp_is_offloaded(rdp))
|
||
return;
|
||
|
||
raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags);
|
||
if (rcu_segcblist_empty(&rdp->cblist)) {
|
||
raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
|
||
return; /* No callbacks to migrate. */
|
||
}
|
||
|
||
WARN_ON_ONCE(rcu_rdp_cpu_online(rdp));
|
||
rcu_barrier_entrain(rdp);
|
||
my_rdp = this_cpu_ptr(&rcu_data);
|
||
my_rnp = my_rdp->mynode;
|
||
rcu_nocb_lock(my_rdp); /* irqs already disabled. */
|
||
WARN_ON_ONCE(!rcu_nocb_flush_bypass(my_rdp, NULL, jiffies, false));
|
||
raw_spin_lock_rcu_node(my_rnp); /* irqs already disabled. */
|
||
/* Leverage recent GPs and set GP for new callbacks. */
|
||
needwake = rcu_advance_cbs(my_rnp, rdp) ||
|
||
rcu_advance_cbs(my_rnp, my_rdp);
|
||
rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist);
|
||
raw_spin_unlock(&rcu_state.barrier_lock); /* irqs remain disabled. */
|
||
needwake = needwake || rcu_advance_cbs(my_rnp, my_rdp);
|
||
rcu_segcblist_disable(&rdp->cblist);
|
||
WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) != !rcu_segcblist_n_cbs(&my_rdp->cblist));
|
||
check_cb_ovld_locked(my_rdp, my_rnp);
|
||
if (rcu_rdp_is_offloaded(my_rdp)) {
|
||
raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */
|
||
__call_rcu_nocb_wake(my_rdp, true, flags);
|
||
} else {
|
||
rcu_nocb_unlock(my_rdp); /* irqs remain disabled. */
|
||
raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */
|
||
}
|
||
local_irq_restore(flags);
|
||
if (needwake)
|
||
rcu_gp_kthread_wake();
|
||
lockdep_assert_irqs_enabled();
|
||
WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||
|
||
!rcu_segcblist_empty(&rdp->cblist),
|
||
"rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n",
|
||
cpu, rcu_segcblist_n_cbs(&rdp->cblist),
|
||
rcu_segcblist_first_cb(&rdp->cblist));
|
||
}
|
||
|
||
/*
|
||
* The CPU has been completely removed, and some other CPU is reporting
|
||
* this fact from process context. Do the remainder of the cleanup.
|
||
* There can only be one CPU hotplug operation at a time, so no need for
|
||
* explicit locking.
|
||
*/
|
||
int rcutree_dead_cpu(unsigned int cpu)
|
||
{
|
||
ASSERT_EXCLUSIVE_WRITER(rcu_state.n_online_cpus);
|
||
WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1);
|
||
// Stop-machine done, so allow nohz_full to disable tick.
|
||
tick_dep_clear(TICK_DEP_BIT_RCU);
|
||
return 0;
|
||
}
|
||
|
||
/*
|
||
* Near the end of the offline process. Trace the fact that this CPU
|
||
* is going offline.
|
||
*/
|
||
int rcutree_dying_cpu(unsigned int cpu)
|
||
{
|
||
bool blkd;
|
||
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
|
||
struct rcu_node *rnp = rdp->mynode;
|
||
|
||
blkd = !!(READ_ONCE(rnp->qsmask) & rdp->grpmask);
|
||
trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
|
||
blkd ? TPS("cpuofl-bgp") : TPS("cpuofl"));
|
||
return 0;
|
||
}
|
||
|
||
/*
|
||
* Near the beginning of the process. The CPU is still very much alive
|
||
* with pretty much all services enabled.
|
||
*/
|
||
int rcutree_offline_cpu(unsigned int cpu)
|
||
{
|
||
unsigned long flags;
|
||
struct rcu_data *rdp;
|
||
struct rcu_node *rnp;
|
||
|
||
rdp = per_cpu_ptr(&rcu_data, cpu);
|
||
rnp = rdp->mynode;
|
||
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
||
rnp->ffmask &= ~rdp->grpmask;
|
||
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
||
|
||
rcutree_affinity_setting(cpu, cpu);
|
||
|
||
// nohz_full CPUs need the tick for stop-machine to work quickly
|
||
tick_dep_set(TICK_DEP_BIT_RCU);
|
||
return 0;
|
||
}
|
||
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
|
||
|
||
/*
|
||
* On non-huge systems, use expedited RCU grace periods to make suspend
|
||
* and hibernation run faster.
|
||
*/
|
||
static int rcu_pm_notify(struct notifier_block *self,
|
||
unsigned long action, void *hcpu)
|
||
{
|
||
switch (action) {
|
||
case PM_HIBERNATION_PREPARE:
|
||
case PM_SUSPEND_PREPARE:
|
||
rcu_async_hurry();
|
||
rcu_expedite_gp();
|
||
break;
|
||
case PM_POST_HIBERNATION:
|
||
case PM_POST_SUSPEND:
|
||
rcu_unexpedite_gp();
|
||
rcu_async_relax();
|
||
break;
|
||
default:
|
||
break;
|
||
}
|
||
return NOTIFY_OK;
|
||
}
|
||
|
||
/*
|
||
* Spawn the kthreads that handle RCU's grace periods.
|
||
*/
|
||
static int __init rcu_spawn_gp_kthread(void)
|
||
{
|
||
unsigned long flags;
|
||
struct rcu_node *rnp;
|
||
struct sched_param sp;
|
||
struct task_struct *t;
|
||
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
|
||
|
||
rcu_scheduler_fully_active = 1;
|
||
t = kthread_create(rcu_gp_kthread, NULL, "%s", rcu_state.name);
|
||
if (WARN_ONCE(IS_ERR(t), "%s: Could not start grace-period kthread, OOM is now expected behavior\n", __func__))
|
||
return 0;
|
||
if (kthread_prio) {
|
||
sp.sched_priority = kthread_prio;
|
||
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
|
||
}
|
||
rnp = rcu_get_root();
|
||
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
||
WRITE_ONCE(rcu_state.gp_activity, jiffies);
|
||
WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
|
||
// Reset .gp_activity and .gp_req_activity before setting .gp_kthread.
|
||
smp_store_release(&rcu_state.gp_kthread, t); /* ^^^ */
|
||
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
||
wake_up_process(t);
|
||
/* This is a pre-SMP initcall, we expect a single CPU */
|
||
WARN_ON(num_online_cpus() > 1);
|
||
/*
|
||
* Those kthreads couldn't be created on rcu_init() -> rcutree_prepare_cpu()
|
||
* due to rcu_scheduler_fully_active.
|
||
*/
|
||
rcu_spawn_cpu_nocb_kthread(smp_processor_id());
|
||
rcu_spawn_rnp_kthreads(rdp->mynode);
|
||
rcu_spawn_core_kthreads();
|
||
/* Create kthread worker for expedited GPs */
|
||
rcu_start_exp_gp_kworker();
|
||
return 0;
|
||
}
|
||
early_initcall(rcu_spawn_gp_kthread);
|
||
|
||
/*
|
||
* This function is invoked towards the end of the scheduler's
|
||
* initialization process. Before this is called, the idle task might
|
||
* contain synchronous grace-period primitives (during which time, this idle
|
||
* task is booting the system, and such primitives are no-ops). After this
|
||
* function is called, any synchronous grace-period primitives are run as
|
||
* expedited, with the requesting task driving the grace period forward.
|
||
* A later core_initcall() rcu_set_runtime_mode() will switch to full
|
||
* runtime RCU functionality.
|
||
*/
|
||
void rcu_scheduler_starting(void)
|
||
{
|
||
unsigned long flags;
|
||
struct rcu_node *rnp;
|
||
|
||
WARN_ON(num_online_cpus() != 1);
|
||
WARN_ON(nr_context_switches() > 0);
|
||
rcu_test_sync_prims();
|
||
|
||
// Fix up the ->gp_seq counters.
|
||
local_irq_save(flags);
|
||
rcu_for_each_node_breadth_first(rnp)
|
||
rnp->gp_seq_needed = rnp->gp_seq = rcu_state.gp_seq;
|
||
local_irq_restore(flags);
|
||
|
||
// Switch out of early boot mode.
|
||
rcu_scheduler_active = RCU_SCHEDULER_INIT;
|
||
rcu_test_sync_prims();
|
||
}
|
||
|
||
/*
|
||
* Helper function for rcu_init() that initializes the rcu_state structure.
|
||
*/
|
||
static void __init rcu_init_one(void)
|
||
{
|
||
static const char * const buf[] = RCU_NODE_NAME_INIT;
|
||
static const char * const fqs[] = RCU_FQS_NAME_INIT;
|
||
static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
|
||
static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
|
||
|
||
int levelspread[RCU_NUM_LVLS]; /* kids/node in each level. */
|
||
int cpustride = 1;
|
||
int i;
|
||
int j;
|
||
struct rcu_node *rnp;
|
||
|
||
BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
|
||
|
||
/* Silence gcc 4.8 false positive about array index out of range. */
|
||
if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
|
||
panic("rcu_init_one: rcu_num_lvls out of range");
|
||
|
||
/* Initialize the level-tracking arrays. */
|
||
|
||
for (i = 1; i < rcu_num_lvls; i++)
|
||
rcu_state.level[i] =
|
||
rcu_state.level[i - 1] + num_rcu_lvl[i - 1];
|
||
rcu_init_levelspread(levelspread, num_rcu_lvl);
|
||
|
||
/* Initialize the elements themselves, starting from the leaves. */
|
||
|
||
for (i = rcu_num_lvls - 1; i >= 0; i--) {
|
||
cpustride *= levelspread[i];
|
||
rnp = rcu_state.level[i];
|
||
for (j = 0; j < num_rcu_lvl[i]; j++, rnp++) {
|
||
raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock));
|
||
lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock),
|
||
&rcu_node_class[i], buf[i]);
|
||
raw_spin_lock_init(&rnp->fqslock);
|
||
lockdep_set_class_and_name(&rnp->fqslock,
|
||
&rcu_fqs_class[i], fqs[i]);
|
||
rnp->gp_seq = rcu_state.gp_seq;
|
||
rnp->gp_seq_needed = rcu_state.gp_seq;
|
||
rnp->completedqs = rcu_state.gp_seq;
|
||
rnp->qsmask = 0;
|
||
rnp->qsmaskinit = 0;
|
||
rnp->grplo = j * cpustride;
|
||
rnp->grphi = (j + 1) * cpustride - 1;
|
||
if (rnp->grphi >= nr_cpu_ids)
|
||
rnp->grphi = nr_cpu_ids - 1;
|
||
if (i == 0) {
|
||
rnp->grpnum = 0;
|
||
rnp->grpmask = 0;
|
||
rnp->parent = NULL;
|
||
} else {
|
||
rnp->grpnum = j % levelspread[i - 1];
|
||
rnp->grpmask = BIT(rnp->grpnum);
|
||
rnp->parent = rcu_state.level[i - 1] +
|
||
j / levelspread[i - 1];
|
||
}
|
||
rnp->level = i;
|
||
INIT_LIST_HEAD(&rnp->blkd_tasks);
|
||
rcu_init_one_nocb(rnp);
|
||
init_waitqueue_head(&rnp->exp_wq[0]);
|
||
init_waitqueue_head(&rnp->exp_wq[1]);
|
||
init_waitqueue_head(&rnp->exp_wq[2]);
|
||
init_waitqueue_head(&rnp->exp_wq[3]);
|
||
spin_lock_init(&rnp->exp_lock);
|
||
mutex_init(&rnp->kthread_mutex);
|
||
raw_spin_lock_init(&rnp->exp_poll_lock);
|
||
rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
|
||
INIT_WORK(&rnp->exp_poll_wq, sync_rcu_do_polled_gp);
|
||
}
|
||
}
|
||
|
||
init_swait_queue_head(&rcu_state.gp_wq);
|
||
init_swait_queue_head(&rcu_state.expedited_wq);
|
||
rnp = rcu_first_leaf_node();
|
||
for_each_possible_cpu(i) {
|
||
while (i > rnp->grphi)
|
||
rnp++;
|
||
per_cpu_ptr(&rcu_data, i)->mynode = rnp;
|
||
per_cpu_ptr(&rcu_data, i)->barrier_head.next =
|
||
&per_cpu_ptr(&rcu_data, i)->barrier_head;
|
||
rcu_boot_init_percpu_data(i);
|
||
}
|
||
}
|
||
|
||
/*
|
||
* Force priority from the kernel command-line into range.
|
||
*/
|
||
static void __init sanitize_kthread_prio(void)
|
||
{
|
||
int kthread_prio_in = kthread_prio;
|
||
|
||
if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 2
|
||
&& IS_BUILTIN(CONFIG_RCU_TORTURE_TEST))
|
||
kthread_prio = 2;
|
||
else if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
|
||
kthread_prio = 1;
|
||
else if (kthread_prio < 0)
|
||
kthread_prio = 0;
|
||
else if (kthread_prio > 99)
|
||
kthread_prio = 99;
|
||
|
||
if (kthread_prio != kthread_prio_in)
|
||
pr_alert("%s: Limited prio to %d from %d\n",
|
||
__func__, kthread_prio, kthread_prio_in);
|
||
}
|
||
|
||
/*
|
||
* Compute the rcu_node tree geometry from kernel parameters. This cannot
|
||
* replace the definitions in tree.h because those are needed to size
|
||
* the ->node array in the rcu_state structure.
|
||
*/
|
||
void rcu_init_geometry(void)
|
||
{
|
||
ulong d;
|
||
int i;
|
||
static unsigned long old_nr_cpu_ids;
|
||
int rcu_capacity[RCU_NUM_LVLS];
|
||
static bool initialized;
|
||
|
||
if (initialized) {
|
||
/*
|
||
* Warn if setup_nr_cpu_ids() had not yet been invoked,
|
||
* unless nr_cpus_ids == NR_CPUS, in which case who cares?
|
||
*/
|
||
WARN_ON_ONCE(old_nr_cpu_ids != nr_cpu_ids);
|
||
return;
|
||
}
|
||
|
||
old_nr_cpu_ids = nr_cpu_ids;
|
||
initialized = true;
|
||
|
||
/*
|
||
* Initialize any unspecified boot parameters.
|
||
* The default values of jiffies_till_first_fqs and
|
||
* jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
|
||
* value, which is a function of HZ, then adding one for each
|
||
* RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
|
||
*/
|
||
d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
|
||
if (jiffies_till_first_fqs == ULONG_MAX)
|
||
jiffies_till_first_fqs = d;
|
||
if (jiffies_till_next_fqs == ULONG_MAX)
|
||
jiffies_till_next_fqs = d;
|
||
adjust_jiffies_till_sched_qs();
|
||
|
||
/* If the compile-time values are accurate, just leave. */
|
||
if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
|
||
nr_cpu_ids == NR_CPUS)
|
||
return;
|
||
pr_info("Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%u\n",
|
||
rcu_fanout_leaf, nr_cpu_ids);
|
||
|
||
/*
|
||
* The boot-time rcu_fanout_leaf parameter must be at least two
|
||
* and cannot exceed the number of bits in the rcu_node masks.
|
||
* Complain and fall back to the compile-time values if this
|
||
* limit is exceeded.
|
||
*/
|
||
if (rcu_fanout_leaf < 2 ||
|
||
rcu_fanout_leaf > sizeof(unsigned long) * 8) {
|
||
rcu_fanout_leaf = RCU_FANOUT_LEAF;
|
||
WARN_ON(1);
|
||
return;
|
||
}
|
||
|
||
/*
|
||
* Compute number of nodes that can be handled an rcu_node tree
|
||
* with the given number of levels.
|
||
*/
|
||
rcu_capacity[0] = rcu_fanout_leaf;
|
||
for (i = 1; i < RCU_NUM_LVLS; i++)
|
||
rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
|
||
|
||
/*
|
||
* The tree must be able to accommodate the configured number of CPUs.
|
||
* If this limit is exceeded, fall back to the compile-time values.
|
||
*/
|
||
if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) {
|
||
rcu_fanout_leaf = RCU_FANOUT_LEAF;
|
||
WARN_ON(1);
|
||
return;
|
||
}
|
||
|
||
/* Calculate the number of levels in the tree. */
|
||
for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
|
||
}
|
||
rcu_num_lvls = i + 1;
|
||
|
||
/* Calculate the number of rcu_nodes at each level of the tree. */
|
||
for (i = 0; i < rcu_num_lvls; i++) {
|
||
int cap = rcu_capacity[(rcu_num_lvls - 1) - i];
|
||
num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
|
||
}
|
||
|
||
/* Calculate the total number of rcu_node structures. */
|
||
rcu_num_nodes = 0;
|
||
for (i = 0; i < rcu_num_lvls; i++)
|
||
rcu_num_nodes += num_rcu_lvl[i];
|
||
}
|
||
|
||
/*
|
||
* Dump out the structure of the rcu_node combining tree associated
|
||
* with the rcu_state structure.
|
||
*/
|
||
static void __init rcu_dump_rcu_node_tree(void)
|
||
{
|
||
int level = 0;
|
||
struct rcu_node *rnp;
|
||
|
||
pr_info("rcu_node tree layout dump\n");
|
||
pr_info(" ");
|
||
rcu_for_each_node_breadth_first(rnp) {
|
||
if (rnp->level != level) {
|
||
pr_cont("\n");
|
||
pr_info(" ");
|
||
level = rnp->level;
|
||
}
|
||
pr_cont("%d:%d ^%d ", rnp->grplo, rnp->grphi, rnp->grpnum);
|
||
}
|
||
pr_cont("\n");
|
||
}
|
||
|
||
struct workqueue_struct *rcu_gp_wq;
|
||
|
||
static void __init kfree_rcu_batch_init(void)
|
||
{
|
||
int cpu;
|
||
int i, j;
|
||
struct shrinker *kfree_rcu_shrinker;
|
||
|
||
/* Clamp it to [0:100] seconds interval. */
|
||
if (rcu_delay_page_cache_fill_msec < 0 ||
|
||
rcu_delay_page_cache_fill_msec > 100 * MSEC_PER_SEC) {
|
||
|
||
rcu_delay_page_cache_fill_msec =
|
||
clamp(rcu_delay_page_cache_fill_msec, 0,
|
||
(int) (100 * MSEC_PER_SEC));
|
||
|
||
pr_info("Adjusting rcutree.rcu_delay_page_cache_fill_msec to %d ms.\n",
|
||
rcu_delay_page_cache_fill_msec);
|
||
}
|
||
|
||
for_each_possible_cpu(cpu) {
|
||
struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
|
||
|
||
for (i = 0; i < KFREE_N_BATCHES; i++) {
|
||
INIT_RCU_WORK(&krcp->krw_arr[i].rcu_work, kfree_rcu_work);
|
||
krcp->krw_arr[i].krcp = krcp;
|
||
|
||
for (j = 0; j < FREE_N_CHANNELS; j++)
|
||
INIT_LIST_HEAD(&krcp->krw_arr[i].bulk_head_free[j]);
|
||
}
|
||
|
||
for (i = 0; i < FREE_N_CHANNELS; i++)
|
||
INIT_LIST_HEAD(&krcp->bulk_head[i]);
|
||
|
||
INIT_DELAYED_WORK(&krcp->monitor_work, kfree_rcu_monitor);
|
||
INIT_DELAYED_WORK(&krcp->page_cache_work, fill_page_cache_func);
|
||
krcp->initialized = true;
|
||
}
|
||
|
||
kfree_rcu_shrinker = shrinker_alloc(0, "rcu-kfree");
|
||
if (!kfree_rcu_shrinker) {
|
||
pr_err("Failed to allocate kfree_rcu() shrinker!\n");
|
||
return;
|
||
}
|
||
|
||
kfree_rcu_shrinker->count_objects = kfree_rcu_shrink_count;
|
||
kfree_rcu_shrinker->scan_objects = kfree_rcu_shrink_scan;
|
||
|
||
shrinker_register(kfree_rcu_shrinker);
|
||
}
|
||
|
||
void __init rcu_init(void)
|
||
{
|
||
int cpu = smp_processor_id();
|
||
|
||
rcu_early_boot_tests();
|
||
|
||
kfree_rcu_batch_init();
|
||
rcu_bootup_announce();
|
||
sanitize_kthread_prio();
|
||
rcu_init_geometry();
|
||
rcu_init_one();
|
||
if (dump_tree)
|
||
rcu_dump_rcu_node_tree();
|
||
if (use_softirq)
|
||
open_softirq(RCU_SOFTIRQ, rcu_core_si);
|
||
|
||
/*
|
||
* We don't need protection against CPU-hotplug here because
|
||
* this is called early in boot, before either interrupts
|
||
* or the scheduler are operational.
|
||
*/
|
||
pm_notifier(rcu_pm_notify, 0);
|
||
WARN_ON(num_online_cpus() > 1); // Only one CPU this early in boot.
|
||
rcutree_prepare_cpu(cpu);
|
||
rcutree_report_cpu_starting(cpu);
|
||
rcutree_online_cpu(cpu);
|
||
|
||
/* Create workqueue for Tree SRCU and for expedited GPs. */
|
||
rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
|
||
WARN_ON(!rcu_gp_wq);
|
||
|
||
sync_wq = alloc_workqueue("sync_wq", WQ_MEM_RECLAIM, 0);
|
||
WARN_ON(!sync_wq);
|
||
|
||
/* Fill in default value for rcutree.qovld boot parameter. */
|
||
/* -After- the rcu_node ->lock fields are initialized! */
|
||
if (qovld < 0)
|
||
qovld_calc = DEFAULT_RCU_QOVLD_MULT * qhimark;
|
||
else
|
||
qovld_calc = qovld;
|
||
|
||
// Kick-start in case any polled grace periods started early.
|
||
(void)start_poll_synchronize_rcu_expedited();
|
||
|
||
rcu_test_sync_prims();
|
||
|
||
tasks_cblist_init_generic();
|
||
}
|
||
|
||
#include "tree_stall.h"
|
||
#include "tree_exp.h"
|
||
#include "tree_nocb.h"
|
||
#include "tree_plugin.h"
|