232 lines
6.6 KiB
C
232 lines
6.6 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*
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* Copyright IBM Corporation, 2001
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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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*
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* Based on the original work by Paul McKenney <paulmck@us.ibm.com>
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* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
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* Papers:
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* http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
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* http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
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*
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* For detailed explanation of Read-Copy Update mechanism see -
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* http://lse.sourceforge.net/locking/rcupdate.html
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*
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*/
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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/interrupt.h>
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#include <linux/sched.h>
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#include <asm/atomic.h>
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#include <linux/bitops.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/module.h>
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#include <linux/kernel_stat.h>
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enum rcu_barrier {
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RCU_BARRIER_STD,
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RCU_BARRIER_BH,
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RCU_BARRIER_SCHED,
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};
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static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
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static atomic_t rcu_barrier_cpu_count;
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static DEFINE_MUTEX(rcu_barrier_mutex);
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static struct completion rcu_barrier_completion;
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int rcu_scheduler_active __read_mostly;
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static atomic_t rcu_migrate_type_count = ATOMIC_INIT(0);
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static struct rcu_head rcu_migrate_head[3];
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static DECLARE_WAIT_QUEUE_HEAD(rcu_migrate_wq);
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/*
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* Awaken the corresponding synchronize_rcu() instance now that a
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* grace period has elapsed.
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*/
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void wakeme_after_rcu(struct rcu_head *head)
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{
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struct rcu_synchronize *rcu;
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rcu = container_of(head, struct rcu_synchronize, head);
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complete(&rcu->completion);
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}
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/**
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* synchronize_rcu - wait until a grace period has elapsed.
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*
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* Control will return to the caller some time after a full grace
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* period has elapsed, in other words after all currently executing RCU
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* read-side critical sections have completed. RCU read-side critical
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* sections are delimited by rcu_read_lock() and rcu_read_unlock(),
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* and may be nested.
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*/
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void synchronize_rcu(void)
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{
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struct rcu_synchronize rcu;
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if (rcu_blocking_is_gp())
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return;
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init_completion(&rcu.completion);
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/* Will wake me after RCU finished. */
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call_rcu(&rcu.head, wakeme_after_rcu);
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/* Wait for it. */
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wait_for_completion(&rcu.completion);
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}
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EXPORT_SYMBOL_GPL(synchronize_rcu);
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static void rcu_barrier_callback(struct rcu_head *notused)
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{
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if (atomic_dec_and_test(&rcu_barrier_cpu_count))
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complete(&rcu_barrier_completion);
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}
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/*
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* Called with preemption disabled, and from cross-cpu IRQ context.
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*/
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static void rcu_barrier_func(void *type)
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{
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int cpu = smp_processor_id();
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struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
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atomic_inc(&rcu_barrier_cpu_count);
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switch ((enum rcu_barrier)type) {
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case RCU_BARRIER_STD:
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call_rcu(head, rcu_barrier_callback);
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break;
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case RCU_BARRIER_BH:
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call_rcu_bh(head, rcu_barrier_callback);
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break;
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case RCU_BARRIER_SCHED:
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call_rcu_sched(head, rcu_barrier_callback);
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break;
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}
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}
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static inline void wait_migrated_callbacks(void)
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{
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wait_event(rcu_migrate_wq, !atomic_read(&rcu_migrate_type_count));
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}
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/*
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* Orchestrate the specified type of RCU barrier, waiting for all
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* RCU callbacks of the specified type to complete.
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*/
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static void _rcu_barrier(enum rcu_barrier type)
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{
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BUG_ON(in_interrupt());
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/* Take cpucontrol mutex to protect against CPU hotplug */
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mutex_lock(&rcu_barrier_mutex);
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init_completion(&rcu_barrier_completion);
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/*
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* Initialize rcu_barrier_cpu_count to 1, then invoke
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* rcu_barrier_func() on each CPU, so that each CPU also has
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* incremented rcu_barrier_cpu_count. Only then is it safe to
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* decrement rcu_barrier_cpu_count -- otherwise the first CPU
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* might complete its grace period before all of the other CPUs
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* did their increment, causing this function to return too
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* early.
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*/
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atomic_set(&rcu_barrier_cpu_count, 1);
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on_each_cpu(rcu_barrier_func, (void *)type, 1);
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if (atomic_dec_and_test(&rcu_barrier_cpu_count))
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complete(&rcu_barrier_completion);
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wait_for_completion(&rcu_barrier_completion);
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mutex_unlock(&rcu_barrier_mutex);
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wait_migrated_callbacks();
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}
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/**
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* rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
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*/
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void rcu_barrier(void)
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{
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_rcu_barrier(RCU_BARRIER_STD);
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}
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EXPORT_SYMBOL_GPL(rcu_barrier);
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/**
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* rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
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*/
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void rcu_barrier_bh(void)
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{
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_rcu_barrier(RCU_BARRIER_BH);
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}
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EXPORT_SYMBOL_GPL(rcu_barrier_bh);
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/**
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* rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
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*/
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void rcu_barrier_sched(void)
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{
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_rcu_barrier(RCU_BARRIER_SCHED);
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}
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EXPORT_SYMBOL_GPL(rcu_barrier_sched);
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static void rcu_migrate_callback(struct rcu_head *notused)
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{
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if (atomic_dec_and_test(&rcu_migrate_type_count))
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wake_up(&rcu_migrate_wq);
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}
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static int __cpuinit rcu_barrier_cpu_hotplug(struct notifier_block *self,
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unsigned long action, void *hcpu)
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{
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if (action == CPU_DYING) {
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/*
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* preempt_disable() in on_each_cpu() prevents stop_machine(),
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* so when "on_each_cpu(rcu_barrier_func, (void *)type, 1);"
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* returns, all online cpus have queued rcu_barrier_func(),
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* and the dead cpu(if it exist) queues rcu_migrate_callback()s.
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*
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* These callbacks ensure _rcu_barrier() waits for all
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* RCU callbacks of the specified type to complete.
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*/
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atomic_set(&rcu_migrate_type_count, 3);
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call_rcu_bh(rcu_migrate_head, rcu_migrate_callback);
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call_rcu_sched(rcu_migrate_head + 1, rcu_migrate_callback);
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call_rcu(rcu_migrate_head + 2, rcu_migrate_callback);
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} else if (action == CPU_POST_DEAD) {
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/* rcu_migrate_head is protected by cpu_add_remove_lock */
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wait_migrated_callbacks();
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}
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return NOTIFY_OK;
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}
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void __init rcu_init(void)
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{
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__rcu_init();
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hotcpu_notifier(rcu_barrier_cpu_hotplug, 0);
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}
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void rcu_scheduler_starting(void)
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{
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WARN_ON(num_online_cpus() != 1);
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WARN_ON(nr_context_switches() > 0);
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rcu_scheduler_active = 1;
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}
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