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