/* * 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 <dipankar@in.ibm.com> * Manfred Spraul <manfred@colorfullife.com> * * Based on the original work by Paul McKenney <paulmck@us.ibm.com> * 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 <linux/types.h> #include <linux/kernel.h> #include <linux/init.h> #include <linux/spinlock.h> #include <linux/smp.h> #include <linux/interrupt.h> #include <linux/sched.h> #include <asm/atomic.h> #include <linux/bitops.h> #include <linux/completion.h> #include <linux/percpu.h> #include <linux/notifier.h> #include <linux/cpu.h> #include <linux/mutex.h> #include <linux/module.h> struct rcu_synchronize { struct rcu_head head; struct completion completion; }; 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; /* * Awaken the corresponding synchronize_rcu() instance now that a * grace period has elapsed. */ static 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; 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 *notused) { int cpu = smp_processor_id(); struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu); atomic_inc(&rcu_barrier_cpu_count); call_rcu(head, rcu_barrier_callback); } /** * rcu_barrier - Wait until all the in-flight RCUs are complete. */ void rcu_barrier(void) { BUG_ON(in_interrupt()); /* Take cpucontrol mutex to protect against CPU hotplug */ mutex_lock(&rcu_barrier_mutex); init_completion(&rcu_barrier_completion); atomic_set(&rcu_barrier_cpu_count, 0); /* * The queueing of callbacks in all CPUs must be atomic with * respect to RCU, otherwise one CPU may queue a callback, * wait for a grace period, decrement barrier count and call * complete(), while other CPUs have not yet queued anything. * So, we need to make sure that grace periods cannot complete * until all the callbacks are queued. */ rcu_read_lock(); on_each_cpu(rcu_barrier_func, NULL, 0, 1); rcu_read_unlock(); wait_for_completion(&rcu_barrier_completion); mutex_unlock(&rcu_barrier_mutex); } EXPORT_SYMBOL_GPL(rcu_barrier); void __init rcu_init(void) { __rcu_init(); }