/* * 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();}