/* * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition. * * 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, you can access it online at * http://www.gnu.org/licenses/gpl-2.0.html. * * Copyright IBM Corporation, 2008 * * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com> * * For detailed explanation of Read-Copy Update mechanism see - *		Documentation/RCU */#include <linux/completion.h>#include <linux/interrupt.h>#include <linux/notifier.h>#include <linux/rcupdate_wait.h>#include <linux/kernel.h>#include <linux/export.h>#include <linux/mutex.h>#include <linux/sched.h>#include <linux/types.h>#include <linux/init.h>#include <linux/time.h>#include <linux/cpu.h>#include <linux/prefetch.h> #include "rcu.h" /* Global control variables for rcupdate callback mechanism. */struct rcu_ctrlblk {	struct rcu_head *rcucblist;	/* List of pending callbacks (CBs). */	struct rcu_head **donetail;	/* ->next pointer of last "done" CB. */	struct rcu_head **curtail;	/* ->next pointer of last CB. */}; /* Definition for rcupdate control block. */static struct rcu_ctrlblk rcu_ctrlblk = {	.donetail	= &rcu_ctrlblk.rcucblist,	.curtail	= &rcu_ctrlblk.rcucblist,}; void rcu_barrier(void){	wait_rcu_gp(call_rcu);}EXPORT_SYMBOL(rcu_barrier); /* Record an rcu quiescent state.  */void rcu_qs(void){	unsigned long flags; 	local_irq_save(flags);	if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {		rcu_ctrlblk.donetail = rcu_ctrlblk.curtail;		raise_softirq(RCU_SOFTIRQ);	}	local_irq_restore(flags);} /* * Check to see if the scheduling-clock interrupt came from an extended * quiescent state, and, if so, tell RCU about it.  This function must * be called from hardirq context.  It is normally called from the * scheduling-clock interrupt. */void rcu_check_callbacks(int user){	if (user) {		rcu_qs();	} else if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {		set_tsk_need_resched(current);		set_preempt_need_resched();	}} /* Invoke the RCU callbacks whose grace period has elapsed.  */static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused){	struct rcu_head *next, *list;	unsigned long flags; 	/* Move the ready-to-invoke callbacks to a local list. */	local_irq_save(flags);	if (rcu_ctrlblk.donetail == &rcu_ctrlblk.rcucblist) {		/* No callbacks ready, so just leave. */		local_irq_restore(flags);		return;	}	list = rcu_ctrlblk.rcucblist;	rcu_ctrlblk.rcucblist = *rcu_ctrlblk.donetail;	*rcu_ctrlblk.donetail = NULL;	if (rcu_ctrlblk.curtail == rcu_ctrlblk.donetail)		rcu_ctrlblk.curtail = &rcu_ctrlblk.rcucblist;	rcu_ctrlblk.donetail = &rcu_ctrlblk.rcucblist;	local_irq_restore(flags); 	/* Invoke the callbacks on the local list. */	while (list) {		next = list->next;		prefetch(next);		debug_rcu_head_unqueue(list);		local_bh_disable();		__rcu_reclaim("", list);		local_bh_enable();		list = next;	}} /* * Wait for a grace period to elapse.  But it is illegal to invoke * synchronize_rcu() from within an RCU read-side critical section. * Therefore, any legal call to synchronize_rcu() is a quiescent * state, and so on a UP system, synchronize_rcu() need do nothing. * (But Lai Jiangshan points out the benefits of doing might_sleep() * to reduce latency.) * * Cool, huh?  (Due to Josh Triplett.) */void synchronize_rcu(void){	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");}EXPORT_SYMBOL_GPL(synchronize_rcu); /* * Post an RCU callback to be invoked after the end of an RCU grace * period.  But since we have but one CPU, that would be after any * quiescent state. */void call_rcu(struct rcu_head *head, rcu_callback_t func){	unsigned long flags; 	debug_rcu_head_queue(head);	head->func = func;	head->next = NULL; 	local_irq_save(flags);	*rcu_ctrlblk.curtail = head;	rcu_ctrlblk.curtail = &head->next;	local_irq_restore(flags); 	if (unlikely(is_idle_task(current))) {		/* force scheduling for rcu_qs() */		resched_cpu(0);	}}EXPORT_SYMBOL_GPL(call_rcu); void __init rcu_init(void){	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);	rcu_early_boot_tests();	srcu_init();}