/* * 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, write to the Free Software * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. * * 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.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> #ifdef CONFIG_RCU_TRACE#include <trace/events/rcu.h>#endif /* #else #ifdef CONFIG_RCU_TRACE */ #include "rcu.h" /* Forward declarations for rcutiny_plugin.h. */struct rcu_ctrlblk;static void invoke_rcu_callbacks(void);static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);static void rcu_process_callbacks(struct softirq_action *unused);static void __call_rcu(struct rcu_head *head,		       void (*func)(struct rcu_head *rcu),		       struct rcu_ctrlblk *rcp); #include "rcutiny_plugin.h" #ifdef CONFIG_NO_HZ static long rcu_dynticks_nesting = 1; /* * Enter dynticks-idle mode, which is an extended quiescent state * if we have fully entered that mode (i.e., if the new value of * dynticks_nesting is zero). */void rcu_enter_nohz(void){	if (--rcu_dynticks_nesting == 0)		rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */} /* * Exit dynticks-idle mode, so that we are no longer in an extended * quiescent state. */void rcu_exit_nohz(void){	rcu_dynticks_nesting++;} #endif /* #ifdef CONFIG_NO_HZ */ /* * Helper function for rcu_sched_qs() and rcu_bh_qs(). * Also irqs are disabled to avoid confusion due to interrupt handlers * invoking call_rcu(). */static int rcu_qsctr_help(struct rcu_ctrlblk *rcp){	if (rcp->rcucblist != NULL &&	    rcp->donetail != rcp->curtail) {		rcp->donetail = rcp->curtail;		return 1;	} 	return 0;} /* * Record an rcu quiescent state.  And an rcu_bh quiescent state while we * are at it, given that any rcu quiescent state is also an rcu_bh * quiescent state.  Use "+" instead of "||" to defeat short circuiting. */void rcu_sched_qs(int cpu){	unsigned long flags; 	local_irq_save(flags);	if (rcu_qsctr_help(&rcu_sched_ctrlblk) +	    rcu_qsctr_help(&rcu_bh_ctrlblk))		invoke_rcu_callbacks();	local_irq_restore(flags);} /* * Record an rcu_bh quiescent state. */void rcu_bh_qs(int cpu){	unsigned long flags; 	local_irq_save(flags);	if (rcu_qsctr_help(&rcu_bh_ctrlblk))		invoke_rcu_callbacks();	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. */void rcu_check_callbacks(int cpu, int user){	if (user ||	    (idle_cpu(cpu) &&	     !in_softirq() &&	     hardirq_count() <= (1 << HARDIRQ_SHIFT)))		rcu_sched_qs(cpu);	else if (!in_softirq())		rcu_bh_qs(cpu);	rcu_preempt_check_callbacks();} /* * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure * whose grace period has elapsed. */static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp){	char *rn = NULL;	struct rcu_head *next, *list;	unsigned long flags;	RCU_TRACE(int cb_count = 0); 	/* If no RCU callbacks ready to invoke, just return. */	if (&rcp->rcucblist == rcp->donetail) {		RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));		RCU_TRACE(trace_rcu_batch_end(rcp->name, 0));		return;	} 	/* Move the ready-to-invoke callbacks to a local list. */	local_irq_save(flags);	RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));	list = rcp->rcucblist;	rcp->rcucblist = *rcp->donetail;	*rcp->donetail = NULL;	if (rcp->curtail == rcp->donetail)		rcp->curtail = &rcp->rcucblist;	rcu_preempt_remove_callbacks(rcp);	rcp->donetail = &rcp->rcucblist;	local_irq_restore(flags); 	/* Invoke the callbacks on the local list. */	RCU_TRACE(rn = rcp->name);	while (list) {		next = list->next;		prefetch(next);		debug_rcu_head_unqueue(list);		local_bh_disable();		__rcu_reclaim(rn, list);		local_bh_enable();		list = next;		RCU_TRACE(cb_count++);	}	RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));	RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count));} static void rcu_process_callbacks(struct softirq_action *unused){	__rcu_process_callbacks(&rcu_sched_ctrlblk);	__rcu_process_callbacks(&rcu_bh_ctrlblk);	rcu_preempt_process_callbacks();} /* * Wait for a grace period to elapse.  But it is illegal to invoke * synchronize_sched() from within an RCU read-side critical section. * Therefore, any legal call to synchronize_sched() is a quiescent * state, and so on a UP system, synchronize_sched() need do nothing. * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the * benefits of doing might_sleep() to reduce latency.) * * Cool, huh?  (Due to Josh Triplett.) * * But we want to make this a static inline later.  The cond_resched() * currently makes this problematic. */void synchronize_sched(void){	cond_resched();}EXPORT_SYMBOL_GPL(synchronize_sched); /* * Helper function for call_rcu() and call_rcu_bh(). */static void __call_rcu(struct rcu_head *head,		       void (*func)(struct rcu_head *rcu),		       struct rcu_ctrlblk *rcp){	unsigned long flags; 	debug_rcu_head_queue(head);	head->func = func;	head->next = NULL; 	local_irq_save(flags);	*rcp->curtail = head;	rcp->curtail = &head->next;	RCU_TRACE(rcp->qlen++);	local_irq_restore(flags);} /* * Post an RCU callback to be invoked after the end of an RCU-sched grace * period.  But since we have but one CPU, that would be after any * quiescent state. */void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu)){	__call_rcu(head, func, &rcu_sched_ctrlblk);}EXPORT_SYMBOL_GPL(call_rcu_sched); /* * Post an RCU bottom-half callback to be invoked after any subsequent * quiescent state. */void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu)){	__call_rcu(head, func, &rcu_bh_ctrlblk);}EXPORT_SYMBOL_GPL(call_rcu_bh);