/* * 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/moduleparam.h>#include <linux/completion.h>#include <linux/interrupt.h>#include <linux/notifier.h>#include <linux/rcupdate.h>#include <linux/kernel.h>#include <linux/module.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> /* Controls for rcu_kthread() kthread, replacing RCU_SOFTIRQ used previously. */static struct task_struct *rcu_kthread_task;static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq);static unsigned long have_rcu_kthread_work; /* Forward declarations for rcutiny_plugin.h. */struct rcu_ctrlblk;static void invoke_rcu_kthread(void);static void rcu_process_callbacks(struct rcu_ctrlblk *rcp);static int rcu_kthread(void *arg);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;} /* * Wake up rcu_kthread() to process callbacks now eligible for invocation * or to boost readers. */static void invoke_rcu_kthread(void){	have_rcu_kthread_work = 1;	wake_up(&rcu_kthread_wq);} /* * 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_kthread();	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_kthread();	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){	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)		return; 	/* Move the ready-to-invoke callbacks to a local list. */	local_irq_save(flags);	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. */	while (list) {		next = list->next;		prefetch(next);		debug_rcu_head_unqueue(list);		local_bh_disable();		__rcu_reclaim(list);		local_bh_enable();		list = next;		RCU_TRACE(cb_count++);	}	RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));} /* * This kthread invokes RCU callbacks whose grace periods have * elapsed.  It is awakened as needed, and takes the place of the * RCU_SOFTIRQ that was used previously for this purpose. * This is a kthread, but it is never stopped, at least not until * the system goes down. */static int rcu_kthread(void *arg){	unsigned long work;	unsigned long morework;	unsigned long flags; 	for (;;) {		wait_event_interruptible(rcu_kthread_wq,					 have_rcu_kthread_work != 0);		morework = rcu_boost();		local_irq_save(flags);		work = have_rcu_kthread_work;		have_rcu_kthread_work = morework;		local_irq_restore(flags);		if (work) {			rcu_process_callbacks(&rcu_sched_ctrlblk);			rcu_process_callbacks(&rcu_bh_ctrlblk);			rcu_preempt_process_callbacks();		}		schedule_timeout_interruptible(1); /* Leave CPU for others. */	} 	return 0;  /* Not reached, but needed to shut gcc up. */} /* * 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); void rcu_barrier_bh(void){	struct rcu_synchronize rcu; 	init_rcu_head_on_stack(&rcu.head);	init_completion(&rcu.completion);	/* Will wake me after RCU finished. */	call_rcu_bh(&rcu.head, wakeme_after_rcu);	/* Wait for it. */	wait_for_completion(&rcu.completion);	destroy_rcu_head_on_stack(&rcu.head);}EXPORT_SYMBOL_GPL(rcu_barrier_bh); void rcu_barrier_sched(void){	struct rcu_synchronize rcu; 	init_rcu_head_on_stack(&rcu.head);	init_completion(&rcu.completion);	/* Will wake me after RCU finished. */	call_rcu_sched(&rcu.head, wakeme_after_rcu);	/* Wait for it. */	wait_for_completion(&rcu.completion);	destroy_rcu_head_on_stack(&rcu.head);}EXPORT_SYMBOL_GPL(rcu_barrier_sched); /* * Spawn the kthread that invokes RCU callbacks. */static int __init rcu_spawn_kthreads(void){	struct sched_param sp; 	rcu_kthread_task = kthread_run(rcu_kthread, NULL, "rcu_kthread");	sp.sched_priority = RCU_BOOST_PRIO;	sched_setscheduler_nocheck(rcu_kthread_task, SCHED_FIFO, &sp);	return 0;}early_initcall(rcu_spawn_kthreads);