kernel/rcutiny.c - arm/linux - Git at Google

 /*
  * 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);

 static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;

 #include "rcutiny_plugin.h"

 /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
 static void rcu_idle_enter_common(long long newval)
 {
 	if (newval) {
 		RCU_TRACE(trace_rcu_dyntick("--=",
 					    rcu_dynticks_nesting, newval));
 		rcu_dynticks_nesting = newval;
 		return;
 	}
 	RCU_TRACE(trace_rcu_dyntick("Start", rcu_dynticks_nesting, newval));
 	if (!is_idle_task(current)) {
 		struct task_struct *idle = idle_task(smp_processor_id());

 		RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task",
 					    rcu_dynticks_nesting, newval));
 		ftrace_dump(DUMP_ALL);
 		WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
 			  current->pid, current->comm,
 			  idle->pid, idle->comm); /* must be idle task! */
 	}
 	rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
 	barrier();
 	rcu_dynticks_nesting = newval;
 }

 /*
  * Enter idle, 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_idle_enter(void)
 {
 	unsigned long flags;
 	long long newval;

 	local_irq_save(flags);
 	WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
 	if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) ==
 	    DYNTICK_TASK_NEST_VALUE)
 		newval = 0;
 	else
 		newval = rcu_dynticks_nesting - DYNTICK_TASK_NEST_VALUE;
 	rcu_idle_enter_common(newval);
 	local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(rcu_idle_enter);

 /*
  * Exit an interrupt handler towards idle.
  */
 void rcu_irq_exit(void)
 {
 	unsigned long flags;
 	long long newval;

 	local_irq_save(flags);
 	newval = rcu_dynticks_nesting - 1;
 	WARN_ON_ONCE(newval < 0);
 	rcu_idle_enter_common(newval);
 	local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(rcu_irq_exit);

 /* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */
 static void rcu_idle_exit_common(long long oldval)
 {
 	if (oldval) {
 		RCU_TRACE(trace_rcu_dyntick("++=",
 					    oldval, rcu_dynticks_nesting));
 		return;
 	}
 	RCU_TRACE(trace_rcu_dyntick("End", oldval, rcu_dynticks_nesting));
 	if (!is_idle_task(current)) {
 		struct task_struct *idle = idle_task(smp_processor_id());

 		RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task",
 			  oldval, rcu_dynticks_nesting));
 		ftrace_dump(DUMP_ALL);
 		WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
 			  current->pid, current->comm,
 			  idle->pid, idle->comm); /* must be idle task! */
 	}
 }

 /*
  * Exit idle, so that we are no longer in an extended quiescent state.
  */
 void rcu_idle_exit(void)
 {
 	unsigned long flags;
 	long long oldval;

 	local_irq_save(flags);
 	oldval = rcu_dynticks_nesting;
 	WARN_ON_ONCE(rcu_dynticks_nesting < 0);
 	if (rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK)
 		rcu_dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
 	else
 		rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
 	rcu_idle_exit_common(oldval);
 	local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(rcu_idle_exit);

 /*
  * Enter an interrupt handler, moving away from idle.
  */
 void rcu_irq_enter(void)
 {
 	unsigned long flags;
 	long long oldval;

 	local_irq_save(flags);
 	oldval = rcu_dynticks_nesting;
 	rcu_dynticks_nesting++;
 	WARN_ON_ONCE(rcu_dynticks_nesting == 0);
 	rcu_idle_exit_common(oldval);
 	local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(rcu_irq_enter);

 #ifdef CONFIG_DEBUG_LOCK_ALLOC

 /*
  * Test whether RCU thinks that the current CPU is idle.
  */
 int rcu_is_cpu_idle(void)
 {
 	return !rcu_dynticks_nesting;
 }
 EXPORT_SYMBOL(rcu_is_cpu_idle);

 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

 /*
  * Test whether the current CPU was interrupted from idle.  Nested
  * interrupts don't count, we must be running at the first interrupt
  * level.
  */
 static int rcu_is_cpu_rrupt_from_idle(void)
 {
 	return rcu_dynticks_nesting <= 1;
 }

 /*
  * 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)
 {
 	reset_cpu_stall_ticks(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.  This function must
  * be called from hardirq context.  It is normally called from the
  * scheduling-clock interrupt.
  */
 void rcu_check_callbacks(int cpu, int user)
 {
 	check_cpu_stalls();
 	if (user || rcu_is_cpu_rrupt_from_idle())
 		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, 0, -1));
 		RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
 					      ACCESS_ONCE(rcp->rcucblist),
 					      need_resched(),
 					      is_idle_task(current),
 					      rcu_is_callbacks_kthread()));
 		return;
 	}

 	/* Move the ready-to-invoke callbacks to a local list. */
 	local_irq_save(flags);
 	RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -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, 0, need_resched(),
 				      is_idle_task(current),
 				      rcu_is_callbacks_kthread()));
 }

 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)
 {
 	rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
 			   !lock_is_held(&rcu_lock_map) &&
 			   !lock_is_held(&rcu_sched_lock_map),
 			   "Illegal synchronize_sched() in RCU read-side critical section");
 	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);
	/*
	* 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);

	static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;

	#include "rcutiny_plugin.h"

	/* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
	static void rcu_idle_enter_common(long long newval)
	{
	if (newval) {
	RCU_TRACE(trace_rcu_dyntick("--=",
	rcu_dynticks_nesting, newval));
	rcu_dynticks_nesting = newval;
	return;
	}
	RCU_TRACE(trace_rcu_dyntick("Start", rcu_dynticks_nesting, newval));
	if (!is_idle_task(current)) {
	struct task_struct *idle = idle_task(smp_processor_id());

	RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task",
	rcu_dynticks_nesting, newval));
	ftrace_dump(DUMP_ALL);
	WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
	current->pid, current->comm,
	idle->pid, idle->comm); /* must be idle task! */
	}
	rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
	barrier();
	rcu_dynticks_nesting = newval;
	}

	/*
	* Enter idle, 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_idle_enter(void)
	{
	unsigned long flags;
	long long newval;

	local_irq_save(flags);
	WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
	if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) ==
	DYNTICK_TASK_NEST_VALUE)
	newval = 0;
	else
	newval = rcu_dynticks_nesting - DYNTICK_TASK_NEST_VALUE;
	rcu_idle_enter_common(newval);
	local_irq_restore(flags);
	}
	EXPORT_SYMBOL_GPL(rcu_idle_enter);

	/*
	* Exit an interrupt handler towards idle.
	*/
	void rcu_irq_exit(void)
	{
	unsigned long flags;
	long long newval;

	local_irq_save(flags);
	newval = rcu_dynticks_nesting - 1;
	WARN_ON_ONCE(newval < 0);
	rcu_idle_enter_common(newval);
	local_irq_restore(flags);
	}
	EXPORT_SYMBOL_GPL(rcu_irq_exit);

	/* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */
	static void rcu_idle_exit_common(long long oldval)
	{
	if (oldval) {
	RCU_TRACE(trace_rcu_dyntick("++=",
	oldval, rcu_dynticks_nesting));
	return;
	}
	RCU_TRACE(trace_rcu_dyntick("End", oldval, rcu_dynticks_nesting));
	if (!is_idle_task(current)) {
	struct task_struct *idle = idle_task(smp_processor_id());

	RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task",
	oldval, rcu_dynticks_nesting));
	ftrace_dump(DUMP_ALL);
	WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
	current->pid, current->comm,
	idle->pid, idle->comm); /* must be idle task! */
	}
	}

	/*
	* Exit idle, so that we are no longer in an extended quiescent state.
	*/
	void rcu_idle_exit(void)
	{
	unsigned long flags;
	long long oldval;

	local_irq_save(flags);
	oldval = rcu_dynticks_nesting;
	WARN_ON_ONCE(rcu_dynticks_nesting < 0);
	if (rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK)
	rcu_dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
	else
	rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
	rcu_idle_exit_common(oldval);
	local_irq_restore(flags);
	}
	EXPORT_SYMBOL_GPL(rcu_idle_exit);

	/*
	* Enter an interrupt handler, moving away from idle.
	*/
	void rcu_irq_enter(void)
	{
	unsigned long flags;
	long long oldval;

	local_irq_save(flags);
	oldval = rcu_dynticks_nesting;
	rcu_dynticks_nesting++;
	WARN_ON_ONCE(rcu_dynticks_nesting == 0);
	rcu_idle_exit_common(oldval);
	local_irq_restore(flags);
	}
	EXPORT_SYMBOL_GPL(rcu_irq_enter);

	#ifdef CONFIG_DEBUG_LOCK_ALLOC

	/*
	* Test whether RCU thinks that the current CPU is idle.
	*/
	int rcu_is_cpu_idle(void)
	{
	return !rcu_dynticks_nesting;
	}
	EXPORT_SYMBOL(rcu_is_cpu_idle);

	#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

	/*
	* Test whether the current CPU was interrupted from idle. Nested
	* interrupts don't count, we must be running at the first interrupt
	* level.
	*/
	static int rcu_is_cpu_rrupt_from_idle(void)
	{
	return rcu_dynticks_nesting <= 1;
	}

	/*
	* 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)
	{
	reset_cpu_stall_ticks(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. This function must
	* be called from hardirq context. It is normally called from the
	* scheduling-clock interrupt.
	*/
	void rcu_check_callbacks(int cpu, int user)
	{
	check_cpu_stalls();
	if (user \|\| rcu_is_cpu_rrupt_from_idle())
	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, 0, -1));
	RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
	ACCESS_ONCE(rcp->rcucblist),
	need_resched(),
	is_idle_task(current),
	rcu_is_callbacks_kthread()));
	return;
	}

	/* Move the ready-to-invoke callbacks to a local list. */
	local_irq_save(flags);
	RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -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, 0, need_resched(),
	is_idle_task(current),
	rcu_is_callbacks_kthread()));
	}

	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)
	{
	rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
	!lock_is_held(&rcu_lock_map) &&
	!lock_is_held(&rcu_sched_lock_map),
	"Illegal synchronize_sched() in RCU read-side critical section");
	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);