kernel/rcu/update.c - maze/linux - Git at Google

 /*
  * 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, you can access it online at
  * http://www.gnu.org/licenses/gpl-2.0.html.
  *
  * 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 <linux/atomic.h>
 #include <linux/bitops.h>
 #include <linux/percpu.h>
 #include <linux/notifier.h>
 #include <linux/cpu.h>
 #include <linux/mutex.h>
 #include <linux/export.h>
 #include <linux/hardirq.h>
 #include <linux/delay.h>
 #include <linux/module.h>

 #define CREATE_TRACE_POINTS

 #include "rcu.h"

 MODULE_ALIAS("rcupdate");
 #ifdef MODULE_PARAM_PREFIX
 #undef MODULE_PARAM_PREFIX
 #endif
 #define MODULE_PARAM_PREFIX "rcupdate."

 module_param(rcu_expedited, int, 0);

 #ifdef CONFIG_PREEMPT_RCU

 /*
  * Preemptible RCU implementation for rcu_read_lock().
  * Just increment ->rcu_read_lock_nesting, shared state will be updated
  * if we block.
  */
 void __rcu_read_lock(void)
 {
 	current->rcu_read_lock_nesting++;
 	barrier();  /* critical section after entry code. */
 }
 EXPORT_SYMBOL_GPL(__rcu_read_lock);

 /*
  * Preemptible RCU implementation for rcu_read_unlock().
  * Decrement ->rcu_read_lock_nesting.  If the result is zero (outermost
  * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
  * invoke rcu_read_unlock_special() to clean up after a context switch
  * in an RCU read-side critical section and other special cases.
  */
 void __rcu_read_unlock(void)
 {
 	struct task_struct *t = current;

 	if (t->rcu_read_lock_nesting != 1) {
 		--t->rcu_read_lock_nesting;
 	} else {
 		barrier();  /* critical section before exit code. */
 		t->rcu_read_lock_nesting = INT_MIN;
 #ifdef CONFIG_PROVE_RCU_DELAY
 		udelay(10); /* Make preemption more probable. */
 #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
 		barrier();  /* assign before ->rcu_read_unlock_special load */
 		if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
 			rcu_read_unlock_special(t);
 		barrier();  /* ->rcu_read_unlock_special load before assign */
 		t->rcu_read_lock_nesting = 0;
 	}
 #ifdef CONFIG_PROVE_LOCKING
 	{
 		int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);

 		WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
 	}
 #endif /* #ifdef CONFIG_PROVE_LOCKING */
 }
 EXPORT_SYMBOL_GPL(__rcu_read_unlock);

 #endif /* #ifdef CONFIG_PREEMPT_RCU */

 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 static struct lock_class_key rcu_lock_key;
 struct lockdep_map rcu_lock_map =
 	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
 EXPORT_SYMBOL_GPL(rcu_lock_map);

 static struct lock_class_key rcu_bh_lock_key;
 struct lockdep_map rcu_bh_lock_map =
 	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
 EXPORT_SYMBOL_GPL(rcu_bh_lock_map);

 static struct lock_class_key rcu_sched_lock_key;
 struct lockdep_map rcu_sched_lock_map =
 	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
 EXPORT_SYMBOL_GPL(rcu_sched_lock_map);

 static struct lock_class_key rcu_callback_key;
 struct lockdep_map rcu_callback_map =
 	STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key);
 EXPORT_SYMBOL_GPL(rcu_callback_map);

 int notrace debug_lockdep_rcu_enabled(void)
 {
 	return rcu_scheduler_active && debug_locks &&
 	       current->lockdep_recursion == 0;
 }
 EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);

 /**
  * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
  *
  * Check for bottom half being disabled, which covers both the
  * CONFIG_PROVE_RCU and not cases.  Note that if someone uses
  * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
  * will show the situation.  This is useful for debug checks in functions
  * that require that they be called within an RCU read-side critical
  * section.
  *
  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
  *
  * Note that rcu_read_lock() is disallowed if the CPU is either idle or
  * offline from an RCU perspective, so check for those as well.
  */
 int rcu_read_lock_bh_held(void)
 {
 	if (!debug_lockdep_rcu_enabled())
 		return 1;
 	if (!rcu_is_watching())
 		return 0;
 	if (!rcu_lockdep_current_cpu_online())
 		return 0;
 	return in_softirq() || irqs_disabled();
 }
 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);

 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

 struct rcu_synchronize {
 	struct rcu_head head;
 	struct completion 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);
 }

 void wait_rcu_gp(call_rcu_func_t crf)
 {
 	struct rcu_synchronize rcu;

 	init_rcu_head_on_stack(&rcu.head);
 	init_completion(&rcu.completion);
 	/* Will wake me after RCU finished. */
 	crf(&rcu.head, wakeme_after_rcu);
 	/* Wait for it. */
 	wait_for_completion(&rcu.completion);
 	destroy_rcu_head_on_stack(&rcu.head);
 }
 EXPORT_SYMBOL_GPL(wait_rcu_gp);

 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
 static inline void debug_init_rcu_head(struct rcu_head *head)
 {
 	debug_object_init(head, &rcuhead_debug_descr);
 }

 static inline void debug_rcu_head_free(struct rcu_head *head)
 {
 	debug_object_free(head, &rcuhead_debug_descr);
 }

 /*
  * fixup_activate is called when:
  * - an active object is activated
  * - an unknown object is activated (might be a statically initialized object)
  * Activation is performed internally by call_rcu().
  */
 static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
 {
 	struct rcu_head *head = addr;

 	switch (state) {

 	case ODEBUG_STATE_NOTAVAILABLE:
 		/*
 		 * This is not really a fixup. We just make sure that it is
 		 * tracked in the object tracker.
 		 */
 		debug_object_init(head, &rcuhead_debug_descr);
 		debug_object_activate(head, &rcuhead_debug_descr);
 		return 0;
 	default:
 		return 1;
 	}
 }

 /**
  * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
  * @head: pointer to rcu_head structure to be initialized
  *
  * This function informs debugobjects of a new rcu_head structure that
  * has been allocated as an auto variable on the stack.  This function
  * is not required for rcu_head structures that are statically defined or
  * that are dynamically allocated on the heap.  This function has no
  * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
  */
 void init_rcu_head_on_stack(struct rcu_head *head)
 {
 	debug_object_init_on_stack(head, &rcuhead_debug_descr);
 }
 EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);

 /**
  * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
  * @head: pointer to rcu_head structure to be initialized
  *
  * This function informs debugobjects that an on-stack rcu_head structure
  * is about to go out of scope.  As with init_rcu_head_on_stack(), this
  * function is not required for rcu_head structures that are statically
  * defined or that are dynamically allocated on the heap.  Also as with
  * init_rcu_head_on_stack(), this function has no effect for
  * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
  */
 void destroy_rcu_head_on_stack(struct rcu_head *head)
 {
 	debug_object_free(head, &rcuhead_debug_descr);
 }
 EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);

 struct debug_obj_descr rcuhead_debug_descr = {
 	.name = "rcu_head",
 	.fixup_activate = rcuhead_fixup_activate,
 };
 EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */

 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
 void do_trace_rcu_torture_read(const char *rcutorturename, struct rcu_head *rhp,
 			       unsigned long secs,
 			       unsigned long c_old, unsigned long c)
 {
 	trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c);
 }
 EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
 #else
 #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
 	do { } while (0)
 #endif

 #ifdef CONFIG_RCU_STALL_COMMON

 #ifdef CONFIG_PROVE_RCU
 #define RCU_STALL_DELAY_DELTA	       (5 * HZ)
 #else
 #define RCU_STALL_DELAY_DELTA	       0
 #endif

 int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
 static int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;

 module_param(rcu_cpu_stall_suppress, int, 0644);
 module_param(rcu_cpu_stall_timeout, int, 0644);

 int rcu_jiffies_till_stall_check(void)
 {
 	int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout);

 	/*
 	 * Limit check must be consistent with the Kconfig limits
 	 * for CONFIG_RCU_CPU_STALL_TIMEOUT.
 	 */
 	if (till_stall_check < 3) {
 		ACCESS_ONCE(rcu_cpu_stall_timeout) = 3;
 		till_stall_check = 3;
 	} else if (till_stall_check > 300) {
 		ACCESS_ONCE(rcu_cpu_stall_timeout) = 300;
 		till_stall_check = 300;
 	}
 	return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
 }

 static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
 {
 	rcu_cpu_stall_suppress = 1;
 	return NOTIFY_DONE;
 }

 static struct notifier_block rcu_panic_block = {
 	.notifier_call = rcu_panic,
 };

 static int __init check_cpu_stall_init(void)
 {
 	atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
 	return 0;
 }
 early_initcall(check_cpu_stall_init);

 #endif /* #ifdef CONFIG_RCU_STALL_COMMON */
	/*
	* 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, you can access it online at
	* http://www.gnu.org/licenses/gpl-2.0.html.
	*
	* 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 <linux/atomic.h>
	#include <linux/bitops.h>
	#include <linux/percpu.h>
	#include <linux/notifier.h>
	#include <linux/cpu.h>
	#include <linux/mutex.h>
	#include <linux/export.h>
	#include <linux/hardirq.h>
	#include <linux/delay.h>
	#include <linux/module.h>

	#define CREATE_TRACE_POINTS

	#include "rcu.h"

	MODULE_ALIAS("rcupdate");
	#ifdef MODULE_PARAM_PREFIX
	#undef MODULE_PARAM_PREFIX
	#endif
	#define MODULE_PARAM_PREFIX "rcupdate."

	module_param(rcu_expedited, int, 0);

	#ifdef CONFIG_PREEMPT_RCU

	/*
	* Preemptible RCU implementation for rcu_read_lock().
	* Just increment ->rcu_read_lock_nesting, shared state will be updated
	* if we block.
	*/
	void __rcu_read_lock(void)
	{
	current->rcu_read_lock_nesting++;
	barrier(); /* critical section after entry code. */
	}
	EXPORT_SYMBOL_GPL(__rcu_read_lock);

	/*
	* Preemptible RCU implementation for rcu_read_unlock().
	* Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
	* rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
	* invoke rcu_read_unlock_special() to clean up after a context switch
	* in an RCU read-side critical section and other special cases.
	*/
	void __rcu_read_unlock(void)
	{
	struct task_struct *t = current;

	if (t->rcu_read_lock_nesting != 1) {
	--t->rcu_read_lock_nesting;
	} else {
	barrier(); /* critical section before exit code. */
	t->rcu_read_lock_nesting = INT_MIN;
	#ifdef CONFIG_PROVE_RCU_DELAY
	udelay(10); /* Make preemption more probable. */
	#endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
	barrier(); /* assign before ->rcu_read_unlock_special load */
	if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
	rcu_read_unlock_special(t);
	barrier(); /* ->rcu_read_unlock_special load before assign */
	t->rcu_read_lock_nesting = 0;
	}
	#ifdef CONFIG_PROVE_LOCKING
	{
	int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);

	WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
	}
	#endif /* #ifdef CONFIG_PROVE_LOCKING */
	}
	EXPORT_SYMBOL_GPL(__rcu_read_unlock);

	#endif /* #ifdef CONFIG_PREEMPT_RCU */

	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	static struct lock_class_key rcu_lock_key;
	struct lockdep_map rcu_lock_map =
	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
	EXPORT_SYMBOL_GPL(rcu_lock_map);

	static struct lock_class_key rcu_bh_lock_key;
	struct lockdep_map rcu_bh_lock_map =
	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
	EXPORT_SYMBOL_GPL(rcu_bh_lock_map);

	static struct lock_class_key rcu_sched_lock_key;
	struct lockdep_map rcu_sched_lock_map =
	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
	EXPORT_SYMBOL_GPL(rcu_sched_lock_map);

	static struct lock_class_key rcu_callback_key;
	struct lockdep_map rcu_callback_map =
	STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key);
	EXPORT_SYMBOL_GPL(rcu_callback_map);

	int notrace debug_lockdep_rcu_enabled(void)
	{
	return rcu_scheduler_active && debug_locks &&
	current->lockdep_recursion == 0;
	}
	EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);

	/**
	* rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
	*
	* Check for bottom half being disabled, which covers both the
	* CONFIG_PROVE_RCU and not cases. Note that if someone uses
	* rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
	* will show the situation. This is useful for debug checks in functions
	* that require that they be called within an RCU read-side critical
	* section.
	*
	* Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
	*
	* Note that rcu_read_lock() is disallowed if the CPU is either idle or
	* offline from an RCU perspective, so check for those as well.
	*/
	int rcu_read_lock_bh_held(void)
	{
	if (!debug_lockdep_rcu_enabled())
	return 1;
	if (!rcu_is_watching())
	return 0;
	if (!rcu_lockdep_current_cpu_online())
	return 0;
	return in_softirq() \|\| irqs_disabled();
	}
	EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);

	#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

	struct rcu_synchronize {
	struct rcu_head head;
	struct completion 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);
	}

	void wait_rcu_gp(call_rcu_func_t crf)
	{
	struct rcu_synchronize rcu;

	init_rcu_head_on_stack(&rcu.head);
	init_completion(&rcu.completion);
	/* Will wake me after RCU finished. */
	crf(&rcu.head, wakeme_after_rcu);
	/* Wait for it. */
	wait_for_completion(&rcu.completion);
	destroy_rcu_head_on_stack(&rcu.head);
	}
	EXPORT_SYMBOL_GPL(wait_rcu_gp);

	#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
	static inline void debug_init_rcu_head(struct rcu_head *head)
	{
	debug_object_init(head, &rcuhead_debug_descr);
	}

	static inline void debug_rcu_head_free(struct rcu_head *head)
	{
	debug_object_free(head, &rcuhead_debug_descr);
	}

	/*
	* fixup_activate is called when:
	* - an active object is activated
	* - an unknown object is activated (might be a statically initialized object)
	* Activation is performed internally by call_rcu().
	*/
	static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
	{
	struct rcu_head *head = addr;

	switch (state) {

	case ODEBUG_STATE_NOTAVAILABLE:
	/*
	* This is not really a fixup. We just make sure that it is
	* tracked in the object tracker.
	*/
	debug_object_init(head, &rcuhead_debug_descr);
	debug_object_activate(head, &rcuhead_debug_descr);
	return 0;
	default:
	return 1;
	}
	}

	/**
	* init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
	* @head: pointer to rcu_head structure to be initialized
	*
	* This function informs debugobjects of a new rcu_head structure that
	* has been allocated as an auto variable on the stack. This function
	* is not required for rcu_head structures that are statically defined or
	* that are dynamically allocated on the heap. This function has no
	* effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
	*/
	void init_rcu_head_on_stack(struct rcu_head *head)
	{
	debug_object_init_on_stack(head, &rcuhead_debug_descr);
	}
	EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);

	/**
	* destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
	* @head: pointer to rcu_head structure to be initialized
	*
	* This function informs debugobjects that an on-stack rcu_head structure
	* is about to go out of scope. As with init_rcu_head_on_stack(), this
	* function is not required for rcu_head structures that are statically
	* defined or that are dynamically allocated on the heap. Also as with
	* init_rcu_head_on_stack(), this function has no effect for
	* !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
	*/
	void destroy_rcu_head_on_stack(struct rcu_head *head)
	{
	debug_object_free(head, &rcuhead_debug_descr);
	}
	EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);

	struct debug_obj_descr rcuhead_debug_descr = {
	.name = "rcu_head",
	.fixup_activate = rcuhead_fixup_activate,
	};
	EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
	#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */

	#if defined(CONFIG_TREE_RCU) \|\| defined(CONFIG_TREE_PREEMPT_RCU) \|\| defined(CONFIG_RCU_TRACE)
	void do_trace_rcu_torture_read(const char rcutorturename, struct rcu_head rhp,
	unsigned long secs,
	unsigned long c_old, unsigned long c)
	{
	trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c);
	}
	EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
	#else
	#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
	do { } while (0)
	#endif

	#ifdef CONFIG_RCU_STALL_COMMON

	#ifdef CONFIG_PROVE_RCU
	#define RCU_STALL_DELAY_DELTA (5 * HZ)
	#else
	#define RCU_STALL_DELAY_DELTA 0
	#endif

	int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
	static int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;

	module_param(rcu_cpu_stall_suppress, int, 0644);
	module_param(rcu_cpu_stall_timeout, int, 0644);

	int rcu_jiffies_till_stall_check(void)
	{
	int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout);

	/*
	* Limit check must be consistent with the Kconfig limits
	* for CONFIG_RCU_CPU_STALL_TIMEOUT.
	*/
	if (till_stall_check < 3) {
	ACCESS_ONCE(rcu_cpu_stall_timeout) = 3;
	till_stall_check = 3;
	} else if (till_stall_check > 300) {
	ACCESS_ONCE(rcu_cpu_stall_timeout) = 300;
	till_stall_check = 300;
	}
	return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
	}

	static int rcu_panic(struct notifier_block this, unsigned long ev, void ptr)
	{
	rcu_cpu_stall_suppress = 1;
	return NOTIFY_DONE;
	}

	static struct notifier_block rcu_panic_block = {
	.notifier_call = rcu_panic,
	};

	static int __init check_cpu_stall_init(void)
	{
	atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
	return 0;
	}
	early_initcall(check_cpu_stall_init);

	#endif /* #ifdef CONFIG_RCU_STALL_COMMON */