[mirror_ubuntu-artful-kernel.git] / kernel / rcupdate.c

/*
 * 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, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * 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 <trace/events/rcu.h>

#include "rcu.h"

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);

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_cpu_idle())
		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_PROVE_RCU
/*
 * wrapper function to avoid #include problems.
 */
int rcu_my_thread_group_empty(void)
{
	return thread_group_empty(current);
}
EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
#endif /* #ifdef CONFIG_PROVE_RCU */

#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. */
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 */
Commit	Line	Data
1da177e4 LT	1	/*
	2	* Read-Copy Update mechanism for mutual exclusion
	3	*
	4	* This program is free software; you can redistribute it and/or modify
	5	* it under the terms of the GNU General Public License as published by
	6	* the Free Software Foundation; either version 2 of the License, or
	7	* (at your option) any later version.
	8	*
	9	* This program is distributed in the hope that it will be useful,
	10	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	11	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	12	* GNU General Public License for more details.
	13	*
	14	* You should have received a copy of the GNU General Public License
	15	* along with this program; if not, write to the Free Software
	16	* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
	17	*
01c1c660	18	* Copyright IBM Corporation, 2001
1da177e4 LT	19	*
	20	* Authors: Dipankar Sarma <dipankar@in.ibm.com>
	21	* Manfred Spraul <manfred@colorfullife.com>
a71fca58	22	*
1da177e4 LT	23	* Based on the original work by Paul McKenney <paulmck@us.ibm.com>
	24	* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
	25	* Papers:
	26	* http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
	27	* http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
	28	*
	29	* For detailed explanation of Read-Copy Update mechanism see -
a71fca58	30	* http://lse.sourceforge.net/locking/rcupdate.html
1da177e4 LT	31	*
	32	*/
	33	#include <linux/types.h>
	34	#include <linux/kernel.h>
	35	#include <linux/init.h>
	36	#include <linux/spinlock.h>
	37	#include <linux/smp.h>
	38	#include <linux/interrupt.h>
	39	#include <linux/sched.h>
60063497	40	#include <linux/atomic.h>
1da177e4	41	#include <linux/bitops.h>
1da177e4 LT	42	#include <linux/percpu.h>
1da177e4 LT	43	#include <linux/notifier.h>
1da177e4	44	#include <linux/cpu.h>
9331b315	45	#include <linux/mutex.h>
9984de1a	46	#include <linux/export.h>
e3818b8d	47	#include <linux/hardirq.h>
e3ebfb96	48	#include <linux/delay.h>
3705b88d	49	#include <linux/module.h>
1da177e4	50
29c00b4a PM	51	#define CREATE_TRACE_POINTS
	52	#include <trace/events/rcu.h>
	53
	54	#include "rcu.h"
	55
3705b88d AM	56	module_param(rcu_expedited, int, 0);
3705b88d AM	57
9dd8fb16 PM	58	#ifdef CONFIG_PREEMPT_RCU
9dd8fb16 PM	59
2a3fa843 PM	60	/*
	61	* Preemptible RCU implementation for rcu_read_lock().
	62	* Just increment ->rcu_read_lock_nesting, shared state will be updated
	63	* if we block.
	64	*/
	65	void __rcu_read_lock(void)
	66	{
	67	current->rcu_read_lock_nesting++;
	68	barrier(); /* critical section after entry code. */
	69	}
	70	EXPORT_SYMBOL_GPL(__rcu_read_lock);
	71
	72	/*
	73	* Preemptible RCU implementation for rcu_read_unlock().
	74	* Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
	75	* rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
	76	* invoke rcu_read_unlock_special() to clean up after a context switch
	77	* in an RCU read-side critical section and other special cases.
	78	*/
	79	void __rcu_read_unlock(void)
	80	{
	81	struct task_struct *t = current;
	82
	83	if (t->rcu_read_lock_nesting != 1) {
	84	--t->rcu_read_lock_nesting;
	85	} else {
	86	barrier(); /* critical section before exit code. */
	87	t->rcu_read_lock_nesting = INT_MIN;
e3ebfb96 PM	88	#ifdef CONFIG_PROVE_RCU_DELAY
	89	udelay(10); /* Make preemption more probable. */
	90	#endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
2a3fa843 PM	91	barrier(); /* assign before ->rcu_read_unlock_special load */
	92	if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
	93	rcu_read_unlock_special(t);
	94	barrier(); /* ->rcu_read_unlock_special load before assign */
	95	t->rcu_read_lock_nesting = 0;
	96	}
	97	#ifdef CONFIG_PROVE_LOCKING
	98	{
	99	int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
	100
	101	WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
	102	}
	103	#endif /* #ifdef CONFIG_PROVE_LOCKING */
	104	}
	105	EXPORT_SYMBOL_GPL(__rcu_read_unlock);
	106
2439b696	107	#endif /* #ifdef CONFIG_PREEMPT_RCU */
9dd8fb16	108
162cc279 PM	109	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	110	static struct lock_class_key rcu_lock_key;
	111	struct lockdep_map rcu_lock_map =
	112	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
	113	EXPORT_SYMBOL_GPL(rcu_lock_map);
632ee200 PM	114
	115	static struct lock_class_key rcu_bh_lock_key;
	116	struct lockdep_map rcu_bh_lock_map =
	117	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
	118	EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
	119
	120	static struct lock_class_key rcu_sched_lock_key;
	121	struct lockdep_map rcu_sched_lock_map =
	122	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
	123	EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
e3818b8d	124
a0a5a056	125	int notrace debug_lockdep_rcu_enabled(void)
bc293d62 PM	126	{
	127	return rcu_scheduler_active && debug_locks &&
	128	current->lockdep_recursion == 0;
	129	}
	130	EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
	131
e3818b8d	132	/**
ca5ecddf	133	* rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
e3818b8d PM	134	*
	135	* Check for bottom half being disabled, which covers both the
	136	* CONFIG_PROVE_RCU and not cases. Note that if someone uses
	137	* rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
ca5ecddf PM	138	* will show the situation. This is useful for debug checks in functions
	139	* that require that they be called within an RCU read-side critical
	140	* section.
e3818b8d PM	141	*
e3818b8d PM	142	* Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
c0d6d01b PM	143	*
	144	* Note that rcu_read_lock() is disallowed if the CPU is either idle or
	145	* offline from an RCU perspective, so check for those as well.
e3818b8d PM	146	*/
	147	int rcu_read_lock_bh_held(void)
	148	{
	149	if (!debug_lockdep_rcu_enabled())
	150	return 1;
e6b80a3b FW	151	if (rcu_is_cpu_idle())
e6b80a3b FW	152	return 0;
c0d6d01b PM	153	if (!rcu_lockdep_current_cpu_online())
c0d6d01b PM	154	return 0;
773e3f93	155	return in_softirq() \|\| irqs_disabled();
e3818b8d PM	156	}
	157	EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
	158
	159	#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
	160
2c42818e PM	161	struct rcu_synchronize {
	162	struct rcu_head head;
	163	struct completion completion;
	164	};
	165
fbf6bfca PM	166	/*
	167	* Awaken the corresponding synchronize_rcu() instance now that a
	168	* grace period has elapsed.
	169	*/
2c42818e	170	static void wakeme_after_rcu(struct rcu_head *head)
21a1ea9e	171	{
01c1c660 PM	172	struct rcu_synchronize *rcu;
	173
	174	rcu = container_of(head, struct rcu_synchronize, head);
	175	complete(&rcu->completion);
21a1ea9e	176	}
ee84b824	177
2c42818e PM	178	void wait_rcu_gp(call_rcu_func_t crf)
	179	{
	180	struct rcu_synchronize rcu;
	181
	182	init_rcu_head_on_stack(&rcu.head);
	183	init_completion(&rcu.completion);
	184	/* Will wake me after RCU finished. */
	185	crf(&rcu.head, wakeme_after_rcu);
	186	/* Wait for it. */
	187	wait_for_completion(&rcu.completion);
	188	destroy_rcu_head_on_stack(&rcu.head);
	189	}
	190	EXPORT_SYMBOL_GPL(wait_rcu_gp);
	191
ee84b824 PM	192	#ifdef CONFIG_PROVE_RCU
	193	/*
	194	* wrapper function to avoid #include problems.
	195	*/
	196	int rcu_my_thread_group_empty(void)
	197	{
	198	return thread_group_empty(current);
	199	}
	200	EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
	201	#endif /* #ifdef CONFIG_PROVE_RCU */
551d55a9 MD	202
	203	#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
	204	static inline void debug_init_rcu_head(struct rcu_head *head)
	205	{
	206	debug_object_init(head, &rcuhead_debug_descr);
	207	}
	208
	209	static inline void debug_rcu_head_free(struct rcu_head *head)
	210	{
	211	debug_object_free(head, &rcuhead_debug_descr);
	212	}
	213
551d55a9 MD	214	/*
	215	* fixup_activate is called when:
	216	* - an active object is activated
	217	* - an unknown object is activated (might be a statically initialized object)
	218	* Activation is performed internally by call_rcu().
	219	*/
	220	static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
	221	{
	222	struct rcu_head *head = addr;
	223
	224	switch (state) {
	225
	226	case ODEBUG_STATE_NOTAVAILABLE:
	227	/*
	228	* This is not really a fixup. We just make sure that it is
	229	* tracked in the object tracker.
	230	*/
	231	debug_object_init(head, &rcuhead_debug_descr);
	232	debug_object_activate(head, &rcuhead_debug_descr);
	233	return 0;
551d55a9	234	default:
551d55a9	235	return 1;
551d55a9 MD	236	}
	237	}
	238
	239	/**
	240	* init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
	241	* @head: pointer to rcu_head structure to be initialized
	242	*
	243	* This function informs debugobjects of a new rcu_head structure that
	244	* has been allocated as an auto variable on the stack. This function
	245	* is not required for rcu_head structures that are statically defined or
	246	* that are dynamically allocated on the heap. This function has no
	247	* effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
	248	*/
	249	void init_rcu_head_on_stack(struct rcu_head *head)
	250	{
	251	debug_object_init_on_stack(head, &rcuhead_debug_descr);
	252	}
	253	EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
	254
	255	/**
	256	* destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
	257	* @head: pointer to rcu_head structure to be initialized
	258	*
	259	* This function informs debugobjects that an on-stack rcu_head structure
	260	* is about to go out of scope. As with init_rcu_head_on_stack(), this
	261	* function is not required for rcu_head structures that are statically
	262	* defined or that are dynamically allocated on the heap. Also as with
	263	* init_rcu_head_on_stack(), this function has no effect for
	264	* !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
	265	*/
	266	void destroy_rcu_head_on_stack(struct rcu_head *head)
	267	{
	268	debug_object_free(head, &rcuhead_debug_descr);
	269	}
	270	EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
	271
	272	struct debug_obj_descr rcuhead_debug_descr = {
	273	.name = "rcu_head",
551d55a9	274	.fixup_activate = rcuhead_fixup_activate,
551d55a9 MD	275	};
	276	EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
	277	#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
91afaf30 PM	278
91afaf30 PM	279	#if defined(CONFIG_TREE_RCU) \|\| defined(CONFIG_TREE_PREEMPT_RCU) \|\| defined(CONFIG_RCU_TRACE)
e66c33d5	280	void do_trace_rcu_torture_read(const char rcutorturename, struct rcu_head rhp,
52494535 PM	281	unsigned long secs,
52494535 PM	282	unsigned long c_old, unsigned long c)
91afaf30	283	{
52494535	284	trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c);
91afaf30 PM	285	}
	286	EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
	287	#else
52494535 PM	288	#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
52494535 PM	289	do { } while (0)
91afaf30	290	#endif
6bfc09e2 PM	291
	292	#ifdef CONFIG_RCU_STALL_COMMON
	293
	294	#ifdef CONFIG_PROVE_RCU
	295	#define RCU_STALL_DELAY_DELTA (5 * HZ)
	296	#else
	297	#define RCU_STALL_DELAY_DELTA 0
	298	#endif
	299
	300	int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
	301	int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
	302
	303	module_param(rcu_cpu_stall_suppress, int, 0644);
	304	module_param(rcu_cpu_stall_timeout, int, 0644);
	305
	306	int rcu_jiffies_till_stall_check(void)
	307	{
	308	int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout);
	309
	310	/*
	311	* Limit check must be consistent with the Kconfig limits
	312	* for CONFIG_RCU_CPU_STALL_TIMEOUT.
	313	*/
	314	if (till_stall_check < 3) {
	315	ACCESS_ONCE(rcu_cpu_stall_timeout) = 3;
	316	till_stall_check = 3;
	317	} else if (till_stall_check > 300) {
	318	ACCESS_ONCE(rcu_cpu_stall_timeout) = 300;
	319	till_stall_check = 300;
	320	}
	321	return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
	322	}
	323
	324	static int rcu_panic(struct notifier_block this, unsigned long ev, void ptr)
	325	{
	326	rcu_cpu_stall_suppress = 1;
	327	return NOTIFY_DONE;
	328	}
	329
	330	static struct notifier_block rcu_panic_block = {
	331	.notifier_call = rcu_panic,
	332	};
	333
	334	static int __init check_cpu_stall_init(void)
	335	{
	336	atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
	337	return 0;
	338	}
	339	early_initcall(check_cpu_stall_init);
	340
	341	#endif /* #ifdef CONFIG_RCU_STALL_COMMON */