[GitHub/mt8127/android_kernel_alcatel_ttab.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>

#define CREATE_TRACE_POINTS
#include <trace/events/rcu.h>

#include "rcu.h"

#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);
#endif

#ifdef CONFIG_DEBUG_LOCK_ALLOC

int 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.
 */
int rcu_read_lock_bh_held(void)
{
	if (!debug_lockdep_rcu_enabled())
		return 1;
	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_init is called when:
 * - an active object is initialized
 */
static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
{
	struct rcu_head *head = addr;

	switch (state) {
	case ODEBUG_STATE_ACTIVE:
		/*
		 * Ensure that queued callbacks are all executed.
		 * If we detect that we are nested in a RCU read-side critical
		 * section, we should simply fail, otherwise we would deadlock.
		 * In !PREEMPT configurations, there is no way to tell if we are
		 * in a RCU read-side critical section or not, so we never
		 * attempt any fixup and just print a warning.
		 */
#ifndef CONFIG_PREEMPT
		WARN_ON_ONCE(1);
		return 0;
#endif
		if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
		    irqs_disabled()) {
			WARN_ON_ONCE(1);
			return 0;
		}
		rcu_barrier();
		rcu_barrier_sched();
		rcu_barrier_bh();
		debug_object_init(head, &rcuhead_debug_descr);
		return 1;
	default:
		return 0;
	}
}

/*
 * 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;

	case ODEBUG_STATE_ACTIVE:
		/*
		 * Ensure that queued callbacks are all executed.
		 * If we detect that we are nested in a RCU read-side critical
		 * section, we should simply fail, otherwise we would deadlock.
		 * In !PREEMPT configurations, there is no way to tell if we are
		 * in a RCU read-side critical section or not, so we never
		 * attempt any fixup and just print a warning.
		 */
#ifndef CONFIG_PREEMPT
		WARN_ON_ONCE(1);
		return 0;
#endif
		if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
		    irqs_disabled()) {
			WARN_ON_ONCE(1);
			return 0;
		}
		rcu_barrier();
		rcu_barrier_sched();
		rcu_barrier_bh();
		debug_object_activate(head, &rcuhead_debug_descr);
		return 1;
	default:
		return 0;
	}
}

/*
 * fixup_free is called when:
 * - an active object is freed
 */
static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
{
	struct rcu_head *head = addr;

	switch (state) {
	case ODEBUG_STATE_ACTIVE:
		/*
		 * Ensure that queued callbacks are all executed.
		 * If we detect that we are nested in a RCU read-side critical
		 * section, we should simply fail, otherwise we would deadlock.
		 * In !PREEMPT configurations, there is no way to tell if we are
		 * in a RCU read-side critical section or not, so we never
		 * attempt any fixup and just print a warning.
		 */
#ifndef CONFIG_PREEMPT
		WARN_ON_ONCE(1);
		return 0;
#endif
		if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
		    irqs_disabled()) {
			WARN_ON_ONCE(1);
			return 0;
		}
		rcu_barrier();
		rcu_barrier_sched();
		rcu_barrier_bh();
		debug_object_free(head, &rcuhead_debug_descr);
		return 1;
	default:
		return 0;
	}
}

/**
 * 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_init = rcuhead_fixup_init,
	.fixup_activate = rcuhead_fixup_activate,
	.fixup_free = rcuhead_fixup_free,
};
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(char *rcutorturename, struct rcu_head *rhp)
{
	trace_rcu_torture_read(rcutorturename, rhp);
}
EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
#else
#define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
#endif
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>
1da177e4	48
29c00b4a PM	49	#define CREATE_TRACE_POINTS
	50	#include <trace/events/rcu.h>
	51
	52	#include "rcu.h"
	53
162cc279 PM	54	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	55	static struct lock_class_key rcu_lock_key;
	56	struct lockdep_map rcu_lock_map =
	57	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
	58	EXPORT_SYMBOL_GPL(rcu_lock_map);
632ee200 PM	59
	60	static struct lock_class_key rcu_bh_lock_key;
	61	struct lockdep_map rcu_bh_lock_map =
	62	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
	63	EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
	64
	65	static struct lock_class_key rcu_sched_lock_key;
	66	struct lockdep_map rcu_sched_lock_map =
	67	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
	68	EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
162cc279 PM	69	#endif
162cc279 PM	70
e3818b8d PM	71	#ifdef CONFIG_DEBUG_LOCK_ALLOC
e3818b8d PM	72
bc293d62 PM	73	int debug_lockdep_rcu_enabled(void)
	74	{
	75	return rcu_scheduler_active && debug_locks &&
	76	current->lockdep_recursion == 0;
	77	}
	78	EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
	79
e3818b8d	80	/**
ca5ecddf	81	* rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
e3818b8d PM	82	*
	83	* Check for bottom half being disabled, which covers both the
	84	* CONFIG_PROVE_RCU and not cases. Note that if someone uses
	85	* rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
ca5ecddf PM	86	* will show the situation. This is useful for debug checks in functions
	87	* that require that they be called within an RCU read-side critical
	88	* section.
e3818b8d PM	89	*
	90	* Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
	91	*/
	92	int rcu_read_lock_bh_held(void)
	93	{
	94	if (!debug_lockdep_rcu_enabled())
	95	return 1;
773e3f93	96	return in_softirq() \|\| irqs_disabled();
e3818b8d PM	97	}
	98	EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
	99
	100	#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
	101
2c42818e PM	102	struct rcu_synchronize {
	103	struct rcu_head head;
	104	struct completion completion;
	105	};
	106
fbf6bfca PM	107	/*
	108	* Awaken the corresponding synchronize_rcu() instance now that a
	109	* grace period has elapsed.
	110	*/
2c42818e	111	static void wakeme_after_rcu(struct rcu_head *head)
21a1ea9e	112	{
01c1c660 PM	113	struct rcu_synchronize *rcu;
	114
	115	rcu = container_of(head, struct rcu_synchronize, head);
	116	complete(&rcu->completion);
21a1ea9e	117	}
ee84b824	118
2c42818e PM	119	void wait_rcu_gp(call_rcu_func_t crf)
	120	{
	121	struct rcu_synchronize rcu;
	122
	123	init_rcu_head_on_stack(&rcu.head);
	124	init_completion(&rcu.completion);
	125	/* Will wake me after RCU finished. */
	126	crf(&rcu.head, wakeme_after_rcu);
	127	/* Wait for it. */
	128	wait_for_completion(&rcu.completion);
	129	destroy_rcu_head_on_stack(&rcu.head);
	130	}
	131	EXPORT_SYMBOL_GPL(wait_rcu_gp);
	132
ee84b824 PM	133	#ifdef CONFIG_PROVE_RCU
	134	/*
	135	* wrapper function to avoid #include problems.
	136	*/
	137	int rcu_my_thread_group_empty(void)
	138	{
	139	return thread_group_empty(current);
	140	}
	141	EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
	142	#endif /* #ifdef CONFIG_PROVE_RCU */
551d55a9 MD	143
	144	#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
	145	static inline void debug_init_rcu_head(struct rcu_head *head)
	146	{
	147	debug_object_init(head, &rcuhead_debug_descr);
	148	}
	149
	150	static inline void debug_rcu_head_free(struct rcu_head *head)
	151	{
	152	debug_object_free(head, &rcuhead_debug_descr);
	153	}
	154
	155	/*
	156	* fixup_init is called when:
	157	* - an active object is initialized
	158	*/
	159	static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
	160	{
	161	struct rcu_head *head = addr;
	162
	163	switch (state) {
	164	case ODEBUG_STATE_ACTIVE:
	165	/*
	166	* Ensure that queued callbacks are all executed.
	167	* If we detect that we are nested in a RCU read-side critical
	168	* section, we should simply fail, otherwise we would deadlock.
fc2ecf7e MD	169	* In !PREEMPT configurations, there is no way to tell if we are
	170	* in a RCU read-side critical section or not, so we never
	171	* attempt any fixup and just print a warning.
551d55a9	172	*/
fc2ecf7e	173	#ifndef CONFIG_PREEMPT
108aae22	174	WARN_ON_ONCE(1);
fc2ecf7e MD	175	return 0;
fc2ecf7e MD	176	#endif
551d55a9 MD	177	if (rcu_preempt_depth() != 0 \|\| preempt_count() != 0 \|\|
551d55a9 MD	178	irqs_disabled()) {
108aae22	179	WARN_ON_ONCE(1);
551d55a9 MD	180	return 0;
	181	}
	182	rcu_barrier();
	183	rcu_barrier_sched();
	184	rcu_barrier_bh();
	185	debug_object_init(head, &rcuhead_debug_descr);
	186	return 1;
	187	default:
	188	return 0;
	189	}
	190	}
	191
	192	/*
	193	* fixup_activate is called when:
	194	* - an active object is activated
	195	* - an unknown object is activated (might be a statically initialized object)
	196	* Activation is performed internally by call_rcu().
	197	*/
	198	static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
	199	{
	200	struct rcu_head *head = addr;
	201
	202	switch (state) {
	203
	204	case ODEBUG_STATE_NOTAVAILABLE:
	205	/*
	206	* This is not really a fixup. We just make sure that it is
	207	* tracked in the object tracker.
	208	*/
	209	debug_object_init(head, &rcuhead_debug_descr);
	210	debug_object_activate(head, &rcuhead_debug_descr);
	211	return 0;
	212
	213	case ODEBUG_STATE_ACTIVE:
	214	/*
	215	* Ensure that queued callbacks are all executed.
	216	* If we detect that we are nested in a RCU read-side critical
	217	* section, we should simply fail, otherwise we would deadlock.
fc2ecf7e MD	218	* In !PREEMPT configurations, there is no way to tell if we are
	219	* in a RCU read-side critical section or not, so we never
	220	* attempt any fixup and just print a warning.
551d55a9	221	*/
fc2ecf7e	222	#ifndef CONFIG_PREEMPT
108aae22	223	WARN_ON_ONCE(1);
fc2ecf7e MD	224	return 0;
fc2ecf7e MD	225	#endif
551d55a9 MD	226	if (rcu_preempt_depth() != 0 \|\| preempt_count() != 0 \|\|
551d55a9 MD	227	irqs_disabled()) {
108aae22	228	WARN_ON_ONCE(1);
551d55a9 MD	229	return 0;
	230	}
	231	rcu_barrier();
	232	rcu_barrier_sched();
	233	rcu_barrier_bh();
	234	debug_object_activate(head, &rcuhead_debug_descr);
	235	return 1;
	236	default:
	237	return 0;
	238	}
	239	}
	240
	241	/*
	242	* fixup_free is called when:
	243	* - an active object is freed
	244	*/
	245	static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
	246	{
	247	struct rcu_head *head = addr;
	248
	249	switch (state) {
	250	case ODEBUG_STATE_ACTIVE:
	251	/*
	252	* Ensure that queued callbacks are all executed.
	253	* If we detect that we are nested in a RCU read-side critical
	254	* section, we should simply fail, otherwise we would deadlock.
fc2ecf7e MD	255	* In !PREEMPT configurations, there is no way to tell if we are
	256	* in a RCU read-side critical section or not, so we never
	257	* attempt any fixup and just print a warning.
551d55a9	258	*/
fc2ecf7e	259	#ifndef CONFIG_PREEMPT
108aae22	260	WARN_ON_ONCE(1);
fc2ecf7e MD	261	return 0;
fc2ecf7e MD	262	#endif
551d55a9 MD	263	if (rcu_preempt_depth() != 0 \|\| preempt_count() != 0 \|\|
551d55a9 MD	264	irqs_disabled()) {
108aae22	265	WARN_ON_ONCE(1);
551d55a9 MD	266	return 0;
	267	}
	268	rcu_barrier();
	269	rcu_barrier_sched();
	270	rcu_barrier_bh();
	271	debug_object_free(head, &rcuhead_debug_descr);
	272	return 1;
551d55a9 MD	273	default:
	274	return 0;
	275	}
	276	}
	277
	278	/**
	279	* init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
	280	* @head: pointer to rcu_head structure to be initialized
	281	*
	282	* This function informs debugobjects of a new rcu_head structure that
	283	* has been allocated as an auto variable on the stack. This function
	284	* is not required for rcu_head structures that are statically defined or
	285	* that are dynamically allocated on the heap. This function has no
	286	* effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
	287	*/
	288	void init_rcu_head_on_stack(struct rcu_head *head)
	289	{
	290	debug_object_init_on_stack(head, &rcuhead_debug_descr);
	291	}
	292	EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
	293
	294	/**
	295	* destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
	296	* @head: pointer to rcu_head structure to be initialized
	297	*
	298	* This function informs debugobjects that an on-stack rcu_head structure
	299	* is about to go out of scope. As with init_rcu_head_on_stack(), this
	300	* function is not required for rcu_head structures that are statically
	301	* defined or that are dynamically allocated on the heap. Also as with
	302	* init_rcu_head_on_stack(), this function has no effect for
	303	* !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
	304	*/
	305	void destroy_rcu_head_on_stack(struct rcu_head *head)
	306	{
	307	debug_object_free(head, &rcuhead_debug_descr);
	308	}
	309	EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
	310
	311	struct debug_obj_descr rcuhead_debug_descr = {
	312	.name = "rcu_head",
	313	.fixup_init = rcuhead_fixup_init,
	314	.fixup_activate = rcuhead_fixup_activate,
	315	.fixup_free = rcuhead_fixup_free,
	316	};
	317	EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
	318	#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
91afaf30 PM	319
	320	#if defined(CONFIG_TREE_RCU) \|\| defined(CONFIG_TREE_PREEMPT_RCU) \|\| defined(CONFIG_RCU_TRACE)
	321	void do_trace_rcu_torture_read(char rcutorturename, struct rcu_head rhp)
	322	{
	323	trace_rcu_torture_read(rcutorturename, rhp);
	324	}
	325	EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
	326	#else
	327	#define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
	328	#endif