[deliverable/linux.git] / kernel / rcu / update.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, 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;
		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
void init_rcu_head(struct rcu_head *head)
{
	debug_object_init(head, &rcuhead_debug_descr);
}

void destroy_rcu_head(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;
}

void rcu_sysrq_start(void)
{
	if (!rcu_cpu_stall_suppress)
		rcu_cpu_stall_suppress = 2;
}

void rcu_sysrq_end(void)
{
	if (rcu_cpu_stall_suppress == 2)
		rcu_cpu_stall_suppress = 0;
}

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
87de1cfd PM	15	* along with this program; if not, you can access it online at
87de1cfd PM	16	* http://www.gnu.org/licenses/gpl-2.0.html.
1da177e4	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	51	#define CREATE_TRACE_POINTS
29c00b4a PM	52
	53	#include "rcu.h"
	54
4102adab PM	55	MODULE_ALIAS("rcupdate");
	56	#ifdef MODULE_PARAM_PREFIX
	57	#undef MODULE_PARAM_PREFIX
	58	#endif
	59	#define MODULE_PARAM_PREFIX "rcupdate."
	60
3705b88d AM	61	module_param(rcu_expedited, int, 0);
3705b88d AM	62
9dd8fb16 PM	63	#ifdef CONFIG_PREEMPT_RCU
9dd8fb16 PM	64
2a3fa843 PM	65	/*
	66	* Preemptible RCU implementation for rcu_read_lock().
	67	* Just increment ->rcu_read_lock_nesting, shared state will be updated
	68	* if we block.
	69	*/
	70	void __rcu_read_lock(void)
	71	{
	72	current->rcu_read_lock_nesting++;
	73	barrier(); /* critical section after entry code. */
	74	}
	75	EXPORT_SYMBOL_GPL(__rcu_read_lock);
	76
	77	/*
	78	* Preemptible RCU implementation for rcu_read_unlock().
	79	* Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
	80	* rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
	81	* invoke rcu_read_unlock_special() to clean up after a context switch
	82	* in an RCU read-side critical section and other special cases.
	83	*/
	84	void __rcu_read_unlock(void)
	85	{
	86	struct task_struct *t = current;
	87
	88	if (t->rcu_read_lock_nesting != 1) {
	89	--t->rcu_read_lock_nesting;
	90	} else {
	91	barrier(); /* critical section before exit code. */
	92	t->rcu_read_lock_nesting = INT_MIN;
	93	barrier(); /* assign before ->rcu_read_unlock_special load */
	94	if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
	95	rcu_read_unlock_special(t);
	96	barrier(); /* ->rcu_read_unlock_special load before assign */
	97	t->rcu_read_lock_nesting = 0;
	98	}
	99	#ifdef CONFIG_PROVE_LOCKING
	100	{
	101	int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
	102
	103	WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
	104	}
	105	#endif /* #ifdef CONFIG_PROVE_LOCKING */
	106	}
	107	EXPORT_SYMBOL_GPL(__rcu_read_unlock);
	108
2439b696	109	#endif /* #ifdef CONFIG_PREEMPT_RCU */
9dd8fb16	110
162cc279 PM	111	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	112	static struct lock_class_key rcu_lock_key;
	113	struct lockdep_map rcu_lock_map =
	114	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
	115	EXPORT_SYMBOL_GPL(rcu_lock_map);
632ee200 PM	116
	117	static struct lock_class_key rcu_bh_lock_key;
	118	struct lockdep_map rcu_bh_lock_map =
	119	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
	120	EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
	121
	122	static struct lock_class_key rcu_sched_lock_key;
	123	struct lockdep_map rcu_sched_lock_map =
	124	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
	125	EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
e3818b8d	126
24ef659a PM	127	static struct lock_class_key rcu_callback_key;
	128	struct lockdep_map rcu_callback_map =
	129	STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key);
	130	EXPORT_SYMBOL_GPL(rcu_callback_map);
	131
a0a5a056	132	int notrace debug_lockdep_rcu_enabled(void)
bc293d62 PM	133	{
	134	return rcu_scheduler_active && debug_locks &&
	135	current->lockdep_recursion == 0;
	136	}
	137	EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
	138
e3818b8d	139	/**
ca5ecddf	140	* rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
e3818b8d PM	141	*
	142	* Check for bottom half being disabled, which covers both the
	143	* CONFIG_PROVE_RCU and not cases. Note that if someone uses
	144	* rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
ca5ecddf PM	145	* will show the situation. This is useful for debug checks in functions
	146	* that require that they be called within an RCU read-side critical
	147	* section.
e3818b8d PM	148	*
e3818b8d PM	149	* Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
c0d6d01b PM	150	*
	151	* Note that rcu_read_lock() is disallowed if the CPU is either idle or
	152	* offline from an RCU perspective, so check for those as well.
e3818b8d PM	153	*/
	154	int rcu_read_lock_bh_held(void)
	155	{
	156	if (!debug_lockdep_rcu_enabled())
	157	return 1;
5c173eb8	158	if (!rcu_is_watching())
e6b80a3b	159	return 0;
c0d6d01b PM	160	if (!rcu_lockdep_current_cpu_online())
c0d6d01b PM	161	return 0;
773e3f93	162	return in_softirq() \|\| irqs_disabled();
e3818b8d PM	163	}
	164	EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
	165
	166	#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
	167
2c42818e PM	168	struct rcu_synchronize {
	169	struct rcu_head head;
	170	struct completion completion;
	171	};
	172
fbf6bfca PM	173	/*
	174	* Awaken the corresponding synchronize_rcu() instance now that a
	175	* grace period has elapsed.
	176	*/
2c42818e	177	static void wakeme_after_rcu(struct rcu_head *head)
21a1ea9e	178	{
01c1c660 PM	179	struct rcu_synchronize *rcu;
	180
	181	rcu = container_of(head, struct rcu_synchronize, head);
	182	complete(&rcu->completion);
21a1ea9e	183	}
ee84b824	184
2c42818e PM	185	void wait_rcu_gp(call_rcu_func_t crf)
	186	{
	187	struct rcu_synchronize rcu;
	188
	189	init_rcu_head_on_stack(&rcu.head);
	190	init_completion(&rcu.completion);
	191	/* Will wake me after RCU finished. */
	192	crf(&rcu.head, wakeme_after_rcu);
	193	/* Wait for it. */
	194	wait_for_completion(&rcu.completion);
	195	destroy_rcu_head_on_stack(&rcu.head);
	196	}
	197	EXPORT_SYMBOL_GPL(wait_rcu_gp);
	198
551d55a9	199	#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
546a9d85	200	void init_rcu_head(struct rcu_head *head)
551d55a9 MD	201	{
	202	debug_object_init(head, &rcuhead_debug_descr);
	203	}
	204
546a9d85	205	void destroy_rcu_head(struct rcu_head *head)
551d55a9 MD	206	{
	207	debug_object_free(head, &rcuhead_debug_descr);
	208	}
	209
551d55a9 MD	210	/*
	211	* fixup_activate is called when:
	212	* - an active object is activated
	213	* - an unknown object is activated (might be a statically initialized object)
	214	* Activation is performed internally by call_rcu().
	215	*/
	216	static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
	217	{
	218	struct rcu_head *head = addr;
	219
	220	switch (state) {
	221
	222	case ODEBUG_STATE_NOTAVAILABLE:
	223	/*
	224	* This is not really a fixup. We just make sure that it is
	225	* tracked in the object tracker.
	226	*/
	227	debug_object_init(head, &rcuhead_debug_descr);
	228	debug_object_activate(head, &rcuhead_debug_descr);
	229	return 0;
551d55a9	230	default:
551d55a9	231	return 1;
551d55a9 MD	232	}
	233	}
	234
	235	/**
	236	* init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
	237	* @head: pointer to rcu_head structure to be initialized
	238	*
	239	* This function informs debugobjects of a new rcu_head structure that
	240	* has been allocated as an auto variable on the stack. This function
	241	* is not required for rcu_head structures that are statically defined or
	242	* that are dynamically allocated on the heap. This function has no
	243	* effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
	244	*/
	245	void init_rcu_head_on_stack(struct rcu_head *head)
	246	{
	247	debug_object_init_on_stack(head, &rcuhead_debug_descr);
	248	}
	249	EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
	250
	251	/**
	252	* destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
	253	* @head: pointer to rcu_head structure to be initialized
	254	*
	255	* This function informs debugobjects that an on-stack rcu_head structure
	256	* is about to go out of scope. As with init_rcu_head_on_stack(), this
	257	* function is not required for rcu_head structures that are statically
	258	* defined or that are dynamically allocated on the heap. Also as with
	259	* init_rcu_head_on_stack(), this function has no effect for
	260	* !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
	261	*/
	262	void destroy_rcu_head_on_stack(struct rcu_head *head)
	263	{
	264	debug_object_free(head, &rcuhead_debug_descr);
	265	}
	266	EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
	267
	268	struct debug_obj_descr rcuhead_debug_descr = {
	269	.name = "rcu_head",
551d55a9	270	.fixup_activate = rcuhead_fixup_activate,
551d55a9 MD	271	};
	272	EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
	273	#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
91afaf30 PM	274
91afaf30 PM	275	#if defined(CONFIG_TREE_RCU) \|\| defined(CONFIG_TREE_PREEMPT_RCU) \|\| defined(CONFIG_RCU_TRACE)
e66c33d5	276	void do_trace_rcu_torture_read(const char rcutorturename, struct rcu_head rhp,
52494535 PM	277	unsigned long secs,
52494535 PM	278	unsigned long c_old, unsigned long c)
91afaf30	279	{
52494535	280	trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c);
91afaf30 PM	281	}
	282	EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
	283	#else
52494535 PM	284	#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
52494535 PM	285	do { } while (0)
91afaf30	286	#endif
6bfc09e2 PM	287
	288	#ifdef CONFIG_RCU_STALL_COMMON
	289
	290	#ifdef CONFIG_PROVE_RCU
	291	#define RCU_STALL_DELAY_DELTA (5 * HZ)
	292	#else
	293	#define RCU_STALL_DELAY_DELTA 0
	294	#endif
	295
	296	int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
01896f7e	297	static int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
6bfc09e2 PM	298
	299	module_param(rcu_cpu_stall_suppress, int, 0644);
	300	module_param(rcu_cpu_stall_timeout, int, 0644);
	301
	302	int rcu_jiffies_till_stall_check(void)
	303	{
	304	int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout);
	305
	306	/*
	307	* Limit check must be consistent with the Kconfig limits
	308	* for CONFIG_RCU_CPU_STALL_TIMEOUT.
	309	*/
	310	if (till_stall_check < 3) {
	311	ACCESS_ONCE(rcu_cpu_stall_timeout) = 3;
	312	till_stall_check = 3;
	313	} else if (till_stall_check > 300) {
	314	ACCESS_ONCE(rcu_cpu_stall_timeout) = 300;
	315	till_stall_check = 300;
	316	}
	317	return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
	318	}
	319
61f38db3 RR	320	void rcu_sysrq_start(void)
	321	{
	322	if (!rcu_cpu_stall_suppress)
	323	rcu_cpu_stall_suppress = 2;
	324	}
	325
	326	void rcu_sysrq_end(void)
	327	{
	328	if (rcu_cpu_stall_suppress == 2)
	329	rcu_cpu_stall_suppress = 0;
	330	}
	331
6bfc09e2 PM	332	static int rcu_panic(struct notifier_block this, unsigned long ev, void ptr)
	333	{
	334	rcu_cpu_stall_suppress = 1;
	335	return NOTIFY_DONE;
	336	}
	337
	338	static struct notifier_block rcu_panic_block = {
	339	.notifier_call = rcu_panic,
	340	};
	341
	342	static int __init check_cpu_stall_init(void)
	343	{
	344	atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
	345	return 0;
	346	}
	347	early_initcall(check_cpu_stall_init);
	348
	349	#endif /* #ifdef CONFIG_RCU_STALL_COMMON */