[userspace-rcu.git] / urcu-qsbr.c

/*
 * urcu-qsbr.c
 *
 * Userspace RCU QSBR library
 *
 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 *
 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
 */

#define _GNU_SOURCE
#define _LGPL_SOURCE
#include <stdio.h>
#include <pthread.h>
#include <signal.h>
#include <assert.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <errno.h>
#include <poll.h>

#include "urcu/wfcqueue.h"
#include "urcu/map/urcu-qsbr.h"
#define BUILD_QSBR_LIB
#include "urcu/static/urcu-qsbr.h"
#include "urcu-pointer.h"
#include "urcu/tls-compat.h"

#include "urcu-die.h"
#include "urcu-wait.h"

/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
#undef _LGPL_SOURCE
#include "urcu-qsbr.h"
#define _LGPL_SOURCE

void __attribute__((destructor)) rcu_exit(void);

/*
 * rcu_gp_lock ensures mutual exclusion between threads calling
 * synchronize_rcu().
 */
static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
/*
 * rcu_registry_lock ensures mutual exclusion between threads
 * registering and unregistering themselves to/from the registry, and
 * with threads reading that registry from synchronize_rcu(). However,
 * this lock is not held all the way through the completion of awaiting
 * for the grace period. It is sporadically released between iterations
 * on the registry.
 * rcu_registry_lock may nest inside rcu_gp_lock.
 */
static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER;
struct rcu_gp rcu_gp = { .ctr = RCU_GP_ONLINE };

/*
 * Active attempts to check for reader Q.S. before calling futex().
 */
#define RCU_QS_ACTIVE_ATTEMPTS 100

/*
 * Written to only by each individual reader. Read by both the reader and the
 * writers.
 */
__DEFINE_URCU_TLS_GLOBAL(struct rcu_reader, rcu_reader);

#ifdef DEBUG_YIELD
unsigned int rcu_yield_active;
__DEFINE_URCU_TLS_GLOBAL(unsigned int, rcu_rand_yield);
#endif

static CDS_LIST_HEAD(registry);

/*
 * Queue keeping threads awaiting to wait for a grace period. Contains
 * struct gp_waiters_thread objects.
 */
static DEFINE_URCU_WAIT_QUEUE(gp_waiters);

static void mutex_lock(pthread_mutex_t *mutex)
{
	int ret;

#ifndef DISTRUST_SIGNALS_EXTREME
	ret = pthread_mutex_lock(mutex);
	if (ret)
		urcu_die(ret);
#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	while ((ret = pthread_mutex_trylock(mutex)) != 0) {
		if (ret != EBUSY && ret != EINTR)
			urcu_die(ret);
		poll(NULL,0,10);
	}
#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
}

static void mutex_unlock(pthread_mutex_t *mutex)
{
	int ret;

	ret = pthread_mutex_unlock(mutex);
	if (ret)
		urcu_die(ret);
}

/*
 * synchronize_rcu() waiting. Single thread.
 */
static void wait_gp(void)
{
	/* Read reader_gp before read futex */
	cmm_smp_rmb();
	if (uatomic_read(&rcu_gp.futex) == -1)
		futex_noasync(&rcu_gp.futex, FUTEX_WAIT, -1,
		      NULL, NULL, 0);
}

/*
 * Always called with rcu_registry lock held. Releases this lock between
 * iterations and grabs it again. Holds the lock when it returns.
 */
static void wait_for_readers(struct cds_list_head *input_readers,
			struct cds_list_head *cur_snap_readers,
			struct cds_list_head *qsreaders)
{
	unsigned int wait_loops = 0;
	struct rcu_reader *index, *tmp;

	/*
	 * Wait for each thread URCU_TLS(rcu_reader).ctr to either
	 * indicate quiescence (offline), or for them to observe the
	 * current rcu_gp.ctr value.
	 */
	for (;;) {
		if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
			wait_loops++;
		if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
			uatomic_set(&rcu_gp.futex, -1);
			/*
			 * Write futex before write waiting (the other side
			 * reads them in the opposite order).
			 */
			cmm_smp_wmb();
			cds_list_for_each_entry(index, input_readers, node) {
				_CMM_STORE_SHARED(index->waiting, 1);
			}
			/* Write futex before read reader_gp */
			cmm_smp_mb();
		}
		cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
			switch (rcu_reader_state(&index->ctr)) {
			case RCU_READER_ACTIVE_CURRENT:
				if (cur_snap_readers) {
					cds_list_move(&index->node,
						cur_snap_readers);
					break;
				}
				/* Fall-through */
			case RCU_READER_INACTIVE:
				cds_list_move(&index->node, qsreaders);
				break;
			case RCU_READER_ACTIVE_OLD:
				/*
				 * Old snapshot. Leaving node in
				 * input_readers will make us busy-loop
				 * until the snapshot becomes current or
				 * the reader becomes inactive.
				 */
				break;
			}
		}

		if (cds_list_empty(input_readers)) {
			if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
				/* Read reader_gp before write futex */
				cmm_smp_mb();
				uatomic_set(&rcu_gp.futex, 0);
			}
			break;
		} else {
			/* Temporarily unlock the registry lock. */
			mutex_unlock(&rcu_registry_lock);
			if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
				wait_gp();
			} else {
#ifndef HAS_INCOHERENT_CACHES
				caa_cpu_relax();
#else /* #ifndef HAS_INCOHERENT_CACHES */
				cmm_smp_mb();
#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
			}
			/* Re-lock the registry lock before the next loop. */
			mutex_lock(&rcu_registry_lock);
		}
	}
}

/*
 * Using a two-subphases algorithm for architectures with smaller than 64-bit
 * long-size to ensure we do not encounter an overflow bug.
 */

#if (CAA_BITS_PER_LONG < 64)
void synchronize_rcu(void)
{
	CDS_LIST_HEAD(cur_snap_readers);
	CDS_LIST_HEAD(qsreaders);
	unsigned long was_online;
	DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
	struct urcu_waiters waiters;

	was_online = rcu_read_ongoing();

	/* All threads should read qparity before accessing data structure
	 * where new ptr points to.  In the "then" case, rcu_thread_offline
	 * includes a memory barrier.
	 *
	 * Mark the writer thread offline to make sure we don't wait for
	 * our own quiescent state. This allows using synchronize_rcu()
	 * in threads registered as readers.
	 */
	if (was_online)
		rcu_thread_offline();
	else
		cmm_smp_mb();

	/*
	 * Add ourself to gp_waiters queue of threads awaiting to wait
	 * for a grace period. Proceed to perform the grace period only
	 * if we are the first thread added into the queue.
	 */
	if (urcu_wait_add(&gp_waiters, &wait) != 0) {
		/* Not first in queue: will be awakened by another thread. */
		urcu_adaptative_busy_wait(&wait);
		goto gp_end;
	}
	/* We won't need to wake ourself up */
	urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);

	mutex_lock(&rcu_gp_lock);

	/*
	 * Move all waiters into our local queue.
	 */
	urcu_move_waiters(&waiters, &gp_waiters);

	mutex_lock(&rcu_registry_lock);

	if (cds_list_empty(&registry))
		goto out;

	/*
	 * Wait for readers to observe original parity or be quiescent.
	 * wait_for_readers() can release and grab again rcu_registry_lock
	 * interally.
	 */
	wait_for_readers(&registry, &cur_snap_readers, &qsreaders);

	/*
	 * Must finish waiting for quiescent state for original parity
	 * before committing next rcu_gp.ctr update to memory. Failure
	 * to do so could result in the writer waiting forever while new
	 * readers are always accessing data (no progress).  Enforce
	 * compiler-order of load URCU_TLS(rcu_reader).ctr before store
	 * to rcu_gp.ctr.
	 */
	cmm_barrier();

	/*
	 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	 * model easier to understand. It does not have a big performance impact
	 * anyway, given this is the write-side.
	 */
	cmm_smp_mb();

	/* Switch parity: 0 -> 1, 1 -> 0 */
	CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR);

	/*
	 * Must commit rcu_gp.ctr update to memory before waiting for
	 * quiescent state. Failure to do so could result in the writer
	 * waiting forever while new readers are always accessing data
	 * (no progress). Enforce compiler-order of store to rcu_gp.ctr
	 * before load URCU_TLS(rcu_reader).ctr.
	 */
	cmm_barrier();

	/*
	 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	 * model easier to understand. It does not have a big performance impact
	 * anyway, given this is the write-side.
	 */
	cmm_smp_mb();

	/*
	 * Wait for readers to observe new parity or be quiescent.
	 * wait_for_readers() can release and grab again rcu_registry_lock
	 * interally.
	 */
	wait_for_readers(&cur_snap_readers, NULL, &qsreaders);

	/*
	 * Put quiescent reader list back into registry.
	 */
	cds_list_splice(&qsreaders, &registry);
out:
	mutex_unlock(&rcu_registry_lock);
	mutex_unlock(&rcu_gp_lock);
	urcu_wake_all_waiters(&waiters);
gp_end:
	/*
	 * Finish waiting for reader threads before letting the old ptr being
	 * freed.
	 */
	if (was_online)
		rcu_thread_online();
	else
		cmm_smp_mb();
}
#else /* !(CAA_BITS_PER_LONG < 64) */
void synchronize_rcu(void)
{
	CDS_LIST_HEAD(qsreaders);
	unsigned long was_online;
	DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
	struct urcu_waiters waiters;

	was_online = rcu_read_ongoing();

	/*
	 * Mark the writer thread offline to make sure we don't wait for
	 * our own quiescent state. This allows using synchronize_rcu()
	 * in threads registered as readers.
	 */
	if (was_online)
		rcu_thread_offline();
	else
		cmm_smp_mb();

	/*
	 * Add ourself to gp_waiters queue of threads awaiting to wait
	 * for a grace period. Proceed to perform the grace period only
	 * if we are the first thread added into the queue.
	 */
	if (urcu_wait_add(&gp_waiters, &wait) != 0) {
		/* Not first in queue: will be awakened by another thread. */
		urcu_adaptative_busy_wait(&wait);
		goto gp_end;
	}
	/* We won't need to wake ourself up */
	urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);

	mutex_lock(&rcu_gp_lock);

	/*
	 * Move all waiters into our local queue.
	 */
	urcu_move_waiters(&waiters, &gp_waiters);

	mutex_lock(&rcu_registry_lock);

	if (cds_list_empty(&registry))
		goto out;

	/* Increment current G.P. */
	CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr + RCU_GP_CTR);

	/*
	 * Must commit rcu_gp.ctr update to memory before waiting for
	 * quiescent state. Failure to do so could result in the writer
	 * waiting forever while new readers are always accessing data
	 * (no progress). Enforce compiler-order of store to rcu_gp.ctr
	 * before load URCU_TLS(rcu_reader).ctr.
	 */
	cmm_barrier();

	/*
	 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	 * model easier to understand. It does not have a big performance impact
	 * anyway, given this is the write-side.
	 */
	cmm_smp_mb();

	/*
	 * Wait for readers to observe new count of be quiescent.
	 * wait_for_readers() can release and grab again rcu_registry_lock
	 * interally.
	 */
	wait_for_readers(&registry, NULL, &qsreaders);

	/*
	 * Put quiescent reader list back into registry.
	 */
	cds_list_splice(&qsreaders, &registry);
out:
	mutex_unlock(&rcu_registry_lock);
	mutex_unlock(&rcu_gp_lock);
	urcu_wake_all_waiters(&waiters);
gp_end:
	if (was_online)
		rcu_thread_online();
	else
		cmm_smp_mb();
}
#endif  /* !(CAA_BITS_PER_LONG < 64) */

/*
 * library wrappers to be used by non-LGPL compatible source code.
 */

void rcu_read_lock(void)
{
	_rcu_read_lock();
}

void rcu_read_unlock(void)
{
	_rcu_read_unlock();
}

int rcu_read_ongoing(void)
{
	return _rcu_read_ongoing();
}

void rcu_quiescent_state(void)
{
	_rcu_quiescent_state();
}

void rcu_thread_offline(void)
{
	_rcu_thread_offline();
}

void rcu_thread_online(void)
{
	_rcu_thread_online();
}

void rcu_register_thread(void)
{
	URCU_TLS(rcu_reader).tid = pthread_self();
	assert(URCU_TLS(rcu_reader).ctr == 0);

	mutex_lock(&rcu_registry_lock);
	cds_list_add(&URCU_TLS(rcu_reader).node, &registry);
	mutex_unlock(&rcu_registry_lock);
	_rcu_thread_online();
}

void rcu_unregister_thread(void)
{
	/*
	 * We have to make the thread offline otherwise we end up dealocking
	 * with a waiting writer.
	 */
	_rcu_thread_offline();
	mutex_lock(&rcu_registry_lock);
	cds_list_del(&URCU_TLS(rcu_reader).node);
	mutex_unlock(&rcu_registry_lock);
}

void rcu_exit(void)
{
	/*
	 * Assertion disabled because call_rcu threads are now rcu
	 * readers, and left running at exit.
	 * assert(cds_list_empty(&registry));
	 */
}

DEFINE_RCU_FLAVOR(rcu_flavor);

#include "urcu-call-rcu-impl.h"
#include "urcu-defer-impl.h"
Commit	Line	Data
	1	/*
	2	* urcu-qsbr.c
	3	*
	4	* Userspace RCU QSBR library
	5	*
	6	* Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
	7	* Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
	8	*
	9	* This library is free software; you can redistribute it and/or
	10	* modify it under the terms of the GNU Lesser General Public
	11	* License as published by the Free Software Foundation; either
	12	* version 2.1 of the License, or (at your option) any later version.
	13	*
	14	* This library is distributed in the hope that it will be useful,
	15	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	16	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	17	* Lesser General Public License for more details.
	18	*
	19	* You should have received a copy of the GNU Lesser General Public
	20	* License along with this library; if not, write to the Free Software
	21	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
	22	*
	23	* IBM's contributions to this file may be relicensed under LGPLv2 or later.
	24	*/
	25
	26	#define _GNU_SOURCE
	27	#define _LGPL_SOURCE
	28	#include <stdio.h>
	29	#include <pthread.h>
	30	#include <signal.h>
	31	#include <assert.h>
	32	#include <stdlib.h>
	33	#include <stdint.h>
	34	#include <string.h>
	35	#include <errno.h>
	36	#include <poll.h>
	37
	38	#include "urcu/wfcqueue.h"
	39	#include "urcu/map/urcu-qsbr.h"
	40	#define BUILD_QSBR_LIB
	41	#include "urcu/static/urcu-qsbr.h"
	42	#include "urcu-pointer.h"
	43	#include "urcu/tls-compat.h"
	44
	45	#include "urcu-die.h"
	46	#include "urcu-wait.h"
	47
	48	/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
	49	#undef _LGPL_SOURCE
	50	#include "urcu-qsbr.h"
	51	#define _LGPL_SOURCE
	52
	53	void __attribute__((destructor)) rcu_exit(void);
	54
	55	/*
	56	* rcu_gp_lock ensures mutual exclusion between threads calling
	57	* synchronize_rcu().
	58	*/
	59	static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
	60	/*
	61	* rcu_registry_lock ensures mutual exclusion between threads
	62	* registering and unregistering themselves to/from the registry, and
	63	* with threads reading that registry from synchronize_rcu(). However,
	64	* this lock is not held all the way through the completion of awaiting
	65	* for the grace period. It is sporadically released between iterations
	66	* on the registry.
	67	* rcu_registry_lock may nest inside rcu_gp_lock.
	68	*/
	69	static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER;
	70	struct rcu_gp rcu_gp = { .ctr = RCU_GP_ONLINE };
	71
	72	/*
	73	* Active attempts to check for reader Q.S. before calling futex().
	74	*/
	75	#define RCU_QS_ACTIVE_ATTEMPTS 100
	76
	77	/*
	78	* Written to only by each individual reader. Read by both the reader and the
	79	* writers.
	80	*/
	81	__DEFINE_URCU_TLS_GLOBAL(struct rcu_reader, rcu_reader);
	82
	83	#ifdef DEBUG_YIELD
	84	unsigned int rcu_yield_active;
	85	__DEFINE_URCU_TLS_GLOBAL(unsigned int, rcu_rand_yield);
	86	#endif
	87
	88	static CDS_LIST_HEAD(registry);
	89
	90	/*
	91	* Queue keeping threads awaiting to wait for a grace period. Contains
	92	* struct gp_waiters_thread objects.
	93	*/
	94	static DEFINE_URCU_WAIT_QUEUE(gp_waiters);
	95
	96	static void mutex_lock(pthread_mutex_t *mutex)
	97	{
	98	int ret;
	99
	100	#ifndef DISTRUST_SIGNALS_EXTREME
	101	ret = pthread_mutex_lock(mutex);
	102	if (ret)
	103	urcu_die(ret);
	104	#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	105	while ((ret = pthread_mutex_trylock(mutex)) != 0) {
	106	if (ret != EBUSY && ret != EINTR)
	107	urcu_die(ret);
	108	poll(NULL,0,10);
	109	}
	110	#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
	111	}
	112
	113	static void mutex_unlock(pthread_mutex_t *mutex)
	114	{
	115	int ret;
	116
	117	ret = pthread_mutex_unlock(mutex);
	118	if (ret)
	119	urcu_die(ret);
	120	}
	121
	122	/*
	123	* synchronize_rcu() waiting. Single thread.
	124	*/
	125	static void wait_gp(void)
	126	{
	127	/* Read reader_gp before read futex */
	128	cmm_smp_rmb();
	129	if (uatomic_read(&rcu_gp.futex) == -1)
	130	futex_noasync(&rcu_gp.futex, FUTEX_WAIT, -1,
	131	NULL, NULL, 0);
	132	}
	133
	134	/*
	135	* Always called with rcu_registry lock held. Releases this lock between
	136	* iterations and grabs it again. Holds the lock when it returns.
	137	*/
	138	static void wait_for_readers(struct cds_list_head *input_readers,
	139	struct cds_list_head *cur_snap_readers,
	140	struct cds_list_head *qsreaders)
	141	{
	142	unsigned int wait_loops = 0;
	143	struct rcu_reader index, tmp;
	144
	145	/*
	146	* Wait for each thread URCU_TLS(rcu_reader).ctr to either
	147	* indicate quiescence (offline), or for them to observe the
	148	* current rcu_gp.ctr value.
	149	*/
	150	for (;;) {
	151	if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
	152	wait_loops++;
	153	if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
	154	uatomic_set(&rcu_gp.futex, -1);
	155	/*
	156	* Write futex before write waiting (the other side
	157	* reads them in the opposite order).
	158	*/
	159	cmm_smp_wmb();
	160	cds_list_for_each_entry(index, input_readers, node) {
	161	_CMM_STORE_SHARED(index->waiting, 1);
	162	}
	163	/* Write futex before read reader_gp */
	164	cmm_smp_mb();
	165	}
	166	cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
	167	switch (rcu_reader_state(&index->ctr)) {
	168	case RCU_READER_ACTIVE_CURRENT:
	169	if (cur_snap_readers) {
	170	cds_list_move(&index->node,
	171	cur_snap_readers);
	172	break;
	173	}
	174	/* Fall-through */
	175	case RCU_READER_INACTIVE:
	176	cds_list_move(&index->node, qsreaders);
	177	break;
	178	case RCU_READER_ACTIVE_OLD:
	179	/*
	180	* Old snapshot. Leaving node in
	181	* input_readers will make us busy-loop
	182	* until the snapshot becomes current or
	183	* the reader becomes inactive.
	184	*/
	185	break;
	186	}
	187	}
	188
	189	if (cds_list_empty(input_readers)) {
	190	if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
	191	/* Read reader_gp before write futex */
	192	cmm_smp_mb();
	193	uatomic_set(&rcu_gp.futex, 0);
	194	}
	195	break;
	196	} else {
	197	/* Temporarily unlock the registry lock. */
	198	mutex_unlock(&rcu_registry_lock);
	199	if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
	200	wait_gp();
	201	} else {
	202	#ifndef HAS_INCOHERENT_CACHES
	203	caa_cpu_relax();
	204	#else /* #ifndef HAS_INCOHERENT_CACHES */
	205	cmm_smp_mb();
	206	#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
	207	}
	208	/* Re-lock the registry lock before the next loop. */
	209	mutex_lock(&rcu_registry_lock);
	210	}
	211	}
	212	}
	213
	214	/*
	215	* Using a two-subphases algorithm for architectures with smaller than 64-bit
	216	* long-size to ensure we do not encounter an overflow bug.
	217	*/
	218
	219	#if (CAA_BITS_PER_LONG < 64)
	220	void synchronize_rcu(void)
	221	{
	222	CDS_LIST_HEAD(cur_snap_readers);
	223	CDS_LIST_HEAD(qsreaders);
	224	unsigned long was_online;
	225	DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
	226	struct urcu_waiters waiters;
	227
	228	was_online = rcu_read_ongoing();
	229
	230	/* All threads should read qparity before accessing data structure
	231	* where new ptr points to. In the "then" case, rcu_thread_offline
	232	* includes a memory barrier.
	233	*
	234	* Mark the writer thread offline to make sure we don't wait for
	235	* our own quiescent state. This allows using synchronize_rcu()
	236	* in threads registered as readers.
	237	*/
	238	if (was_online)
	239	rcu_thread_offline();
	240	else
	241	cmm_smp_mb();
	242
	243	/*
	244	* Add ourself to gp_waiters queue of threads awaiting to wait
	245	* for a grace period. Proceed to perform the grace period only
	246	* if we are the first thread added into the queue.
	247	*/
	248	if (urcu_wait_add(&gp_waiters, &wait) != 0) {
	249	/* Not first in queue: will be awakened by another thread. */
	250	urcu_adaptative_busy_wait(&wait);
	251	goto gp_end;
	252	}
	253	/* We won't need to wake ourself up */
	254	urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);
	255
	256	mutex_lock(&rcu_gp_lock);
	257
	258	/*
	259	* Move all waiters into our local queue.
	260	*/
	261	urcu_move_waiters(&waiters, &gp_waiters);
	262
	263	mutex_lock(&rcu_registry_lock);
	264
	265	if (cds_list_empty(&registry))
	266	goto out;
	267
	268	/*
	269	* Wait for readers to observe original parity or be quiescent.
	270	* wait_for_readers() can release and grab again rcu_registry_lock
	271	* interally.
	272	*/
	273	wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
	274
	275	/*
	276	* Must finish waiting for quiescent state for original parity
	277	* before committing next rcu_gp.ctr update to memory. Failure
	278	* to do so could result in the writer waiting forever while new
	279	* readers are always accessing data (no progress). Enforce
	280	* compiler-order of load URCU_TLS(rcu_reader).ctr before store
	281	* to rcu_gp.ctr.
	282	*/
	283	cmm_barrier();
	284
	285	/*
	286	* Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	287	* model easier to understand. It does not have a big performance impact
	288	* anyway, given this is the write-side.
	289	*/
	290	cmm_smp_mb();
	291
	292	/* Switch parity: 0 -> 1, 1 -> 0 */
	293	CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR);
	294
	295	/*
	296	* Must commit rcu_gp.ctr update to memory before waiting for
	297	* quiescent state. Failure to do so could result in the writer
	298	* waiting forever while new readers are always accessing data
	299	* (no progress). Enforce compiler-order of store to rcu_gp.ctr
	300	* before load URCU_TLS(rcu_reader).ctr.
	301	*/
	302	cmm_barrier();
	303
	304	/*
	305	* Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	306	* model easier to understand. It does not have a big performance impact
	307	* anyway, given this is the write-side.
	308	*/
	309	cmm_smp_mb();
	310
	311	/*
	312	* Wait for readers to observe new parity or be quiescent.
	313	* wait_for_readers() can release and grab again rcu_registry_lock
	314	* interally.
	315	*/
	316	wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
	317
	318	/*
	319	* Put quiescent reader list back into registry.
	320	*/
	321	cds_list_splice(&qsreaders, &registry);
	322	out:
	323	mutex_unlock(&rcu_registry_lock);
	324	mutex_unlock(&rcu_gp_lock);
	325	urcu_wake_all_waiters(&waiters);
	326	gp_end:
	327	/*
	328	* Finish waiting for reader threads before letting the old ptr being
	329	* freed.
	330	*/
	331	if (was_online)
	332	rcu_thread_online();
	333	else
	334	cmm_smp_mb();
	335	}
	336	#else /* !(CAA_BITS_PER_LONG < 64) */
	337	void synchronize_rcu(void)
	338	{
	339	CDS_LIST_HEAD(qsreaders);
	340	unsigned long was_online;
	341	DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
	342	struct urcu_waiters waiters;
	343
	344	was_online = rcu_read_ongoing();
	345
	346	/*
	347	* Mark the writer thread offline to make sure we don't wait for
	348	* our own quiescent state. This allows using synchronize_rcu()
	349	* in threads registered as readers.
	350	*/
	351	if (was_online)
	352	rcu_thread_offline();
	353	else
	354	cmm_smp_mb();
	355
	356	/*
	357	* Add ourself to gp_waiters queue of threads awaiting to wait
	358	* for a grace period. Proceed to perform the grace period only
	359	* if we are the first thread added into the queue.
	360	*/
	361	if (urcu_wait_add(&gp_waiters, &wait) != 0) {
	362	/* Not first in queue: will be awakened by another thread. */
	363	urcu_adaptative_busy_wait(&wait);
	364	goto gp_end;
	365	}
	366	/* We won't need to wake ourself up */
	367	urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);
	368
	369	mutex_lock(&rcu_gp_lock);
	370
	371	/*
	372	* Move all waiters into our local queue.
	373	*/
	374	urcu_move_waiters(&waiters, &gp_waiters);
	375
	376	mutex_lock(&rcu_registry_lock);
	377
	378	if (cds_list_empty(&registry))
	379	goto out;
	380
	381	/* Increment current G.P. */
	382	CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr + RCU_GP_CTR);
	383
	384	/*
	385	* Must commit rcu_gp.ctr update to memory before waiting for
	386	* quiescent state. Failure to do so could result in the writer
	387	* waiting forever while new readers are always accessing data
	388	* (no progress). Enforce compiler-order of store to rcu_gp.ctr
	389	* before load URCU_TLS(rcu_reader).ctr.
	390	*/
	391	cmm_barrier();
	392
	393	/*
	394	* Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	395	* model easier to understand. It does not have a big performance impact
	396	* anyway, given this is the write-side.
	397	*/
	398	cmm_smp_mb();
	399
	400	/*
	401	* Wait for readers to observe new count of be quiescent.
	402	* wait_for_readers() can release and grab again rcu_registry_lock
	403	* interally.
	404	*/
	405	wait_for_readers(&registry, NULL, &qsreaders);
	406
	407	/*
	408	* Put quiescent reader list back into registry.
	409	*/
	410	cds_list_splice(&qsreaders, &registry);
	411	out:
	412	mutex_unlock(&rcu_registry_lock);
	413	mutex_unlock(&rcu_gp_lock);
	414	urcu_wake_all_waiters(&waiters);
	415	gp_end:
	416	if (was_online)
	417	rcu_thread_online();
	418	else
	419	cmm_smp_mb();
	420	}
	421	#endif /* !(CAA_BITS_PER_LONG < 64) */
	422
	423	/*
	424	* library wrappers to be used by non-LGPL compatible source code.
	425	*/
	426
	427	void rcu_read_lock(void)
	428	{
	429	_rcu_read_lock();
	430	}
	431
	432	void rcu_read_unlock(void)
	433	{
	434	_rcu_read_unlock();
	435	}
	436
	437	int rcu_read_ongoing(void)
	438	{
	439	return _rcu_read_ongoing();
	440	}
	441
	442	void rcu_quiescent_state(void)
	443	{
	444	_rcu_quiescent_state();
	445	}
	446
	447	void rcu_thread_offline(void)
	448	{
	449	_rcu_thread_offline();
	450	}
	451
	452	void rcu_thread_online(void)
	453	{
	454	_rcu_thread_online();
	455	}
	456
	457	void rcu_register_thread(void)
	458	{
	459	URCU_TLS(rcu_reader).tid = pthread_self();
	460	assert(URCU_TLS(rcu_reader).ctr == 0);
	461
	462	mutex_lock(&rcu_registry_lock);
	463	cds_list_add(&URCU_TLS(rcu_reader).node, &registry);
	464	mutex_unlock(&rcu_registry_lock);
	465	_rcu_thread_online();
	466	}
	467
	468	void rcu_unregister_thread(void)
	469	{
	470	/*
	471	* We have to make the thread offline otherwise we end up dealocking
	472	* with a waiting writer.
	473	*/
	474	_rcu_thread_offline();
	475	mutex_lock(&rcu_registry_lock);
	476	cds_list_del(&URCU_TLS(rcu_reader).node);
	477	mutex_unlock(&rcu_registry_lock);
	478	}
	479
	480	void rcu_exit(void)
	481	{
	482	/*
	483	* Assertion disabled because call_rcu threads are now rcu
	484	* readers, and left running at exit.
	485	* assert(cds_list_empty(&registry));
	486	*/
	487	}
	488
	489	DEFINE_RCU_FLAVOR(rcu_flavor);
	490
	491	#include "urcu-call-rcu-impl.h"
	492	#include "urcu-defer-impl.h"