[urcu.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);

static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;

int32_t rcu_gp_futex;

/*
 * Global grace period counter.
 */
unsigned long 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(struct rcu_reader, rcu_reader);

#ifdef DEBUG_YIELD
unsigned int rcu_yield_active;
DEFINE_URCU_TLS(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);
}

static void wait_for_readers(struct cds_list_head *input_readers,
			struct cds_list_head *cur_snap_readers,
			struct cds_list_head *qsreaders)
{
	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 (;;) {
		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 {
			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 */
			}
		}
	}
}

/*
 * 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 = URCU_TLS(rcu_reader).ctr;

	/* 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);

	if (cds_list_empty(&registry))
		goto out;

	/*
	 * Wait for readers to observe original parity or be quiescent.
	 */
	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(&cur_snap_readers, NULL, &qsreaders);

	/*
	 * Put quiescent reader list back into registry.
	 */
	cds_list_splice(&qsreaders, &registry);
out:
	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 = URCU_TLS(rcu_reader).ctr;

	/*
	 * 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);

	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(&registry, NULL, &qsreaders);

	/*
	 * Put quiescent reader list back into registry.
	 */
	cds_list_splice(&qsreaders, &registry);
out:
	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();
}

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_gp_lock);
	cds_list_add(&URCU_TLS(rcu_reader).node, &registry);
	mutex_unlock(&rcu_gp_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_gp_lock);
	cds_list_del(&URCU_TLS(rcu_reader).node);
	mutex_unlock(&rcu_gp_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	static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
	56
	57	int32_t rcu_gp_futex;
	58
	59	/*
	60	* Global grace period counter.
	61	*/
	62	unsigned long rcu_gp_ctr = RCU_GP_ONLINE;
	63
	64	/*
	65	* Active attempts to check for reader Q.S. before calling futex().
	66	*/
	67	#define RCU_QS_ACTIVE_ATTEMPTS 100
	68
	69	/*
	70	* Written to only by each individual reader. Read by both the reader and the
	71	* writers.
	72	*/
	73	DEFINE_URCU_TLS(struct rcu_reader, rcu_reader);
	74
	75	#ifdef DEBUG_YIELD
	76	unsigned int rcu_yield_active;
	77	DEFINE_URCU_TLS(unsigned int, rcu_rand_yield);
	78	#endif
	79
	80	static CDS_LIST_HEAD(registry);
	81
	82	/*
	83	* Queue keeping threads awaiting to wait for a grace period. Contains
	84	* struct gp_waiters_thread objects.
	85	*/
	86	static DEFINE_URCU_WAIT_QUEUE(gp_waiters);
	87
	88	static void mutex_lock(pthread_mutex_t *mutex)
	89	{
	90	int ret;
	91
	92	#ifndef DISTRUST_SIGNALS_EXTREME
	93	ret = pthread_mutex_lock(mutex);
	94	if (ret)
	95	urcu_die(ret);
	96	#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	97	while ((ret = pthread_mutex_trylock(mutex)) != 0) {
	98	if (ret != EBUSY && ret != EINTR)
	99	urcu_die(ret);
	100	poll(NULL,0,10);
	101	}
	102	#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
	103	}
	104
	105	static void mutex_unlock(pthread_mutex_t *mutex)
	106	{
	107	int ret;
	108
	109	ret = pthread_mutex_unlock(mutex);
	110	if (ret)
	111	urcu_die(ret);
	112	}
	113
	114	/*
	115	* synchronize_rcu() waiting. Single thread.
	116	*/
	117	static void wait_gp(void)
	118	{
	119	/* Read reader_gp before read futex */
	120	cmm_smp_rmb();
	121	if (uatomic_read(&rcu_gp_futex) == -1)
	122	futex_noasync(&rcu_gp_futex, FUTEX_WAIT, -1,
	123	NULL, NULL, 0);
	124	}
	125
	126	static void wait_for_readers(struct cds_list_head *input_readers,
	127	struct cds_list_head *cur_snap_readers,
	128	struct cds_list_head *qsreaders)
	129	{
	130	int wait_loops = 0;
	131	struct rcu_reader index, tmp;
	132
	133	/*
	134	* Wait for each thread URCU_TLS(rcu_reader).ctr to either
	135	* indicate quiescence (offline), or for them to observe the
	136	* current rcu_gp_ctr value.
	137	*/
	138	for (;;) {
	139	wait_loops++;
	140	if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
	141	uatomic_set(&rcu_gp_futex, -1);
	142	/*
	143	* Write futex before write waiting (the other side
	144	* reads them in the opposite order).
	145	*/
	146	cmm_smp_wmb();
	147	cds_list_for_each_entry(index, input_readers, node) {
	148	_CMM_STORE_SHARED(index->waiting, 1);
	149	}
	150	/* Write futex before read reader_gp */
	151	cmm_smp_mb();
	152	}
	153	cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
	154	switch (rcu_reader_state(&index->ctr)) {
	155	case RCU_READER_ACTIVE_CURRENT:
	156	if (cur_snap_readers) {
	157	cds_list_move(&index->node,
	158	cur_snap_readers);
	159	break;
	160	}
	161	/* Fall-through */
	162	case RCU_READER_INACTIVE:
	163	cds_list_move(&index->node, qsreaders);
	164	break;
	165	case RCU_READER_ACTIVE_OLD:
	166	/*
	167	* Old snapshot. Leaving node in
	168	* input_readers will make us busy-loop
	169	* until the snapshot becomes current or
	170	* the reader becomes inactive.
	171	*/
	172	break;
	173	}
	174	}
	175
	176	if (cds_list_empty(input_readers)) {
	177	if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
	178	/* Read reader_gp before write futex */
	179	cmm_smp_mb();
	180	uatomic_set(&rcu_gp_futex, 0);
	181	}
	182	break;
	183	} else {
	184	if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
	185	wait_gp();
	186	} else {
	187	#ifndef HAS_INCOHERENT_CACHES
	188	caa_cpu_relax();
	189	#else /* #ifndef HAS_INCOHERENT_CACHES */
	190	cmm_smp_mb();
	191	#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
	192	}
	193	}
	194	}
	195	}
	196
	197	/*
	198	* Using a two-subphases algorithm for architectures with smaller than 64-bit
	199	* long-size to ensure we do not encounter an overflow bug.
	200	*/
	201
	202	#if (CAA_BITS_PER_LONG < 64)
	203	void synchronize_rcu(void)
	204	{
	205	CDS_LIST_HEAD(cur_snap_readers);
	206	CDS_LIST_HEAD(qsreaders);
	207	unsigned long was_online;
	208	DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
	209	struct urcu_waiters waiters;
	210
	211	was_online = URCU_TLS(rcu_reader).ctr;
	212
	213	/* All threads should read qparity before accessing data structure
	214	* where new ptr points to. In the "then" case, rcu_thread_offline
	215	* includes a memory barrier.
	216	*
	217	* Mark the writer thread offline to make sure we don't wait for
	218	* our own quiescent state. This allows using synchronize_rcu()
	219	* in threads registered as readers.
	220	*/
	221	if (was_online)
	222	rcu_thread_offline();
	223	else
	224	cmm_smp_mb();
	225
	226	/*
	227	* Add ourself to gp_waiters queue of threads awaiting to wait
	228	* for a grace period. Proceed to perform the grace period only
	229	* if we are the first thread added into the queue.
	230	*/
	231	if (urcu_wait_add(&gp_waiters, &wait) != 0) {
	232	/* Not first in queue: will be awakened by another thread. */
	233	urcu_adaptative_busy_wait(&wait);
	234	goto gp_end;
	235	}
	236	/* We won't need to wake ourself up */
	237	urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);
	238
	239	mutex_lock(&rcu_gp_lock);
	240
	241	/*
	242	* Move all waiters into our local queue.
	243	*/
	244	urcu_move_waiters(&waiters, &gp_waiters);
	245
	246	if (cds_list_empty(&registry))
	247	goto out;
	248
	249	/*
	250	* Wait for readers to observe original parity or be quiescent.
	251	*/
	252	wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
	253
	254	/*
	255	* Must finish waiting for quiescent state for original parity
	256	* before committing next rcu_gp_ctr update to memory. Failure
	257	* to do so could result in the writer waiting forever while new
	258	* readers are always accessing data (no progress). Enforce
	259	* compiler-order of load URCU_TLS(rcu_reader).ctr before store
	260	* to rcu_gp_ctr.
	261	*/
	262	cmm_barrier();
	263
	264	/*
	265	* Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	266	* model easier to understand. It does not have a big performance impact
	267	* anyway, given this is the write-side.
	268	*/
	269	cmm_smp_mb();
	270
	271	/* Switch parity: 0 -> 1, 1 -> 0 */
	272	CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR);
	273
	274	/*
	275	* Must commit rcu_gp_ctr update to memory before waiting for
	276	* quiescent state. Failure to do so could result in the writer
	277	* waiting forever while new readers are always accessing data
	278	* (no progress). Enforce compiler-order of store to rcu_gp_ctr
	279	* before load URCU_TLS(rcu_reader).ctr.
	280	*/
	281	cmm_barrier();
	282
	283	/*
	284	* Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	285	* model easier to understand. It does not have a big performance impact
	286	* anyway, given this is the write-side.
	287	*/
	288	cmm_smp_mb();
	289
	290	/*
	291	* Wait for readers to observe new parity or be quiescent.
	292	*/
	293	wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
	294
	295	/*
	296	* Put quiescent reader list back into registry.
	297	*/
	298	cds_list_splice(&qsreaders, &registry);
	299	out:
	300	mutex_unlock(&rcu_gp_lock);
	301	urcu_wake_all_waiters(&waiters);
	302	gp_end:
	303	/*
	304	* Finish waiting for reader threads before letting the old ptr being
	305	* freed.
	306	*/
	307	if (was_online)
	308	rcu_thread_online();
	309	else
	310	cmm_smp_mb();
	311	}
	312	#else /* !(CAA_BITS_PER_LONG < 64) */
	313	void synchronize_rcu(void)
	314	{
	315	CDS_LIST_HEAD(qsreaders);
	316	unsigned long was_online;
	317	DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
	318	struct urcu_waiters waiters;
	319
	320	was_online = URCU_TLS(rcu_reader).ctr;
	321
	322	/*
	323	* Mark the writer thread offline to make sure we don't wait for
	324	* our own quiescent state. This allows using synchronize_rcu()
	325	* in threads registered as readers.
	326	*/
	327	if (was_online)
	328	rcu_thread_offline();
	329	else
	330	cmm_smp_mb();
	331
	332	/*
	333	* Add ourself to gp_waiters queue of threads awaiting to wait
	334	* for a grace period. Proceed to perform the grace period only
	335	* if we are the first thread added into the queue.
	336	*/
	337	if (urcu_wait_add(&gp_waiters, &wait) != 0) {
	338	/* Not first in queue: will be awakened by another thread. */
	339	urcu_adaptative_busy_wait(&wait);
	340	goto gp_end;
	341	}
	342	/* We won't need to wake ourself up */
	343	urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);
	344
	345	mutex_lock(&rcu_gp_lock);
	346
	347	/*
	348	* Move all waiters into our local queue.
	349	*/
	350	urcu_move_waiters(&waiters, &gp_waiters);
	351
	352	if (cds_list_empty(&registry))
	353	goto out;
	354
	355	/* Increment current G.P. */
	356	CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR);
	357
	358	/*
	359	* Must commit rcu_gp_ctr update to memory before waiting for
	360	* quiescent state. Failure to do so could result in the writer
	361	* waiting forever while new readers are always accessing data
	362	* (no progress). Enforce compiler-order of store to rcu_gp_ctr
	363	* before load URCU_TLS(rcu_reader).ctr.
	364	*/
	365	cmm_barrier();
	366
	367	/*
	368	* Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	369	* model easier to understand. It does not have a big performance impact
	370	* anyway, given this is the write-side.
	371	*/
	372	cmm_smp_mb();
	373
	374	/*
	375	* Wait for readers to observe new count of be quiescent.
	376	*/
	377	wait_for_readers(&registry, NULL, &qsreaders);
	378
	379	/*
	380	* Put quiescent reader list back into registry.
	381	*/
	382	cds_list_splice(&qsreaders, &registry);
	383	out:
	384	mutex_unlock(&rcu_gp_lock);
	385	urcu_wake_all_waiters(&waiters);
	386	gp_end:
	387	if (was_online)
	388	rcu_thread_online();
	389	else
	390	cmm_smp_mb();
	391	}
	392	#endif /* !(CAA_BITS_PER_LONG < 64) */
	393
	394	/*
	395	* library wrappers to be used by non-LGPL compatible source code.
	396	*/
	397
	398	void rcu_read_lock(void)
	399	{
	400	_rcu_read_lock();
	401	}
	402
	403	void rcu_read_unlock(void)
	404	{
	405	_rcu_read_unlock();
	406	}
	407
	408	void rcu_quiescent_state(void)
	409	{
	410	_rcu_quiescent_state();
	411	}
	412
	413	void rcu_thread_offline(void)
	414	{
	415	_rcu_thread_offline();
	416	}
	417
	418	void rcu_thread_online(void)
	419	{
	420	_rcu_thread_online();
	421	}
	422
	423	void rcu_register_thread(void)
	424	{
	425	URCU_TLS(rcu_reader).tid = pthread_self();
	426	assert(URCU_TLS(rcu_reader).ctr == 0);
	427
	428	mutex_lock(&rcu_gp_lock);
	429	cds_list_add(&URCU_TLS(rcu_reader).node, &registry);
	430	mutex_unlock(&rcu_gp_lock);
	431	_rcu_thread_online();
	432	}
	433
	434	void rcu_unregister_thread(void)
	435	{
	436	/*
	437	* We have to make the thread offline otherwise we end up dealocking
	438	* with a waiting writer.
	439	*/
	440	_rcu_thread_offline();
	441	mutex_lock(&rcu_gp_lock);
	442	cds_list_del(&URCU_TLS(rcu_reader).node);
	443	mutex_unlock(&rcu_gp_lock);
	444	}
	445
	446	void rcu_exit(void)
	447	{
	448	/*
	449	* Assertion disabled because call_rcu threads are now rcu
	450	* readers, and left running at exit.
	451	* assert(cds_list_empty(&registry));
	452	*/
	453	}
	454
	455	DEFINE_RCU_FLAVOR(rcu_flavor);
	456
	457	#include "urcu-call-rcu-impl.h"
	458	#include "urcu-defer-impl.h"