[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(struct rcu_reader, rcu_reader);

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)
		return;
	while (futex_noasync(&rcu_gp.futex, FUTEX_WAIT, -1,
			NULL, NULL, 0)) {
		switch (errno) {
		case EWOULDBLOCK:
			/* Value already changed. */
			return;
		case EINTR:
			/* Retry if interrupted by signal. */
			break;	/* Get out of switch. */
		default:
			/* Unexpected error. */
			urcu_die(errno);
		}
	}
}

/*
 * 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);
	assert(!URCU_TLS(rcu_reader).registered);
	URCU_TLS(rcu_reader).registered = 1;
	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();
	assert(URCU_TLS(rcu_reader).registered);
	URCU_TLS(rcu_reader).registered = 0;
	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(struct rcu_reader, rcu_reader);
	82
	83	static CDS_LIST_HEAD(registry);
	84
	85	/*
	86	* Queue keeping threads awaiting to wait for a grace period. Contains
	87	* struct gp_waiters_thread objects.
	88	*/
	89	static DEFINE_URCU_WAIT_QUEUE(gp_waiters);
	90
	91	static void mutex_lock(pthread_mutex_t *mutex)
	92	{
	93	int ret;
	94
	95	#ifndef DISTRUST_SIGNALS_EXTREME
	96	ret = pthread_mutex_lock(mutex);
	97	if (ret)
	98	urcu_die(ret);
	99	#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	100	while ((ret = pthread_mutex_trylock(mutex)) != 0) {
	101	if (ret != EBUSY && ret != EINTR)
	102	urcu_die(ret);
	103	poll(NULL,0,10);
	104	}
	105	#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
	106	}
	107
	108	static void mutex_unlock(pthread_mutex_t *mutex)
	109	{
	110	int ret;
	111
	112	ret = pthread_mutex_unlock(mutex);
	113	if (ret)
	114	urcu_die(ret);
	115	}
	116
	117	/*
	118	* synchronize_rcu() waiting. Single thread.
	119	*/
	120	static void wait_gp(void)
	121	{
	122	/* Read reader_gp before read futex */
	123	cmm_smp_rmb();
	124	if (uatomic_read(&rcu_gp.futex) != -1)
	125	return;
	126	while (futex_noasync(&rcu_gp.futex, FUTEX_WAIT, -1,
	127	NULL, NULL, 0)) {
	128	switch (errno) {
	129	case EWOULDBLOCK:
	130	/* Value already changed. */
	131	return;
	132	case EINTR:
	133	/* Retry if interrupted by signal. */
	134	break; /* Get out of switch. */
	135	default:
	136	/* Unexpected error. */
	137	urcu_die(errno);
	138	}
	139	}
	140	}
	141
	142	/*
	143	* Always called with rcu_registry lock held. Releases this lock between
	144	* iterations and grabs it again. Holds the lock when it returns.
	145	*/
	146	static void wait_for_readers(struct cds_list_head *input_readers,
	147	struct cds_list_head *cur_snap_readers,
	148	struct cds_list_head *qsreaders)
	149	{
	150	unsigned int wait_loops = 0;
	151	struct rcu_reader index, tmp;
	152
	153	/*
	154	* Wait for each thread URCU_TLS(rcu_reader).ctr to either
	155	* indicate quiescence (offline), or for them to observe the
	156	* current rcu_gp.ctr value.
	157	*/
	158	for (;;) {
	159	if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
	160	wait_loops++;
	161	if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
	162	uatomic_set(&rcu_gp.futex, -1);
	163	/*
	164	* Write futex before write waiting (the other side
	165	* reads them in the opposite order).
	166	*/
	167	cmm_smp_wmb();
	168	cds_list_for_each_entry(index, input_readers, node) {
	169	_CMM_STORE_SHARED(index->waiting, 1);
	170	}
	171	/* Write futex before read reader_gp */
	172	cmm_smp_mb();
	173	}
	174	cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
	175	switch (rcu_reader_state(&index->ctr)) {
	176	case RCU_READER_ACTIVE_CURRENT:
	177	if (cur_snap_readers) {
	178	cds_list_move(&index->node,
	179	cur_snap_readers);
	180	break;
	181	}
	182	/* Fall-through */
	183	case RCU_READER_INACTIVE:
	184	cds_list_move(&index->node, qsreaders);
	185	break;
	186	case RCU_READER_ACTIVE_OLD:
	187	/*
	188	* Old snapshot. Leaving node in
	189	* input_readers will make us busy-loop
	190	* until the snapshot becomes current or
	191	* the reader becomes inactive.
	192	*/
	193	break;
	194	}
	195	}
	196
	197	if (cds_list_empty(input_readers)) {
	198	if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
	199	/* Read reader_gp before write futex */
	200	cmm_smp_mb();
	201	uatomic_set(&rcu_gp.futex, 0);
	202	}
	203	break;
	204	} else {
	205	/* Temporarily unlock the registry lock. */
	206	mutex_unlock(&rcu_registry_lock);
	207	if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
	208	wait_gp();
	209	} else {
	210	#ifndef HAS_INCOHERENT_CACHES
	211	caa_cpu_relax();
	212	#else /* #ifndef HAS_INCOHERENT_CACHES */
	213	cmm_smp_mb();
	214	#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
	215	}
	216	/* Re-lock the registry lock before the next loop. */
	217	mutex_lock(&rcu_registry_lock);
	218	}
	219	}
	220	}
	221
	222	/*
	223	* Using a two-subphases algorithm for architectures with smaller than 64-bit
	224	* long-size to ensure we do not encounter an overflow bug.
	225	*/
	226
	227	#if (CAA_BITS_PER_LONG < 64)
	228	void synchronize_rcu(void)
	229	{
	230	CDS_LIST_HEAD(cur_snap_readers);
	231	CDS_LIST_HEAD(qsreaders);
	232	unsigned long was_online;
	233	DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
	234	struct urcu_waiters waiters;
	235
	236	was_online = rcu_read_ongoing();
	237
	238	/* All threads should read qparity before accessing data structure
	239	* where new ptr points to. In the "then" case, rcu_thread_offline
	240	* includes a memory barrier.
	241	*
	242	* Mark the writer thread offline to make sure we don't wait for
	243	* our own quiescent state. This allows using synchronize_rcu()
	244	* in threads registered as readers.
	245	*/
	246	if (was_online)
	247	rcu_thread_offline();
	248	else
	249	cmm_smp_mb();
	250
	251	/*
	252	* Add ourself to gp_waiters queue of threads awaiting to wait
	253	* for a grace period. Proceed to perform the grace period only
	254	* if we are the first thread added into the queue.
	255	*/
	256	if (urcu_wait_add(&gp_waiters, &wait) != 0) {
	257	/* Not first in queue: will be awakened by another thread. */
	258	urcu_adaptative_busy_wait(&wait);
	259	goto gp_end;
	260	}
	261	/* We won't need to wake ourself up */
	262	urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);
	263
	264	mutex_lock(&rcu_gp_lock);
	265
	266	/*
	267	* Move all waiters into our local queue.
	268	*/
	269	urcu_move_waiters(&waiters, &gp_waiters);
	270
	271	mutex_lock(&rcu_registry_lock);
	272
	273	if (cds_list_empty(&registry))
	274	goto out;
	275
	276	/*
	277	* Wait for readers to observe original parity or be quiescent.
	278	* wait_for_readers() can release and grab again rcu_registry_lock
	279	* interally.
	280	*/
	281	wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
	282
	283	/*
	284	* Must finish waiting for quiescent state for original parity
	285	* before committing next rcu_gp.ctr update to memory. Failure
	286	* to do so could result in the writer waiting forever while new
	287	* readers are always accessing data (no progress). Enforce
	288	* compiler-order of load URCU_TLS(rcu_reader).ctr before store
	289	* to rcu_gp.ctr.
	290	*/
	291	cmm_barrier();
	292
	293	/*
	294	* Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	295	* model easier to understand. It does not have a big performance impact
	296	* anyway, given this is the write-side.
	297	*/
	298	cmm_smp_mb();
	299
	300	/* Switch parity: 0 -> 1, 1 -> 0 */
	301	CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR);
	302
	303	/*
	304	* Must commit rcu_gp.ctr update to memory before waiting for
	305	* quiescent state. Failure to do so could result in the writer
	306	* waiting forever while new readers are always accessing data
	307	* (no progress). Enforce compiler-order of store to rcu_gp.ctr
	308	* before load URCU_TLS(rcu_reader).ctr.
	309	*/
	310	cmm_barrier();
	311
	312	/*
	313	* Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	314	* model easier to understand. It does not have a big performance impact
	315	* anyway, given this is the write-side.
	316	*/
	317	cmm_smp_mb();
	318
	319	/*
	320	* Wait for readers to observe new parity or be quiescent.
	321	* wait_for_readers() can release and grab again rcu_registry_lock
	322	* interally.
	323	*/
	324	wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
	325
	326	/*
	327	* Put quiescent reader list back into registry.
	328	*/
	329	cds_list_splice(&qsreaders, &registry);
	330	out:
	331	mutex_unlock(&rcu_registry_lock);
	332	mutex_unlock(&rcu_gp_lock);
	333	urcu_wake_all_waiters(&waiters);
	334	gp_end:
	335	/*
	336	* Finish waiting for reader threads before letting the old ptr being
	337	* freed.
	338	*/
	339	if (was_online)
	340	rcu_thread_online();
	341	else
	342	cmm_smp_mb();
	343	}
	344	#else /* !(CAA_BITS_PER_LONG < 64) */
	345	void synchronize_rcu(void)
	346	{
	347	CDS_LIST_HEAD(qsreaders);
	348	unsigned long was_online;
	349	DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
	350	struct urcu_waiters waiters;
	351
	352	was_online = rcu_read_ongoing();
	353
	354	/*
	355	* Mark the writer thread offline to make sure we don't wait for
	356	* our own quiescent state. This allows using synchronize_rcu()
	357	* in threads registered as readers.
	358	*/
	359	if (was_online)
	360	rcu_thread_offline();
	361	else
	362	cmm_smp_mb();
	363
	364	/*
	365	* Add ourself to gp_waiters queue of threads awaiting to wait
	366	* for a grace period. Proceed to perform the grace period only
	367	* if we are the first thread added into the queue.
	368	*/
	369	if (urcu_wait_add(&gp_waiters, &wait) != 0) {
	370	/* Not first in queue: will be awakened by another thread. */
	371	urcu_adaptative_busy_wait(&wait);
	372	goto gp_end;
	373	}
	374	/* We won't need to wake ourself up */
	375	urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);
	376
	377	mutex_lock(&rcu_gp_lock);
	378
	379	/*
	380	* Move all waiters into our local queue.
	381	*/
	382	urcu_move_waiters(&waiters, &gp_waiters);
	383
	384	mutex_lock(&rcu_registry_lock);
	385
	386	if (cds_list_empty(&registry))
	387	goto out;
	388
	389	/* Increment current G.P. */
	390	CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr + RCU_GP_CTR);
	391
	392	/*
	393	* Must commit rcu_gp.ctr update to memory before waiting for
	394	* quiescent state. Failure to do so could result in the writer
	395	* waiting forever while new readers are always accessing data
	396	* (no progress). Enforce compiler-order of store to rcu_gp.ctr
	397	* before load URCU_TLS(rcu_reader).ctr.
	398	*/
	399	cmm_barrier();
	400
	401	/*
	402	* Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	403	* model easier to understand. It does not have a big performance impact
	404	* anyway, given this is the write-side.
	405	*/
	406	cmm_smp_mb();
	407
	408	/*
	409	* Wait for readers to observe new count of be quiescent.
	410	* wait_for_readers() can release and grab again rcu_registry_lock
	411	* interally.
	412	*/
	413	wait_for_readers(&registry, NULL, &qsreaders);
	414
	415	/*
	416	* Put quiescent reader list back into registry.
	417	*/
	418	cds_list_splice(&qsreaders, &registry);
	419	out:
	420	mutex_unlock(&rcu_registry_lock);
	421	mutex_unlock(&rcu_gp_lock);
	422	urcu_wake_all_waiters(&waiters);
	423	gp_end:
	424	if (was_online)
	425	rcu_thread_online();
	426	else
	427	cmm_smp_mb();
	428	}
	429	#endif /* !(CAA_BITS_PER_LONG < 64) */
	430
	431	/*
	432	* library wrappers to be used by non-LGPL compatible source code.
	433	*/
	434
	435	void rcu_read_lock(void)
	436	{
	437	_rcu_read_lock();
	438	}
	439
	440	void rcu_read_unlock(void)
	441	{
	442	_rcu_read_unlock();
	443	}
	444
	445	int rcu_read_ongoing(void)
	446	{
	447	return _rcu_read_ongoing();
	448	}
	449
	450	void rcu_quiescent_state(void)
	451	{
	452	_rcu_quiescent_state();
	453	}
	454
	455	void rcu_thread_offline(void)
	456	{
	457	_rcu_thread_offline();
	458	}
	459
	460	void rcu_thread_online(void)
	461	{
	462	_rcu_thread_online();
	463	}
	464
	465	void rcu_register_thread(void)
	466	{
	467	URCU_TLS(rcu_reader).tid = pthread_self();
	468	assert(URCU_TLS(rcu_reader).ctr == 0);
	469
	470	mutex_lock(&rcu_registry_lock);
	471	assert(!URCU_TLS(rcu_reader).registered);
	472	URCU_TLS(rcu_reader).registered = 1;
	473	cds_list_add(&URCU_TLS(rcu_reader).node, &registry);
	474	mutex_unlock(&rcu_registry_lock);
	475	_rcu_thread_online();
	476	}
	477
	478	void rcu_unregister_thread(void)
	479	{
	480	/*
	481	* We have to make the thread offline otherwise we end up dealocking
	482	* with a waiting writer.
	483	*/
	484	_rcu_thread_offline();
	485	assert(URCU_TLS(rcu_reader).registered);
	486	URCU_TLS(rcu_reader).registered = 0;
	487	mutex_lock(&rcu_registry_lock);
	488	cds_list_del(&URCU_TLS(rcu_reader).node);
	489	mutex_unlock(&rcu_registry_lock);
	490	}
	491
	492	void rcu_exit(void)
	493	{
	494	/*
	495	* Assertion disabled because call_rcu threads are now rcu
	496	* readers, and left running at exit.
	497	* assert(cds_list_empty(&registry));
	498	*/
	499	}
	500
	501	DEFINE_RCU_FLAVOR(rcu_flavor);
	502
	503	#include "urcu-call-rcu-impl.h"
	504	#include "urcu-defer-impl.h"