[urcu.git] / urcu.c

/*
 * urcu.c
 *
 * Userspace RCU 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 _BSD_SOURCE
#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/wfqueue.h"
#include "urcu/map/urcu.h"
#include "urcu/static/urcu.h"
#include "urcu-pointer.h"

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

/*
 * If a reader is really non-cooperative and refuses to commit its
 * rcu_active_readers count to memory (there is no barrier in the reader
 * per-se), kick it after a few loops waiting for it.
 */
#define KICK_READER_LOOPS 10000

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

#ifdef RCU_MEMBARRIER
static int init_done;
int has_sys_membarrier;

void __attribute__((constructor)) rcu_init(void);
#endif

#ifdef RCU_MB
void rcu_init(void)
{
}
#endif

#ifdef RCU_SIGNAL
static int init_done;

void __attribute__((constructor)) rcu_init(void);
void __attribute__((destructor)) rcu_exit(void);
#endif

static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;

int32_t gp_futex;

/*
 * Global grace period counter.
 * Contains the current RCU_GP_CTR_PHASE.
 * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
 * Written to only by writer with mutex taken. Read by both writer and readers.
 */
unsigned long rcu_gp_ctr = RCU_GP_COUNT;

/*
 * Written to only by each individual reader. Read by both the reader and the
 * writers.
 */
struct rcu_reader __thread rcu_reader;

#ifdef DEBUG_YIELD
unsigned int yield_active;
unsigned int __thread rand_yield;
#endif

static CDS_LIST_HEAD(registry);

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

#ifndef DISTRUST_SIGNALS_EXTREME
	ret = pthread_mutex_lock(mutex);
	if (ret) {
		perror("Error in pthread mutex lock");
		exit(-1);
	}
#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	while ((ret = pthread_mutex_trylock(mutex)) != 0) {
		if (ret != EBUSY && ret != EINTR) {
			printf("ret = %d, errno = %d\n", ret, errno);
			perror("Error in pthread mutex lock");
			exit(-1);
		}
		if (CMM_LOAD_SHARED(rcu_reader.need_mb)) {
			cmm_smp_mb();
			_CMM_STORE_SHARED(rcu_reader.need_mb, 0);
			cmm_smp_mb();
		}
		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) {
		perror("Error in pthread mutex unlock");
		exit(-1);
	}
}

#ifdef RCU_MEMBARRIER
static void smp_mb_master(int group)
{
	if (caa_likely(has_sys_membarrier))
		membarrier(MEMBARRIER_EXPEDITED);
	else
		cmm_smp_mb();
}
#endif

#ifdef RCU_MB
static void smp_mb_master(int group)
{
	cmm_smp_mb();
}
#endif

#ifdef RCU_SIGNAL
static void force_mb_all_readers(void)
{
	struct rcu_reader *index;

	/*
	 * Ask for each threads to execute a cmm_smp_mb() so we can consider the
	 * compiler barriers around rcu read lock as real memory barriers.
	 */
	if (cds_list_empty(&registry))
		return;
	/*
	 * pthread_kill has a cmm_smp_mb(). But beware, we assume it performs
	 * a cache flush on architectures with non-coherent cache. Let's play
	 * safe and don't assume anything : we use cmm_smp_mc() to make sure the
	 * cache flush is enforced.
	 */
	cds_list_for_each_entry(index, &registry, node) {
		CMM_STORE_SHARED(index->need_mb, 1);
		pthread_kill(index->tid, SIGRCU);
	}
	/*
	 * Wait for sighandler (and thus mb()) to execute on every thread.
	 *
	 * Note that the pthread_kill() will never be executed on systems
	 * that correctly deliver signals in a timely manner.  However, it
	 * is not uncommon for kernels to have bugs that can result in
	 * lost or unduly delayed signals.
	 *
	 * If you are seeing the below pthread_kill() executing much at
	 * all, we suggest testing the underlying kernel and filing the
	 * relevant bug report.  For Linux kernels, we recommend getting
	 * the Linux Test Project (LTP).
	 */
	cds_list_for_each_entry(index, &registry, node) {
		while (CMM_LOAD_SHARED(index->need_mb)) {
			pthread_kill(index->tid, SIGRCU);
			poll(NULL, 0, 1);
		}
	}
	cmm_smp_mb();	/* read ->need_mb before ending the barrier */
}

static void smp_mb_master(int group)
{
	force_mb_all_readers();
}
#endif /* #ifdef RCU_SIGNAL */

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

void update_counter_and_wait(void)
{
	CDS_LIST_HEAD(qsreaders);
	int wait_loops = 0;
	struct rcu_reader *index, *tmp;

	/* Switch parity: 0 -> 1, 1 -> 0 */
	CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);

	/*
	 * 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 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 each thread rcu_reader.ctr count to become 0.
	 */
	for (;;) {
		wait_loops++;
		if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
			uatomic_dec(&gp_futex);
			/* Write futex before read reader_gp */
			smp_mb_master(RCU_MB_GROUP);
		}

		cds_list_for_each_entry_safe(index, tmp, &registry, node) {
			if (!rcu_gp_ongoing(&index->ctr))
				cds_list_move(&index->node, &qsreaders);
		}

#ifndef HAS_INCOHERENT_CACHES
		if (cds_list_empty(&registry)) {
			if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
				/* Read reader_gp before write futex */
				smp_mb_master(RCU_MB_GROUP);
				uatomic_set(&gp_futex, 0);
			}
			break;
		} else {
			if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
				wait_gp();
			else
				caa_cpu_relax();
		}
#else /* #ifndef HAS_INCOHERENT_CACHES */
		/*
		 * BUSY-LOOP. Force the reader thread to commit its
		 * rcu_reader.ctr update to memory if we wait for too long.
		 */
		if (cds_list_empty(&registry)) {
			if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
				/* Read reader_gp before write futex */
				smp_mb_master(RCU_MB_GROUP);
				uatomic_set(&gp_futex, 0);
			}
			break;
		} else {
			switch (wait_loops) {
			case RCU_QS_ACTIVE_ATTEMPTS:
				wait_gp();
				break; /* only escape switch */
			case KICK_READER_LOOPS:
				smp_mb_master(RCU_MB_GROUP);
				wait_loops = 0;
				break; /* only escape switch */
			default:
				caa_cpu_relax();
			}
		}
#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
	}
	/* put back the reader list in the registry */
	cds_list_splice(&qsreaders, &registry);
}

void synchronize_rcu(void)
{
	mutex_lock(&rcu_gp_lock);

	if (cds_list_empty(&registry))
		goto out;

	/* All threads should read qparity before accessing data structure
	 * where new ptr points to. Must be done within rcu_gp_lock because it
	 * iterates on reader threads.*/
	/* Write new ptr before changing the qparity */
	smp_mb_master(RCU_MB_GROUP);

	/*
	 * Wait for previous parity to be empty of readers.
	 */
	update_counter_and_wait();	/* 0 -> 1, wait readers in parity 0 */

	/*
	 * Must finish waiting for quiescent state for parity 0 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
	 * 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();

	/*
	 * Wait for previous parity to be empty of readers.
	 */
	update_counter_and_wait();	/* 1 -> 0, wait readers in parity 1 */

	/* Finish waiting for reader threads before letting the old ptr being
	 * freed. Must be done within rcu_gp_lock because it iterates on reader
	 * threads. */
	smp_mb_master(RCU_MB_GROUP);
out:
	mutex_unlock(&rcu_gp_lock);
}

/*
 * 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_register_thread(void)
{
	rcu_reader.tid = pthread_self();
	assert(rcu_reader.need_mb == 0);
	assert(!(rcu_reader.ctr & RCU_GP_CTR_NEST_MASK));

	mutex_lock(&rcu_gp_lock);
	rcu_init();	/* In case gcc does not support constructor attribute */
	cds_list_add(&rcu_reader.node, &registry);
	mutex_unlock(&rcu_gp_lock);
}

void rcu_unregister_thread(void)
{
	mutex_lock(&rcu_gp_lock);
	cds_list_del(&rcu_reader.node);
	mutex_unlock(&rcu_gp_lock);
}

#ifdef RCU_MEMBARRIER
void rcu_init(void)
{
	if (init_done)
		return;
	init_done = 1;
	if (!membarrier(MEMBARRIER_EXPEDITED | MEMBARRIER_QUERY))
		has_sys_membarrier = 1;
}
#endif

#ifdef RCU_SIGNAL
static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context)
{
	/*
	 * Executing this cmm_smp_mb() is the only purpose of this signal handler.
	 * It punctually promotes cmm_barrier() into cmm_smp_mb() on every thread it is
	 * executed on.
	 */
	cmm_smp_mb();
	_CMM_STORE_SHARED(rcu_reader.need_mb, 0);
	cmm_smp_mb();
}

/*
 * rcu_init constructor. Called when the library is linked, but also when
 * reader threads are calling rcu_register_thread().
 * Should only be called by a single thread at a given time. This is ensured by
 * holing the rcu_gp_lock from rcu_register_thread() or by running at library
 * load time, which should not be executed by multiple threads nor concurrently
 * with rcu_register_thread() anyway.
 */
void rcu_init(void)
{
	struct sigaction act;
	int ret;

	if (init_done)
		return;
	init_done = 1;

	act.sa_sigaction = sigrcu_handler;
	act.sa_flags = SA_SIGINFO | SA_RESTART;
	sigemptyset(&act.sa_mask);
	ret = sigaction(SIGRCU, &act, NULL);
	if (ret) {
		perror("Error in sigaction");
		exit(-1);
	}
}

void rcu_exit(void)
{
	struct sigaction act;
	int ret;

	ret = sigaction(SIGRCU, NULL, &act);
	if (ret) {
		perror("Error in sigaction");
		exit(-1);
	}
	assert(act.sa_sigaction == sigrcu_handler);
	assert(cds_list_empty(&registry));
}

#endif /* #ifdef RCU_SIGNAL */

DEFINE_RCU_FLAVOR(rcu_flavor);

#include "urcu-call-rcu-impl.h"
#include "urcu-defer-impl.h"
Commit	Line	Data
	1	/*
	2	* urcu.c
	3	*
	4	* Userspace RCU 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 _BSD_SOURCE
	27	#define _GNU_SOURCE
	28	#define _LGPL_SOURCE
	29	#include <stdio.h>
	30	#include <pthread.h>
	31	#include <signal.h>
	32	#include <assert.h>
	33	#include <stdlib.h>
	34	#include <stdint.h>
	35	#include <string.h>
	36	#include <errno.h>
	37	#include <poll.h>
	38
	39	#include "urcu/wfqueue.h"
	40	#include "urcu/map/urcu.h"
	41	#include "urcu/static/urcu.h"
	42	#include "urcu-pointer.h"
	43
	44	/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
	45	#undef _LGPL_SOURCE
	46	#include "urcu.h"
	47	#define _LGPL_SOURCE
	48
	49	/*
	50	* If a reader is really non-cooperative and refuses to commit its
	51	* rcu_active_readers count to memory (there is no barrier in the reader
	52	* per-se), kick it after a few loops waiting for it.
	53	*/
	54	#define KICK_READER_LOOPS 10000
	55
	56	/*
	57	* Active attempts to check for reader Q.S. before calling futex().
	58	*/
	59	#define RCU_QS_ACTIVE_ATTEMPTS 100
	60
	61	#ifdef RCU_MEMBARRIER
	62	static int init_done;
	63	int has_sys_membarrier;
	64
	65	void __attribute__((constructor)) rcu_init(void);
	66	#endif
	67
	68	#ifdef RCU_MB
	69	void rcu_init(void)
	70	{
	71	}
	72	#endif
	73
	74	#ifdef RCU_SIGNAL
	75	static int init_done;
	76
	77	void __attribute__((constructor)) rcu_init(void);
	78	void __attribute__((destructor)) rcu_exit(void);
	79	#endif
	80
	81	static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
	82
	83	int32_t gp_futex;
	84
	85	/*
	86	* Global grace period counter.
	87	* Contains the current RCU_GP_CTR_PHASE.
	88	* Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
	89	* Written to only by writer with mutex taken. Read by both writer and readers.
	90	*/
	91	unsigned long rcu_gp_ctr = RCU_GP_COUNT;
	92
	93	/*
	94	* Written to only by each individual reader. Read by both the reader and the
	95	* writers.
	96	*/
	97	struct rcu_reader __thread rcu_reader;
	98
	99	#ifdef DEBUG_YIELD
	100	unsigned int yield_active;
	101	unsigned int __thread rand_yield;
	102	#endif
	103
	104	static CDS_LIST_HEAD(registry);
	105
	106	static void mutex_lock(pthread_mutex_t *mutex)
	107	{
	108	int ret;
	109
	110	#ifndef DISTRUST_SIGNALS_EXTREME
	111	ret = pthread_mutex_lock(mutex);
	112	if (ret) {
	113	perror("Error in pthread mutex lock");
	114	exit(-1);
	115	}
	116	#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	117	while ((ret = pthread_mutex_trylock(mutex)) != 0) {
	118	if (ret != EBUSY && ret != EINTR) {
	119	printf("ret = %d, errno = %d\n", ret, errno);
	120	perror("Error in pthread mutex lock");
	121	exit(-1);
	122	}
	123	if (CMM_LOAD_SHARED(rcu_reader.need_mb)) {
	124	cmm_smp_mb();
	125	_CMM_STORE_SHARED(rcu_reader.need_mb, 0);
	126	cmm_smp_mb();
	127	}
	128	poll(NULL,0,10);
	129	}
	130	#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
	131	}
	132
	133	static void mutex_unlock(pthread_mutex_t *mutex)
	134	{
	135	int ret;
	136
	137	ret = pthread_mutex_unlock(mutex);
	138	if (ret) {
	139	perror("Error in pthread mutex unlock");
	140	exit(-1);
	141	}
	142	}
	143
	144	#ifdef RCU_MEMBARRIER
	145	static void smp_mb_master(int group)
	146	{
	147	if (caa_likely(has_sys_membarrier))
	148	membarrier(MEMBARRIER_EXPEDITED);
	149	else
	150	cmm_smp_mb();
	151	}
	152	#endif
	153
	154	#ifdef RCU_MB
	155	static void smp_mb_master(int group)
	156	{
	157	cmm_smp_mb();
	158	}
	159	#endif
	160
	161	#ifdef RCU_SIGNAL
	162	static void force_mb_all_readers(void)
	163	{
	164	struct rcu_reader *index;
	165
	166	/*
	167	* Ask for each threads to execute a cmm_smp_mb() so we can consider the
	168	* compiler barriers around rcu read lock as real memory barriers.
	169	*/
	170	if (cds_list_empty(&registry))
	171	return;
	172	/*
	173	* pthread_kill has a cmm_smp_mb(). But beware, we assume it performs
	174	* a cache flush on architectures with non-coherent cache. Let's play
	175	* safe and don't assume anything : we use cmm_smp_mc() to make sure the
	176	* cache flush is enforced.
	177	*/
	178	cds_list_for_each_entry(index, &registry, node) {
	179	CMM_STORE_SHARED(index->need_mb, 1);
	180	pthread_kill(index->tid, SIGRCU);
	181	}
	182	/*
	183	* Wait for sighandler (and thus mb()) to execute on every thread.
	184	*
	185	* Note that the pthread_kill() will never be executed on systems
	186	* that correctly deliver signals in a timely manner. However, it
	187	* is not uncommon for kernels to have bugs that can result in
	188	* lost or unduly delayed signals.
	189	*
	190	* If you are seeing the below pthread_kill() executing much at
	191	* all, we suggest testing the underlying kernel and filing the
	192	* relevant bug report. For Linux kernels, we recommend getting
	193	* the Linux Test Project (LTP).
	194	*/
	195	cds_list_for_each_entry(index, &registry, node) {
	196	while (CMM_LOAD_SHARED(index->need_mb)) {
	197	pthread_kill(index->tid, SIGRCU);
	198	poll(NULL, 0, 1);
	199	}
	200	}
	201	cmm_smp_mb(); /* read ->need_mb before ending the barrier */
	202	}
	203
	204	static void smp_mb_master(int group)
	205	{
	206	force_mb_all_readers();
	207	}
	208	#endif /* #ifdef RCU_SIGNAL */
	209
	210	/*
	211	* synchronize_rcu() waiting. Single thread.
	212	*/
	213	static void wait_gp(void)
	214	{
	215	/* Read reader_gp before read futex */
	216	smp_mb_master(RCU_MB_GROUP);
	217	if (uatomic_read(&gp_futex) == -1)
	218	futex_async(&gp_futex, FUTEX_WAIT, -1,
	219	NULL, NULL, 0);
	220	}
	221
	222	void update_counter_and_wait(void)
	223	{
	224	CDS_LIST_HEAD(qsreaders);
	225	int wait_loops = 0;
	226	struct rcu_reader index, tmp;
	227
	228	/* Switch parity: 0 -> 1, 1 -> 0 */
	229	CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
	230
	231	/*
	232	* Must commit rcu_gp_ctr update to memory before waiting for quiescent
	233	* state. Failure to do so could result in the writer waiting forever
	234	* while new readers are always accessing data (no progress). Enforce
	235	* compiler-order of store to rcu_gp_ctr before load rcu_reader ctr.
	236	*/
	237	cmm_barrier();
	238
	239	/*
	240	*
	241	* Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	242	* model easier to understand. It does not have a big performance impact
	243	* anyway, given this is the write-side.
	244	*/
	245	cmm_smp_mb();
	246
	247	/*
	248	* Wait for each thread rcu_reader.ctr count to become 0.
	249	*/
	250	for (;;) {
	251	wait_loops++;
	252	if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
	253	uatomic_dec(&gp_futex);
	254	/* Write futex before read reader_gp */
	255	smp_mb_master(RCU_MB_GROUP);
	256	}
	257
	258	cds_list_for_each_entry_safe(index, tmp, &registry, node) {
	259	if (!rcu_gp_ongoing(&index->ctr))
	260	cds_list_move(&index->node, &qsreaders);
	261	}
	262
	263	#ifndef HAS_INCOHERENT_CACHES
	264	if (cds_list_empty(&registry)) {
	265	if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
	266	/* Read reader_gp before write futex */
	267	smp_mb_master(RCU_MB_GROUP);
	268	uatomic_set(&gp_futex, 0);
	269	}
	270	break;
	271	} else {
	272	if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
	273	wait_gp();
	274	else
	275	caa_cpu_relax();
	276	}
	277	#else /* #ifndef HAS_INCOHERENT_CACHES */
	278	/*
	279	* BUSY-LOOP. Force the reader thread to commit its
	280	* rcu_reader.ctr update to memory if we wait for too long.
	281	*/
	282	if (cds_list_empty(&registry)) {
	283	if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
	284	/* Read reader_gp before write futex */
	285	smp_mb_master(RCU_MB_GROUP);
	286	uatomic_set(&gp_futex, 0);
	287	}
	288	break;
	289	} else {
	290	switch (wait_loops) {
	291	case RCU_QS_ACTIVE_ATTEMPTS:
	292	wait_gp();
	293	break; /* only escape switch */
	294	case KICK_READER_LOOPS:
	295	smp_mb_master(RCU_MB_GROUP);
	296	wait_loops = 0;
	297	break; /* only escape switch */
	298	default:
	299	caa_cpu_relax();
	300	}
	301	}
	302	#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
	303	}
	304	/* put back the reader list in the registry */
	305	cds_list_splice(&qsreaders, &registry);
	306	}
	307
	308	void synchronize_rcu(void)
	309	{
	310	mutex_lock(&rcu_gp_lock);
	311
	312	if (cds_list_empty(&registry))
	313	goto out;
	314
	315	/* All threads should read qparity before accessing data structure
	316	* where new ptr points to. Must be done within rcu_gp_lock because it
	317	* iterates on reader threads.*/
	318	/* Write new ptr before changing the qparity */
	319	smp_mb_master(RCU_MB_GROUP);
	320
	321	/*
	322	* Wait for previous parity to be empty of readers.
	323	*/
	324	update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */
	325
	326	/*
	327	* Must finish waiting for quiescent state for parity 0 before
	328	* committing next rcu_gp_ctr update to memory. Failure to do so could
	329	* result in the writer waiting forever while new readers are always
	330	* accessing data (no progress). Enforce compiler-order of load
	331	* rcu_reader ctr before store to rcu_gp_ctr.
	332	*/
	333	cmm_barrier();
	334
	335	/*
	336	* Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	337	* model easier to understand. It does not have a big performance impact
	338	* anyway, given this is the write-side.
	339	*/
	340	cmm_smp_mb();
	341
	342	/*
	343	* Wait for previous parity to be empty of readers.
	344	*/
	345	update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */
	346
	347	/* Finish waiting for reader threads before letting the old ptr being
	348	* freed. Must be done within rcu_gp_lock because it iterates on reader
	349	* threads. */
	350	smp_mb_master(RCU_MB_GROUP);
	351	out:
	352	mutex_unlock(&rcu_gp_lock);
	353	}
	354
	355	/*
	356	* library wrappers to be used by non-LGPL compatible source code.
	357	*/
	358
	359	void rcu_read_lock(void)
	360	{
	361	_rcu_read_lock();
	362	}
	363
	364	void rcu_read_unlock(void)
	365	{
	366	_rcu_read_unlock();
	367	}
	368
	369	void rcu_register_thread(void)
	370	{
	371	rcu_reader.tid = pthread_self();
	372	assert(rcu_reader.need_mb == 0);
	373	assert(!(rcu_reader.ctr & RCU_GP_CTR_NEST_MASK));
	374
	375	mutex_lock(&rcu_gp_lock);
	376	rcu_init(); /* In case gcc does not support constructor attribute */
	377	cds_list_add(&rcu_reader.node, &registry);
	378	mutex_unlock(&rcu_gp_lock);
	379	}
	380
	381	void rcu_unregister_thread(void)
	382	{
	383	mutex_lock(&rcu_gp_lock);
	384	cds_list_del(&rcu_reader.node);
	385	mutex_unlock(&rcu_gp_lock);
	386	}
	387
	388	#ifdef RCU_MEMBARRIER
	389	void rcu_init(void)
	390	{
	391	if (init_done)
	392	return;
	393	init_done = 1;
	394	if (!membarrier(MEMBARRIER_EXPEDITED \| MEMBARRIER_QUERY))
	395	has_sys_membarrier = 1;
	396	}
	397	#endif
	398
	399	#ifdef RCU_SIGNAL
	400	static void sigrcu_handler(int signo, siginfo_t siginfo, void context)
	401	{
	402	/*
	403	* Executing this cmm_smp_mb() is the only purpose of this signal handler.
	404	* It punctually promotes cmm_barrier() into cmm_smp_mb() on every thread it is
	405	* executed on.
	406	*/
	407	cmm_smp_mb();
	408	_CMM_STORE_SHARED(rcu_reader.need_mb, 0);
	409	cmm_smp_mb();
	410	}
	411
	412	/*
	413	* rcu_init constructor. Called when the library is linked, but also when
	414	* reader threads are calling rcu_register_thread().
	415	* Should only be called by a single thread at a given time. This is ensured by
	416	* holing the rcu_gp_lock from rcu_register_thread() or by running at library
	417	* load time, which should not be executed by multiple threads nor concurrently
	418	* with rcu_register_thread() anyway.
	419	*/
	420	void rcu_init(void)
	421	{
	422	struct sigaction act;
	423	int ret;
	424
	425	if (init_done)
	426	return;
	427	init_done = 1;
	428
	429	act.sa_sigaction = sigrcu_handler;
	430	act.sa_flags = SA_SIGINFO \| SA_RESTART;
	431	sigemptyset(&act.sa_mask);
	432	ret = sigaction(SIGRCU, &act, NULL);
	433	if (ret) {
	434	perror("Error in sigaction");
	435	exit(-1);
	436	}
	437	}
	438
	439	void rcu_exit(void)
	440	{
	441	struct sigaction act;
	442	int ret;
	443
	444	ret = sigaction(SIGRCU, NULL, &act);
	445	if (ret) {
	446	perror("Error in sigaction");
	447	exit(-1);
	448	}
	449	assert(act.sa_sigaction == sigrcu_handler);
	450	assert(cds_list_empty(&registry));
	451	}
	452
	453	#endif /* #ifdef RCU_SIGNAL */
	454
	455	DEFINE_RCU_FLAVOR(rcu_flavor);
	456
	457	#include "urcu-call-rcu-impl.h"
	458	#include "urcu-defer-impl.h"