[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"

/* 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 (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 */

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