[userspace-rcu.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
#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/map/urcu.h"

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

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