[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
#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"
#include "urcu/tls-compat.h"

#include "urcu-die.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 10 loops waiting for it.
 */
#define KICK_READER_LOOPS 	10

/*
 * 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

/*
 * 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;

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.
 */
__DEFINE_URCU_TLS_GLOBAL(struct rcu_reader, rcu_reader);

#ifdef DEBUG_YIELD
unsigned int yield_active;
__DEFINE_URCU_TLS_GLOBAL(unsigned int, 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)
		urcu_die(ret);
#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	while ((ret = pthread_mutex_trylock(mutex)) != 0) {
		if (ret != EBUSY && ret != EINTR)
			urcu_die(ret);
		if (CMM_LOAD_SHARED(URCU_TLS(rcu_reader).need_mb)) {
			cmm_smp_mb();
			_CMM_STORE_SHARED(URCU_TLS(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)
		urcu_die(ret);
}

#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);
}

/*
 * Always called with rcu_registry lock held. Releases this lock between
 * iterations and grabs it again. Holds the lock when it returns.
 */
void update_counter_and_wait(void)
{
	CDS_LIST_HEAD(qsreaders);
	unsigned int wait_loops = 0;
	struct rcu_reader *index, *tmp;
#ifdef HAS_INCOHERENT_CACHES
	unsigned int wait_gp_loops = 0;
#endif /* HAS_INCOHERENT_CACHES */

	/* 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 URCU_TLS(rcu_reader).ctr count to become 0.
	 */
	for (;;) {
		if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
			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 {
			/* Temporarily unlock the registry lock. */
			mutex_unlock(&rcu_registry_lock);
			if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS)
				wait_gp();
			else
				caa_cpu_relax();
			/* Re-lock the registry lock before the next loop. */
			mutex_lock(&rcu_registry_lock);
		}
#else /* #ifndef HAS_INCOHERENT_CACHES */
		/*
		 * BUSY-LOOP. Force the reader thread to commit its
		 * URCU_TLS(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 {
			if (wait_gp_loops == KICK_READER_LOOPS) {
				smp_mb_master(RCU_MB_GROUP);
				wait_gp_loops = 0;
			}
			/* Temporarily unlock the registry lock. */
			mutex_unlock(&rcu_registry_lock);
			if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
				wait_gp();
				wait_gp_loops++;
			} else {
				caa_cpu_relax();
			}
			/* Re-lock the registry lock before the next loop. */
			mutex_lock(&rcu_registry_lock);
		}
#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);
	mutex_lock(&rcu_registry_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_registry_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() can release and grab again
	 * rcu_registry_lock interally.
	 */
	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
	 * 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();

	/*
	 * Wait for previous parity to be empty of readers.
	 * update_counter_and_wait() can release and grab again
	 * rcu_registry_lock interally.
	 */
	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_registry_lock because it
	 * iterates on reader threads.
	 */
	smp_mb_master(RCU_MB_GROUP);
out:
	mutex_unlock(&rcu_registry_lock);
	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)
{
	URCU_TLS(rcu_reader).tid = pthread_self();
	assert(URCU_TLS(rcu_reader).need_mb == 0);
	assert(!(URCU_TLS(rcu_reader).ctr & RCU_GP_CTR_NEST_MASK));

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

void rcu_unregister_thread(void)
{
	mutex_lock(&rcu_registry_lock);
	cds_list_del(&URCU_TLS(rcu_reader).node);
	mutex_unlock(&rcu_registry_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(URCU_TLS(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_registry_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)
		urcu_die(errno);
}

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

	ret = sigaction(SIGRCU, NULL, &act);
	if (ret)
		urcu_die(errno);
	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	#include "urcu/tls-compat.h"
	44
	45	#include "urcu-die.h"
	46
	47	/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
	48	#undef _LGPL_SOURCE
	49	#include "urcu.h"
	50	#define _LGPL_SOURCE
	51
	52	/*
	53	* If a reader is really non-cooperative and refuses to commit its
	54	* rcu_active_readers count to memory (there is no barrier in the reader
	55	* per-se), kick it after 10 loops waiting for it.
	56	*/
	57	#define KICK_READER_LOOPS 10
	58
	59	/*
	60	* Active attempts to check for reader Q.S. before calling futex().
	61	*/
	62	#define RCU_QS_ACTIVE_ATTEMPTS 100
	63
	64	#ifdef RCU_MEMBARRIER
	65	static int init_done;
	66	int has_sys_membarrier;
	67
	68	void __attribute__((constructor)) rcu_init(void);
	69	#endif
	70
	71	#ifdef RCU_MB
	72	void rcu_init(void)
	73	{
	74	}
	75	#endif
	76
	77	#ifdef RCU_SIGNAL
	78	static int init_done;
	79
	80	void __attribute__((constructor)) rcu_init(void);
	81	void __attribute__((destructor)) rcu_exit(void);
	82	#endif
	83
	84	/*
	85	* rcu_gp_lock ensures mutual exclusion between threads calling
	86	* synchronize_rcu().
	87	*/
	88	static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
	89	/*
	90	* rcu_registry_lock ensures mutual exclusion between threads
	91	* registering and unregistering themselves to/from the registry, and
	92	* with threads reading that registry from synchronize_rcu(). However,
	93	* this lock is not held all the way through the completion of awaiting
	94	* for the grace period. It is sporadically released between iterations
	95	* on the registry.
	96	* rcu_registry_lock may nest inside rcu_gp_lock.
	97	*/
	98	static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER;
	99
	100	int32_t gp_futex;
	101
	102	/*
	103	* Global grace period counter.
	104	* Contains the current RCU_GP_CTR_PHASE.
	105	* Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
	106	* Written to only by writer with mutex taken. Read by both writer and readers.
	107	*/
	108	unsigned long rcu_gp_ctr = RCU_GP_COUNT;
	109	/*
	110	* Written to only by each individual reader. Read by both the reader and the
	111	* writers.
	112	*/
	113	__DEFINE_URCU_TLS_GLOBAL(struct rcu_reader, rcu_reader);
	114
	115	#ifdef DEBUG_YIELD
	116	unsigned int yield_active;
	117	__DEFINE_URCU_TLS_GLOBAL(unsigned int, rand_yield);
	118	#endif
	119
	120	static CDS_LIST_HEAD(registry);
	121
	122	static void mutex_lock(pthread_mutex_t *mutex)
	123	{
	124	int ret;
	125
	126	#ifndef DISTRUST_SIGNALS_EXTREME
	127	ret = pthread_mutex_lock(mutex);
	128	if (ret)
	129	urcu_die(ret);
	130	#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	131	while ((ret = pthread_mutex_trylock(mutex)) != 0) {
	132	if (ret != EBUSY && ret != EINTR)
	133	urcu_die(ret);
	134	if (CMM_LOAD_SHARED(URCU_TLS(rcu_reader).need_mb)) {
	135	cmm_smp_mb();
	136	_CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
	137	cmm_smp_mb();
	138	}
	139	poll(NULL,0,10);
	140	}
	141	#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
	142	}
	143
	144	static void mutex_unlock(pthread_mutex_t *mutex)
	145	{
	146	int ret;
	147
	148	ret = pthread_mutex_unlock(mutex);
	149	if (ret)
	150	urcu_die(ret);
	151	}
	152
	153	#ifdef RCU_MEMBARRIER
	154	static void smp_mb_master(int group)
	155	{
	156	if (caa_likely(has_sys_membarrier))
	157	membarrier(MEMBARRIER_EXPEDITED);
	158	else
	159	cmm_smp_mb();
	160	}
	161	#endif
	162
	163	#ifdef RCU_MB
	164	static void smp_mb_master(int group)
	165	{
	166	cmm_smp_mb();
	167	}
	168	#endif
	169
	170	#ifdef RCU_SIGNAL
	171	static void force_mb_all_readers(void)
	172	{
	173	struct rcu_reader *index;
	174
	175	/*
	176	* Ask for each threads to execute a cmm_smp_mb() so we can consider the
	177	* compiler barriers around rcu read lock as real memory barriers.
	178	*/
	179	if (cds_list_empty(&registry))
	180	return;
	181	/*
	182	* pthread_kill has a cmm_smp_mb(). But beware, we assume it performs
	183	* a cache flush on architectures with non-coherent cache. Let's play
	184	* safe and don't assume anything : we use cmm_smp_mc() to make sure the
	185	* cache flush is enforced.
	186	*/
	187	cds_list_for_each_entry(index, &registry, node) {
	188	CMM_STORE_SHARED(index->need_mb, 1);
	189	pthread_kill(index->tid, SIGRCU);
	190	}
	191	/*
	192	* Wait for sighandler (and thus mb()) to execute on every thread.
	193	*
	194	* Note that the pthread_kill() will never be executed on systems
	195	* that correctly deliver signals in a timely manner. However, it
	196	* is not uncommon for kernels to have bugs that can result in
	197	* lost or unduly delayed signals.
	198	*
	199	* If you are seeing the below pthread_kill() executing much at
	200	* all, we suggest testing the underlying kernel and filing the
	201	* relevant bug report. For Linux kernels, we recommend getting
	202	* the Linux Test Project (LTP).
	203	*/
	204	cds_list_for_each_entry(index, &registry, node) {
	205	while (CMM_LOAD_SHARED(index->need_mb)) {
	206	pthread_kill(index->tid, SIGRCU);
	207	poll(NULL, 0, 1);
	208	}
	209	}
	210	cmm_smp_mb(); /* read ->need_mb before ending the barrier */
	211	}
	212
	213	static void smp_mb_master(int group)
	214	{
	215	force_mb_all_readers();
	216	}
	217	#endif /* #ifdef RCU_SIGNAL */
	218
	219	/*
	220	* synchronize_rcu() waiting. Single thread.
	221	*/
	222	static void wait_gp(void)
	223	{
	224	/* Read reader_gp before read futex */
	225	smp_mb_master(RCU_MB_GROUP);
	226	if (uatomic_read(&gp_futex) == -1)
	227	futex_async(&gp_futex, FUTEX_WAIT, -1,
	228	NULL, NULL, 0);
	229	}
	230
	231	/*
	232	* Always called with rcu_registry lock held. Releases this lock between
	233	* iterations and grabs it again. Holds the lock when it returns.
	234	*/
	235	void update_counter_and_wait(void)
	236	{
	237	CDS_LIST_HEAD(qsreaders);
	238	unsigned int wait_loops = 0;
	239	struct rcu_reader index, tmp;
	240	#ifdef HAS_INCOHERENT_CACHES
	241	unsigned int wait_gp_loops = 0;
	242	#endif /* HAS_INCOHERENT_CACHES */
	243
	244	/* Switch parity: 0 -> 1, 1 -> 0 */
	245	CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
	246
	247	/*
	248	* Must commit rcu_gp_ctr update to memory before waiting for quiescent
	249	* state. Failure to do so could result in the writer waiting forever
	250	* while new readers are always accessing data (no progress). Enforce
	251	* compiler-order of store to rcu_gp_ctr before load rcu_reader ctr.
	252	*/
	253	cmm_barrier();
	254
	255	/*
	256	*
	257	* Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	258	* model easier to understand. It does not have a big performance impact
	259	* anyway, given this is the write-side.
	260	*/
	261	cmm_smp_mb();
	262
	263	/*
	264	* Wait for each thread URCU_TLS(rcu_reader).ctr count to become 0.
	265	*/
	266	for (;;) {
	267	if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
	268	wait_loops++;
	269	if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
	270	uatomic_dec(&gp_futex);
	271	/* Write futex before read reader_gp */
	272	smp_mb_master(RCU_MB_GROUP);
	273	}
	274
	275	cds_list_for_each_entry_safe(index, tmp, &registry, node) {
	276	if (!rcu_gp_ongoing(&index->ctr))
	277	cds_list_move(&index->node, &qsreaders);
	278	}
	279
	280	#ifndef HAS_INCOHERENT_CACHES
	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	/* Temporarily unlock the registry lock. */
	290	mutex_unlock(&rcu_registry_lock);
	291	if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS)
	292	wait_gp();
	293	else
	294	caa_cpu_relax();
	295	/* Re-lock the registry lock before the next loop. */
	296	mutex_lock(&rcu_registry_lock);
	297	}
	298	#else /* #ifndef HAS_INCOHERENT_CACHES */
	299	/*
	300	* BUSY-LOOP. Force the reader thread to commit its
	301	* URCU_TLS(rcu_reader).ctr update to memory if we wait
	302	* for too long.
	303	*/
	304	if (cds_list_empty(&registry)) {
	305	if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
	306	/* Read reader_gp before write futex */
	307	smp_mb_master(RCU_MB_GROUP);
	308	uatomic_set(&gp_futex, 0);
	309	}
	310	break;
	311	} else {
	312	if (wait_gp_loops == KICK_READER_LOOPS) {
	313	smp_mb_master(RCU_MB_GROUP);
	314	wait_gp_loops = 0;
	315	}
	316	/* Temporarily unlock the registry lock. */
	317	mutex_unlock(&rcu_registry_lock);
	318	if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
	319	wait_gp();
	320	wait_gp_loops++;
	321	} else {
	322	caa_cpu_relax();
	323	}
	324	/* Re-lock the registry lock before the next loop. */
	325	mutex_lock(&rcu_registry_lock);
	326	}
	327	#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
	328	}
	329	/* put back the reader list in the registry */
	330	cds_list_splice(&qsreaders, &registry);
	331	}
	332
	333	void synchronize_rcu(void)
	334	{
	335	mutex_lock(&rcu_gp_lock);
	336	mutex_lock(&rcu_registry_lock);
	337
	338	if (cds_list_empty(&registry))
	339	goto out;
	340
	341	/*
	342	* All threads should read qparity before accessing data structure
	343	* where new ptr points to. Must be done within rcu_registry_lock
	344	* because it iterates on reader threads.
	345	*/
	346	/* Write new ptr before changing the qparity */
	347	smp_mb_master(RCU_MB_GROUP);
	348
	349	/*
	350	* Wait for previous parity to be empty of readers.
	351	* update_counter_and_wait() can release and grab again
	352	* rcu_registry_lock interally.
	353	*/
	354	update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */
	355
	356	/*
	357	* Must finish waiting for quiescent state for parity 0 before
	358	* committing next rcu_gp_ctr update to memory. Failure to do so could
	359	* result in the writer waiting forever while new readers are always
	360	* accessing data (no progress). Enforce compiler-order of load
	361	* URCU_TLS(rcu_reader).ctr before store to rcu_gp_ctr.
	362	*/
	363	cmm_barrier();
	364
	365	/*
	366	* Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	367	* model easier to understand. It does not have a big performance impact
	368	* anyway, given this is the write-side.
	369	*/
	370	cmm_smp_mb();
	371
	372	/*
	373	* Wait for previous parity to be empty of readers.
	374	* update_counter_and_wait() can release and grab again
	375	* rcu_registry_lock interally.
	376	*/
	377	update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */
	378
	379	/*
	380	* Finish waiting for reader threads before letting the old ptr
	381	* being freed. Must be done within rcu_registry_lock because it
	382	* iterates on reader threads.
	383	*/
	384	smp_mb_master(RCU_MB_GROUP);
	385	out:
	386	mutex_unlock(&rcu_registry_lock);
	387	mutex_unlock(&rcu_gp_lock);
	388	}
	389
	390	/*
	391	* library wrappers to be used by non-LGPL compatible source code.
	392	*/
	393
	394	void rcu_read_lock(void)
	395	{
	396	_rcu_read_lock();
	397	}
	398
	399	void rcu_read_unlock(void)
	400	{
	401	_rcu_read_unlock();
	402	}
	403
	404	void rcu_register_thread(void)
	405	{
	406	URCU_TLS(rcu_reader).tid = pthread_self();
	407	assert(URCU_TLS(rcu_reader).need_mb == 0);
	408	assert(!(URCU_TLS(rcu_reader).ctr & RCU_GP_CTR_NEST_MASK));
	409
	410	mutex_lock(&rcu_registry_lock);
	411	rcu_init(); /* In case gcc does not support constructor attribute */
	412	cds_list_add(&URCU_TLS(rcu_reader).node, &registry);
	413	mutex_unlock(&rcu_registry_lock);
	414	}
	415
	416	void rcu_unregister_thread(void)
	417	{
	418	mutex_lock(&rcu_registry_lock);
	419	cds_list_del(&URCU_TLS(rcu_reader).node);
	420	mutex_unlock(&rcu_registry_lock);
	421	}
	422
	423	#ifdef RCU_MEMBARRIER
	424	void rcu_init(void)
	425	{
	426	if (init_done)
	427	return;
	428	init_done = 1;
	429	if (!membarrier(MEMBARRIER_EXPEDITED \| MEMBARRIER_QUERY))
	430	has_sys_membarrier = 1;
	431	}
	432	#endif
	433
	434	#ifdef RCU_SIGNAL
	435	static void sigrcu_handler(int signo, siginfo_t siginfo, void context)
	436	{
	437	/*
	438	* Executing this cmm_smp_mb() is the only purpose of this signal handler.
	439	* It punctually promotes cmm_barrier() into cmm_smp_mb() on every thread it is
	440	* executed on.
	441	*/
	442	cmm_smp_mb();
	443	_CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
	444	cmm_smp_mb();
	445	}
	446
	447	/*
	448	* rcu_init constructor. Called when the library is linked, but also when
	449	* reader threads are calling rcu_register_thread().
	450	* Should only be called by a single thread at a given time. This is ensured by
	451	* holing the rcu_registry_lock from rcu_register_thread() or by running
	452	* at library load time, which should not be executed by multiple
	453	* threads nor concurrently with rcu_register_thread() anyway.
	454	*/
	455	void rcu_init(void)
	456	{
	457	struct sigaction act;
	458	int ret;
	459
	460	if (init_done)
	461	return;
	462	init_done = 1;
	463
	464	act.sa_sigaction = sigrcu_handler;
	465	act.sa_flags = SA_SIGINFO \| SA_RESTART;
	466	sigemptyset(&act.sa_mask);
	467	ret = sigaction(SIGRCU, &act, NULL);
	468	if (ret)
	469	urcu_die(errno);
	470	}
	471
	472	void rcu_exit(void)
	473	{
	474	struct sigaction act;
	475	int ret;
	476
	477	ret = sigaction(SIGRCU, NULL, &act);
	478	if (ret)
	479	urcu_die(errno);
	480	assert(act.sa_sigaction == sigrcu_handler);
	481	assert(cds_list_empty(&registry));
	482	}
	483
	484	#endif /* #ifdef RCU_SIGNAL */
	485
	486	DEFINE_RCU_FLAVOR(rcu_flavor);
	487
	488	#include "urcu-call-rcu-impl.h"
	489	#include "urcu-defer-impl.h"