[urcu.git] / urcu-bp.c

/*
 * urcu-bp.c
 *
 * Userspace RCU library, "bulletproof" version.
 *
 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 *
 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
 */

#define _GNU_SOURCE
#define _LGPL_SOURCE
#include <stdio.h>
#include <pthread.h>
#include <signal.h>
#include <assert.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <poll.h>
#include <unistd.h>
#include <sys/mman.h>

#include "urcu/wfcqueue.h"
#include "urcu/map/urcu-bp.h"
#include "urcu/static/urcu-bp.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-bp.h"
#define _LGPL_SOURCE

#ifndef MAP_ANONYMOUS
#define MAP_ANONYMOUS MAP_ANON
#endif

#ifdef __linux__
static
void *mremap_wrapper(void *old_address, size_t old_size,
		size_t new_size, int flags)
{
	return mremap(old_address, old_size, new_size, flags);
}
#else

#define MREMAP_MAYMOVE	1
#define MREMAP_FIXED	2

/*
 * mremap wrapper for non-Linux systems. Maps a RW, anonymous private mapping.
 * This is not generic.
*/
static
void *mremap_wrapper(void *old_address, size_t old_size,
		size_t new_size, int flags)
{
	void *new_address;

	assert(flags & MREMAP_MAYMOVE);
	assert(!(flags & MREMAP_FIXED));
	new_address = mmap(old_address, new_size,
			   PROT_READ | PROT_WRITE,
			   MAP_ANONYMOUS | MAP_PRIVATE,
			   -1, 0);
	if (new_address == MAP_FAILED)
		return MAP_FAILED;
	if (old_address) {
		memcpy(new_address, old_address, old_size);
		munmap(old_address, old_size);
	}
	return new_address;
}
#endif

/* Sleep delay in us */
#define RCU_SLEEP_DELAY		1000
#define ARENA_INIT_ALLOC	16

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

void __attribute__((destructor)) rcu_bp_exit(void);

static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;

#ifdef DEBUG_YIELD
unsigned int rcu_yield_active;
DEFINE_URCU_TLS(unsigned int, rcu_rand_yield);
#endif

/*
 * 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;

/*
 * Pointer to registry elements. Written to only by each individual reader. Read
 * by both the reader and the writers.
 */
DEFINE_URCU_TLS(struct rcu_reader *, rcu_reader);

static CDS_LIST_HEAD(registry);

struct registry_arena {
	void *p;
	size_t len;
	size_t used;
};

static struct registry_arena registry_arena;

/* Saved fork signal mask, protected by rcu_gp_lock */
static sigset_t saved_fork_signal_mask;

static void rcu_gc_registry(void);

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

#ifndef DISTRUST_SIGNALS_EXTREME
	ret = pthread_mutex_lock(mutex);
	if (ret)
		urcu_die(ret);
#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	while ((ret = pthread_mutex_trylock(mutex)) != 0) {
		if (ret != EBUSY && ret != EINTR)
			urcu_die(ret);
		poll(NULL,0,10);
	}
#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
}

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

	ret = pthread_mutex_unlock(mutex);
	if (ret)
		urcu_die(ret);
}

static void wait_for_readers(struct cds_list_head *input_readers,
			struct cds_list_head *cur_snap_readers,
			struct cds_list_head *qsreaders)
{
	int wait_loops = 0;
	struct rcu_reader *index, *tmp;

	/*
	 * Wait for each thread URCU_TLS(rcu_reader).ctr to either
	 * indicate quiescence (not nested), or observe the current
	 * rcu_gp_ctr value.
	 */
	for (;;) {
		wait_loops++;
		cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
			switch (rcu_reader_state(&index->ctr)) {
			case RCU_READER_ACTIVE_CURRENT:
				if (cur_snap_readers) {
					cds_list_move(&index->node,
						cur_snap_readers);
					break;
				}
				/* Fall-through */
			case RCU_READER_INACTIVE:
				cds_list_move(&index->node, qsreaders);
				break;
			case RCU_READER_ACTIVE_OLD:
				/*
				 * Old snapshot. Leaving node in
				 * input_readers will make us busy-loop
				 * until the snapshot becomes current or
				 * the reader becomes inactive.
				 */
				break;
			}
		}

		if (cds_list_empty(input_readers)) {
			break;
		} else {
			if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
				usleep(RCU_SLEEP_DELAY);
			else
				caa_cpu_relax();
		}
	}
}

void synchronize_rcu(void)
{
	CDS_LIST_HEAD(cur_snap_readers);
	CDS_LIST_HEAD(qsreaders);
	sigset_t newmask, oldmask;
	int ret;

	ret = sigemptyset(&newmask);
	assert(!ret);
	ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
	assert(!ret);

	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. */
	/* Write new ptr before changing the qparity */
	cmm_smp_mb();

	/* Remove old registry elements */
	rcu_gc_registry();

	/*
	 * Wait for readers to observe original parity or be quiescent.
	 */
	wait_for_readers(&registry, &cur_snap_readers, &qsreaders);

	/*
	 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	 * model easier to understand. It does not have a big performance impact
	 * anyway, given this is the write-side.
	 */
	cmm_smp_mb();

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

	/*
	 * Must commit qparity update to memory before waiting for other parity
	 * quiescent state. Failure to do so could result in the writer waiting
	 * forever while new readers are always accessing data (no progress).
	 * Ensured by CMM_STORE_SHARED and CMM_LOAD_SHARED.
	 */

	/*
	 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	 * model easier to understand. It does not have a big performance impact
	 * anyway, given this is the write-side.
	 */
	cmm_smp_mb();

	/*
	 * Wait for readers to observe new parity or be quiescent.
	 */
	wait_for_readers(&cur_snap_readers, NULL, &qsreaders);

	/*
	 * Put quiescent reader list back into registry.
	 */
	cds_list_splice(&qsreaders, &registry);

	/*
	 * Finish waiting for reader threads before letting the old ptr being
	 * freed.
	 */
	cmm_smp_mb();
out:
	mutex_unlock(&rcu_gp_lock);
	ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
	assert(!ret);
}

/*
 * 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();
}

/*
 * only grow for now.
 */
static void resize_arena(struct registry_arena *arena, size_t len)
{
	void *new_arena;

	if (!arena->p)
		new_arena = mmap(arena->p, len,
				 PROT_READ | PROT_WRITE,
				 MAP_ANONYMOUS | MAP_PRIVATE,
				 -1, 0);
	else
		new_arena = mremap_wrapper(arena->p, arena->len,
				   	len, MREMAP_MAYMOVE);
	assert(new_arena != MAP_FAILED);

	/*
	 * re-used the same region ?
	 */
	if (new_arena == arena->p)
		return;

	bzero(new_arena + arena->len, len - arena->len);
	arena->p = new_arena;
}

/* Called with signals off and mutex locked */
static void add_thread(void)
{
	struct rcu_reader *rcu_reader_reg;

	if (registry_arena.len
	    < registry_arena.used + sizeof(struct rcu_reader))
		resize_arena(&registry_arena,
		caa_max(registry_arena.len << 1, ARENA_INIT_ALLOC));
	/*
	 * Find a free spot.
	 */
	for (rcu_reader_reg = registry_arena.p;
	     (void *)rcu_reader_reg < registry_arena.p + registry_arena.len;
	     rcu_reader_reg++) {
		if (!rcu_reader_reg->alloc)
			break;
	}
	rcu_reader_reg->alloc = 1;
	registry_arena.used += sizeof(struct rcu_reader);

	/* Add to registry */
	rcu_reader_reg->tid = pthread_self();
	assert(rcu_reader_reg->ctr == 0);
	cds_list_add(&rcu_reader_reg->node, &registry);
	URCU_TLS(rcu_reader) = rcu_reader_reg;
}

/* Called with signals off and mutex locked */
static void rcu_gc_registry(void)
{
	struct rcu_reader *rcu_reader_reg;
	pthread_t tid;
	int ret;

	for (rcu_reader_reg = registry_arena.p;
	     (void *)rcu_reader_reg < registry_arena.p + registry_arena.len;
	     rcu_reader_reg++) {
		if (!rcu_reader_reg->alloc)
			continue;
		tid = rcu_reader_reg->tid;
		ret = pthread_kill(tid, 0);
		assert(ret != EINVAL);
		if (ret == ESRCH) {
			cds_list_del(&rcu_reader_reg->node);
			rcu_reader_reg->ctr = 0;
			rcu_reader_reg->alloc = 0;
			registry_arena.used -= sizeof(struct rcu_reader);
		}
	}
}

/* Disable signals, take mutex, add to registry */
void rcu_bp_register(void)
{
	sigset_t newmask, oldmask;
	int ret;

	ret = sigemptyset(&newmask);
	assert(!ret);
	ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
	assert(!ret);

	/*
	 * Check if a signal concurrently registered our thread since
	 * the check in rcu_read_lock(). */
	if (URCU_TLS(rcu_reader))
		goto end;

	mutex_lock(&rcu_gp_lock);
	add_thread();
	mutex_unlock(&rcu_gp_lock);
end:
	ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
	assert(!ret);
}

void rcu_bp_exit(void)
{
	if (registry_arena.p)
		munmap(registry_arena.p, registry_arena.len);
}

/*
 * Holding the rcu_gp_lock across fork will make sure we fork() don't race with
 * a concurrent thread executing with this same lock held. This ensures that the
 * registry is in a coherent state in the child.
 */
void rcu_bp_before_fork(void)
{
	sigset_t newmask, oldmask;
	int ret;

	ret = sigemptyset(&newmask);
	assert(!ret);
	ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
	assert(!ret);
	mutex_lock(&rcu_gp_lock);
	saved_fork_signal_mask = oldmask;
}

void rcu_bp_after_fork_parent(void)
{
	sigset_t oldmask;
	int ret;

	oldmask = saved_fork_signal_mask;
	mutex_unlock(&rcu_gp_lock);
	ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
	assert(!ret);
}

void rcu_bp_after_fork_child(void)
{
	sigset_t oldmask;
	int ret;

	rcu_gc_registry();
	oldmask = saved_fork_signal_mask;
	mutex_unlock(&rcu_gp_lock);
	ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
	assert(!ret);
}

void *rcu_dereference_sym_bp(void *p)
{
	return _rcu_dereference(p);
}

void *rcu_set_pointer_sym_bp(void **p, void *v)
{
	cmm_wmb();
	uatomic_set(p, v);
	return v;
}

void *rcu_xchg_pointer_sym_bp(void **p, void *v)
{
	cmm_wmb();
	return uatomic_xchg(p, v);
}

void *rcu_cmpxchg_pointer_sym_bp(void **p, void *old, void *_new)
{
	cmm_wmb();
	return uatomic_cmpxchg(p, old, _new);
}

DEFINE_RCU_FLAVOR(rcu_flavor);

#include "urcu-call-rcu-impl.h"
#include "urcu-defer-impl.h"
Commit	Line	Data
fdee2e6d MD	1	/*
	2	* urcu-bp.c
	3	*
	4	* Userspace RCU library, "bulletproof" version.
	5	*
6982d6d7	6	* Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
fdee2e6d MD	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
0617bf4c	26	#define _GNU_SOURCE
71c811bf	27	#define _LGPL_SOURCE
fdee2e6d MD	28	#include <stdio.h>
	29	#include <pthread.h>
	30	#include <signal.h>
	31	#include <assert.h>
	32	#include <stdlib.h>
	33	#include <string.h>
	34	#include <errno.h>
	35	#include <poll.h>
	36	#include <unistd.h>
	37	#include <sys/mman.h>
	38
d73fb81f	39	#include "urcu/wfcqueue.h"
57760d44	40	#include "urcu/map/urcu-bp.h"
af7c2dbe	41	#include "urcu/static/urcu-bp.h"
618b2595	42	#include "urcu-pointer.h"
bd252a04	43	#include "urcu/tls-compat.h"
71c811bf	44
4a6d7378 MD	45	#include "urcu-die.h"
4a6d7378 MD	46
fdee2e6d	47	/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
71c811bf	48	#undef _LGPL_SOURCE
fdee2e6d	49	#include "urcu-bp.h"
71c811bf	50	#define _LGPL_SOURCE
fdee2e6d	51
4c1ae2ea MD	52	#ifndef MAP_ANONYMOUS
	53	#define MAP_ANONYMOUS MAP_ANON
	54	#endif
	55
c7eaf61c MD	56	#ifdef __linux__
	57	static
	58	void mremap_wrapper(void old_address, size_t old_size,
	59	size_t new_size, int flags)
	60	{
	61	return mremap(old_address, old_size, new_size, flags);
	62	}
	63	#else
45a4872f MD	64
	65	#define MREMAP_MAYMOVE 1
	66	#define MREMAP_FIXED 2
	67
	68	/*
	69	* mremap wrapper for non-Linux systems. Maps a RW, anonymous private mapping.
	70	* This is not generic.
	71	*/
c7eaf61c MD	72	static
	73	void mremap_wrapper(void old_address, size_t old_size,
	74	size_t new_size, int flags)
45a4872f	75	{
dc745ef6	76	void *new_address;
45a4872f MD	77
	78	assert(flags & MREMAP_MAYMOVE);
	79	assert(!(flags & MREMAP_FIXED));
	80	new_address = mmap(old_address, new_size,
	81	PROT_READ \| PROT_WRITE,
	82	MAP_ANONYMOUS \| MAP_PRIVATE,
	83	-1, 0);
	84	if (new_address == MAP_FAILED)
	85	return MAP_FAILED;
	86	if (old_address) {
	87	memcpy(new_address, old_address, old_size);
	88	munmap(old_address, old_size);
	89	}
	90	return new_address;
	91	}
	92	#endif
	93
fdee2e6d MD	94	/* Sleep delay in us */
	95	#define RCU_SLEEP_DELAY 1000
	96	#define ARENA_INIT_ALLOC 16
	97
b7b6a8f5 PB	98	/*
	99	* Active attempts to check for reader Q.S. before calling sleep().
	100	*/
	101	#define RCU_QS_ACTIVE_ATTEMPTS 100
	102
02be5561	103	void __attribute__((destructor)) rcu_bp_exit(void);
fdee2e6d	104
6abb4bd5	105	static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
fdee2e6d MD	106
fdee2e6d MD	107	#ifdef DEBUG_YIELD
1de4df4b MD	108	unsigned int rcu_yield_active;
1de4df4b MD	109	DEFINE_URCU_TLS(unsigned int, rcu_rand_yield);
fdee2e6d MD	110	#endif
	111
	112	/*
	113	* Global grace period counter.
02be5561	114	* Contains the current RCU_GP_CTR_PHASE.
fdee2e6d MD	115	* Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
	116	* Written to only by writer with mutex taken. Read by both writer and readers.
	117	*/
52c75091	118	unsigned long rcu_gp_ctr = RCU_GP_COUNT;
fdee2e6d MD	119
	120	/*
	121	* Pointer to registry elements. Written to only by each individual reader. Read
	122	* by both the reader and the writers.
	123	*/
bd252a04	124	DEFINE_URCU_TLS(struct rcu_reader *, rcu_reader);
fdee2e6d	125
16aa9ee8	126	static CDS_LIST_HEAD(registry);
fdee2e6d MD	127
	128	struct registry_arena {
	129	void *p;
	130	size_t len;
	131	size_t used;
	132	};
	133
	134	static struct registry_arena registry_arena;
	135
4cf1675f MD	136	/* Saved fork signal mask, protected by rcu_gp_lock */
	137	static sigset_t saved_fork_signal_mask;
	138
fdee2e6d MD	139	static void rcu_gc_registry(void);
fdee2e6d MD	140
6abb4bd5	141	static void mutex_lock(pthread_mutex_t *mutex)
fdee2e6d MD	142	{
	143	int ret;
	144
	145	#ifndef DISTRUST_SIGNALS_EXTREME
6abb4bd5	146	ret = pthread_mutex_lock(mutex);
4a6d7378 MD	147	if (ret)
4a6d7378 MD	148	urcu_die(ret);
fdee2e6d	149	#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
6abb4bd5	150	while ((ret = pthread_mutex_trylock(mutex)) != 0) {
4a6d7378 MD	151	if (ret != EBUSY && ret != EINTR)
4a6d7378 MD	152	urcu_die(ret);
fdee2e6d MD	153	poll(NULL,0,10);
	154	}
	155	#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
	156	}
	157
6abb4bd5	158	static void mutex_unlock(pthread_mutex_t *mutex)
fdee2e6d MD	159	{
	160	int ret;
	161
6abb4bd5	162	ret = pthread_mutex_unlock(mutex);
4a6d7378 MD	163	if (ret)
4a6d7378 MD	164	urcu_die(ret);
fdee2e6d MD	165	}
fdee2e6d MD	166
52c75091 MD	167	static void wait_for_readers(struct cds_list_head *input_readers,
	168	struct cds_list_head *cur_snap_readers,
	169	struct cds_list_head *qsreaders)
fdee2e6d	170	{
fdee2e6d	171	int wait_loops = 0;
02be5561	172	struct rcu_reader index, tmp;
fdee2e6d	173
fdee2e6d	174	/*
dd61d077 MD	175	* Wait for each thread URCU_TLS(rcu_reader).ctr to either
	176	* indicate quiescence (not nested), or observe the current
	177	* rcu_gp_ctr value.
fdee2e6d MD	178	*/
	179	for (;;) {
	180	wait_loops++;
52c75091 MD	181	cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
	182	switch (rcu_reader_state(&index->ctr)) {
	183	case RCU_READER_ACTIVE_CURRENT:
	184	if (cur_snap_readers) {
	185	cds_list_move(&index->node,
	186	cur_snap_readers);
	187	break;
	188	}
	189	/* Fall-through */
	190	case RCU_READER_INACTIVE:
	191	cds_list_move(&index->node, qsreaders);
	192	break;
	193	case RCU_READER_ACTIVE_OLD:
	194	/*
	195	* Old snapshot. Leaving node in
	196	* input_readers will make us busy-loop
	197	* until the snapshot becomes current or
	198	* the reader becomes inactive.
	199	*/
	200	break;
	201	}
fdee2e6d MD	202	}
fdee2e6d MD	203
52c75091	204	if (cds_list_empty(input_readers)) {
fdee2e6d MD	205	break;
	206	} else {
	207	if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
	208	usleep(RCU_SLEEP_DELAY);
	209	else
06f22bdb	210	caa_cpu_relax();
fdee2e6d MD	211	}
fdee2e6d MD	212	}
fdee2e6d MD	213	}
	214
	215	void synchronize_rcu(void)
	216	{
52c75091 MD	217	CDS_LIST_HEAD(cur_snap_readers);
52c75091 MD	218	CDS_LIST_HEAD(qsreaders);
fdee2e6d MD	219	sigset_t newmask, oldmask;
	220	int ret;
	221
	222	ret = sigemptyset(&newmask);
	223	assert(!ret);
	224	ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
	225	assert(!ret);
	226
6abb4bd5	227	mutex_lock(&rcu_gp_lock);
fdee2e6d	228
16aa9ee8	229	if (cds_list_empty(&registry))
2dfb8b5e	230	goto out;
fdee2e6d MD	231
fdee2e6d MD	232	/* All threads should read qparity before accessing data structure
2dfb8b5e	233	* where new ptr points to. */
fdee2e6d	234	/* Write new ptr before changing the qparity */
5481ddb3	235	cmm_smp_mb();
fdee2e6d	236
2dfb8b5e MD	237	/* Remove old registry elements */
2dfb8b5e MD	238	rcu_gc_registry();
fdee2e6d MD	239
fdee2e6d MD	240	/*
dd61d077 MD	241	* Wait for readers to observe original parity or be quiescent.
dd61d077 MD	242	*/
52c75091	243	wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
dd61d077 MD	244
	245	/*
	246	* Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	247	* model easier to understand. It does not have a big performance impact
	248	* anyway, given this is the write-side.
	249	*/
	250	cmm_smp_mb();
	251
	252	/* Switch parity: 0 -> 1, 1 -> 0 */
	253	CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
	254
	255	/*
	256	* Must commit qparity update to memory before waiting for other parity
	257	* quiescent state. Failure to do so could result in the writer waiting
	258	* forever while new readers are always accessing data (no progress).
	259	* Ensured by CMM_STORE_SHARED and CMM_LOAD_SHARED.
fdee2e6d	260	*/
fdee2e6d MD	261
fdee2e6d MD	262	/*
5481ddb3	263	* Adding a cmm_smp_mb() which is _not_ formally required, but makes the
fdee2e6d MD	264	* model easier to understand. It does not have a big performance impact
	265	* anyway, given this is the write-side.
	266	*/
5481ddb3	267	cmm_smp_mb();
fdee2e6d	268
fdee2e6d	269	/*
dd61d077	270	* Wait for readers to observe new parity or be quiescent.
fdee2e6d	271	*/
52c75091 MD	272	wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
	273
	274	/*
	275	* Put quiescent reader list back into registry.
	276	*/
	277	cds_list_splice(&qsreaders, &registry);
fdee2e6d MD	278
fdee2e6d MD	279	/*
2dfb8b5e MD	280	* Finish waiting for reader threads before letting the old ptr being
2dfb8b5e MD	281	* freed.
fdee2e6d	282	*/
5481ddb3	283	cmm_smp_mb();
2dfb8b5e	284	out:
6abb4bd5	285	mutex_unlock(&rcu_gp_lock);
fdee2e6d MD	286	ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
	287	assert(!ret);
	288	}
	289
	290	/*
	291	* library wrappers to be used by non-LGPL compatible source code.
	292	*/
	293
	294	void rcu_read_lock(void)
	295	{
	296	_rcu_read_lock();
	297	}
	298
	299	void rcu_read_unlock(void)
	300	{
	301	_rcu_read_unlock();
	302	}
	303
	304	/*
	305	* only grow for now.
	306	*/
	307	static void resize_arena(struct registry_arena *arena, size_t len)
	308	{
	309	void *new_arena;
	310
0617bf4c MD	311	if (!arena->p)
	312	new_arena = mmap(arena->p, len,
	313	PROT_READ \| PROT_WRITE,
	314	MAP_ANONYMOUS \| MAP_PRIVATE,
	315	-1, 0);
	316	else
c7eaf61c MD	317	new_arena = mremap_wrapper(arena->p, arena->len,
c7eaf61c MD	318	len, MREMAP_MAYMOVE);
0617bf4c MD	319	assert(new_arena != MAP_FAILED);
0617bf4c MD	320
fdee2e6d MD	321	/*
	322	* re-used the same region ?
	323	*/
	324	if (new_arena == arena->p)
	325	return;
	326
fdee2e6d MD	327	bzero(new_arena + arena->len, len - arena->len);
	328	arena->p = new_arena;
	329	}
	330
	331	/* Called with signals off and mutex locked */
	332	static void add_thread(void)
	333	{
02be5561	334	struct rcu_reader *rcu_reader_reg;
fdee2e6d MD	335
fdee2e6d MD	336	if (registry_arena.len
02be5561	337	< registry_arena.used + sizeof(struct rcu_reader))
fdee2e6d	338	resize_arena(&registry_arena,
2f8a5ae7	339	caa_max(registry_arena.len << 1, ARENA_INIT_ALLOC));
fdee2e6d MD	340	/*
	341	* Find a free spot.
	342	*/
02be5561 MD	343	for (rcu_reader_reg = registry_arena.p;
	344	(void *)rcu_reader_reg < registry_arena.p + registry_arena.len;
	345	rcu_reader_reg++) {
	346	if (!rcu_reader_reg->alloc)
fdee2e6d MD	347	break;
fdee2e6d MD	348	}
02be5561 MD	349	rcu_reader_reg->alloc = 1;
02be5561 MD	350	registry_arena.used += sizeof(struct rcu_reader);
fdee2e6d MD	351
fdee2e6d MD	352	/* Add to registry */
02be5561 MD	353	rcu_reader_reg->tid = pthread_self();
02be5561 MD	354	assert(rcu_reader_reg->ctr == 0);
16aa9ee8	355	cds_list_add(&rcu_reader_reg->node, &registry);
bd252a04	356	URCU_TLS(rcu_reader) = rcu_reader_reg;
fdee2e6d MD	357	}
	358
	359	/* Called with signals off and mutex locked */
	360	static void rcu_gc_registry(void)
	361	{
02be5561	362	struct rcu_reader *rcu_reader_reg;
fdee2e6d MD	363	pthread_t tid;
	364	int ret;
	365
02be5561 MD	366	for (rcu_reader_reg = registry_arena.p;
	367	(void *)rcu_reader_reg < registry_arena.p + registry_arena.len;
	368	rcu_reader_reg++) {
	369	if (!rcu_reader_reg->alloc)
fdee2e6d	370	continue;
02be5561	371	tid = rcu_reader_reg->tid;
fdee2e6d MD	372	ret = pthread_kill(tid, 0);
	373	assert(ret != EINVAL);
	374	if (ret == ESRCH) {
16aa9ee8	375	cds_list_del(&rcu_reader_reg->node);
79266051	376	rcu_reader_reg->ctr = 0;
02be5561 MD	377	rcu_reader_reg->alloc = 0;
02be5561 MD	378	registry_arena.used -= sizeof(struct rcu_reader);
fdee2e6d MD	379	}
	380	}
	381	}
	382
	383	/* Disable signals, take mutex, add to registry */
	384	void rcu_bp_register(void)
	385	{
	386	sigset_t newmask, oldmask;
	387	int ret;
	388
	389	ret = sigemptyset(&newmask);
	390	assert(!ret);
	391	ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
	392	assert(!ret);
	393
	394	/*
	395	* Check if a signal concurrently registered our thread since
	396	* the check in rcu_read_lock(). */
bd252a04	397	if (URCU_TLS(rcu_reader))
fdee2e6d MD	398	goto end;
fdee2e6d MD	399
6abb4bd5	400	mutex_lock(&rcu_gp_lock);
fdee2e6d	401	add_thread();
6abb4bd5	402	mutex_unlock(&rcu_gp_lock);
fdee2e6d MD	403	end:
	404	ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
	405	assert(!ret);
	406	}
	407
9380711a	408	void rcu_bp_exit(void)
fdee2e6d	409	{
9380711a MD	410	if (registry_arena.p)
9380711a MD	411	munmap(registry_arena.p, registry_arena.len);
fdee2e6d	412	}
4cf1675f MD	413
	414	/*
	415	* Holding the rcu_gp_lock across fork will make sure we fork() don't race with
	416	* a concurrent thread executing with this same lock held. This ensures that the
	417	* registry is in a coherent state in the child.
	418	*/
	419	void rcu_bp_before_fork(void)
	420	{
	421	sigset_t newmask, oldmask;
	422	int ret;
	423
	424	ret = sigemptyset(&newmask);
	425	assert(!ret);
	426	ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
	427	assert(!ret);
	428	mutex_lock(&rcu_gp_lock);
	429	saved_fork_signal_mask = oldmask;
	430	}
	431
	432	void rcu_bp_after_fork_parent(void)
	433	{
	434	sigset_t oldmask;
	435	int ret;
	436
	437	oldmask = saved_fork_signal_mask;
	438	mutex_unlock(&rcu_gp_lock);
	439	ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
	440	assert(!ret);
	441	}
	442
	443	void rcu_bp_after_fork_child(void)
	444	{
	445	sigset_t oldmask;
	446	int ret;
	447
	448	rcu_gc_registry();
	449	oldmask = saved_fork_signal_mask;
	450	mutex_unlock(&rcu_gp_lock);
	451	ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
	452	assert(!ret);
	453	}
5e77fc1f	454
9b7981bb MD	455	void rcu_dereference_sym_bp(void p)
	456	{
	457	return _rcu_dereference(p);
	458	}
	459
5efd3cd2 MD	460	void rcu_set_pointer_sym_bp(void p, void v)
	461	{
	462	cmm_wmb();
424d4ed5 MD	463	uatomic_set(p, v);
424d4ed5 MD	464	return v;
5efd3cd2 MD	465	}
	466
	467	void rcu_xchg_pointer_sym_bp(void p, void v)
	468	{
	469	cmm_wmb();
	470	return uatomic_xchg(p, v);
	471	}
	472
	473	void rcu_cmpxchg_pointer_sym_bp(void p, void old, void *_new)
	474	{
	475	cmm_wmb();
	476	return uatomic_cmpxchg(p, old, _new);
	477	}
	478
5e6b23a6	479	DEFINE_RCU_FLAVOR(rcu_flavor);
541d828d	480
5e77fc1f	481	#include "urcu-call-rcu-impl.h"
0376e7b2	482	#include "urcu-defer-impl.h"