[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

struct rcu_gp 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 = sigfillset(&newmask);
	assert(!ret);
	ret = pthread_sigmask(SIG_BLOCK, &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();
}

int rcu_read_ongoing(void)
{
	return _rcu_read_ongoing();
}

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

	old_len = arena->len;

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

	/*
	 * Zero the newly allocated memory. Since mmap() does not
	 * clearly specify if memory is zeroed or not (although it is
	 * very likely that it is), be extra careful by not expecting
	 * the new range to be zeroed by mremap.
	 */
	bzero(new_p + old_len, len - old_len);

	/*
	 * If we did not re-use the same region, we need to update the
	 * arena pointer.
	 */
	if (new_p != arena->p)
		arena->p = new_p;

	arena->len = len;
}

/* 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 = sigfillset(&newmask);
	assert(!ret);
	ret = pthread_sigmask(SIG_BLOCK, &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 = sigfillset(&newmask);
	assert(!ret);
	ret = pthread_sigmask(SIG_BLOCK, &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
	1	/*
	2	* urcu-bp.c
	3	*
	4	* Userspace RCU library, "bulletproof" version.
	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 _GNU_SOURCE
	27	#define _LGPL_SOURCE
	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
	39	#include "urcu/wfcqueue.h"
	40	#include "urcu/map/urcu-bp.h"
	41	#include "urcu/static/urcu-bp.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-bp.h"
	50	#define _LGPL_SOURCE
	51
	52	#ifndef MAP_ANONYMOUS
	53	#define MAP_ANONYMOUS MAP_ANON
	54	#endif
	55
	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
	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	*/
	72	static
	73	void mremap_wrapper(void old_address, size_t old_size,
	74	size_t new_size, int flags)
	75	{
	76	void *new_address;
	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
	94	/* Sleep delay in us */
	95	#define RCU_SLEEP_DELAY 1000
	96	#define ARENA_INIT_ALLOC 16
	97
	98	/*
	99	* Active attempts to check for reader Q.S. before calling sleep().
	100	*/
	101	#define RCU_QS_ACTIVE_ATTEMPTS 100
	102
	103	void __attribute__((destructor)) rcu_bp_exit(void);
	104
	105	static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
	106
	107	#ifdef DEBUG_YIELD
	108	unsigned int rcu_yield_active;
	109	DEFINE_URCU_TLS(unsigned int, rcu_rand_yield);
	110	#endif
	111
	112	struct rcu_gp rcu_gp = { .ctr = RCU_GP_COUNT };
	113
	114	/*
	115	* Pointer to registry elements. Written to only by each individual reader. Read
	116	* by both the reader and the writers.
	117	*/
	118	DEFINE_URCU_TLS(struct rcu_reader *, rcu_reader);
	119
	120	static CDS_LIST_HEAD(registry);
	121
	122	struct registry_arena {
	123	void *p;
	124	size_t len;
	125	size_t used;
	126	};
	127
	128	static struct registry_arena registry_arena;
	129
	130	/* Saved fork signal mask, protected by rcu_gp_lock */
	131	static sigset_t saved_fork_signal_mask;
	132
	133	static void rcu_gc_registry(void);
	134
	135	static void mutex_lock(pthread_mutex_t *mutex)
	136	{
	137	int ret;
	138
	139	#ifndef DISTRUST_SIGNALS_EXTREME
	140	ret = pthread_mutex_lock(mutex);
	141	if (ret)
	142	urcu_die(ret);
	143	#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	144	while ((ret = pthread_mutex_trylock(mutex)) != 0) {
	145	if (ret != EBUSY && ret != EINTR)
	146	urcu_die(ret);
	147	poll(NULL,0,10);
	148	}
	149	#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
	150	}
	151
	152	static void mutex_unlock(pthread_mutex_t *mutex)
	153	{
	154	int ret;
	155
	156	ret = pthread_mutex_unlock(mutex);
	157	if (ret)
	158	urcu_die(ret);
	159	}
	160
	161	static void wait_for_readers(struct cds_list_head *input_readers,
	162	struct cds_list_head *cur_snap_readers,
	163	struct cds_list_head *qsreaders)
	164	{
	165	int wait_loops = 0;
	166	struct rcu_reader index, tmp;
	167
	168	/*
	169	* Wait for each thread URCU_TLS(rcu_reader).ctr to either
	170	* indicate quiescence (not nested), or observe the current
	171	* rcu_gp.ctr value.
	172	*/
	173	for (;;) {
	174	wait_loops++;
	175	cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
	176	switch (rcu_reader_state(&index->ctr)) {
	177	case RCU_READER_ACTIVE_CURRENT:
	178	if (cur_snap_readers) {
	179	cds_list_move(&index->node,
	180	cur_snap_readers);
	181	break;
	182	}
	183	/* Fall-through */
	184	case RCU_READER_INACTIVE:
	185	cds_list_move(&index->node, qsreaders);
	186	break;
	187	case RCU_READER_ACTIVE_OLD:
	188	/*
	189	* Old snapshot. Leaving node in
	190	* input_readers will make us busy-loop
	191	* until the snapshot becomes current or
	192	* the reader becomes inactive.
	193	*/
	194	break;
	195	}
	196	}
	197
	198	if (cds_list_empty(input_readers)) {
	199	break;
	200	} else {
	201	if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
	202	usleep(RCU_SLEEP_DELAY);
	203	else
	204	caa_cpu_relax();
	205	}
	206	}
	207	}
	208
	209	void synchronize_rcu(void)
	210	{
	211	CDS_LIST_HEAD(cur_snap_readers);
	212	CDS_LIST_HEAD(qsreaders);
	213	sigset_t newmask, oldmask;
	214	int ret;
	215
	216	ret = sigfillset(&newmask);
	217	assert(!ret);
	218	ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
	219	assert(!ret);
	220
	221	mutex_lock(&rcu_gp_lock);
	222
	223	if (cds_list_empty(&registry))
	224	goto out;
	225
	226	/* All threads should read qparity before accessing data structure
	227	* where new ptr points to. */
	228	/* Write new ptr before changing the qparity */
	229	cmm_smp_mb();
	230
	231	/* Remove old registry elements */
	232	rcu_gc_registry();
	233
	234	/*
	235	* Wait for readers to observe original parity or be quiescent.
	236	*/
	237	wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
	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	/* Switch parity: 0 -> 1, 1 -> 0 */
	247	CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR_PHASE);
	248
	249	/*
	250	* Must commit qparity update to memory before waiting for other parity
	251	* quiescent state. Failure to do so could result in the writer waiting
	252	* forever while new readers are always accessing data (no progress).
	253	* Ensured by CMM_STORE_SHARED and CMM_LOAD_SHARED.
	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 readers to observe new parity or be quiescent.
	265	*/
	266	wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
	267
	268	/*
	269	* Put quiescent reader list back into registry.
	270	*/
	271	cds_list_splice(&qsreaders, &registry);
	272
	273	/*
	274	* Finish waiting for reader threads before letting the old ptr being
	275	* freed.
	276	*/
	277	cmm_smp_mb();
	278	out:
	279	mutex_unlock(&rcu_gp_lock);
	280	ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
	281	assert(!ret);
	282	}
	283
	284	/*
	285	* library wrappers to be used by non-LGPL compatible source code.
	286	*/
	287
	288	void rcu_read_lock(void)
	289	{
	290	_rcu_read_lock();
	291	}
	292
	293	void rcu_read_unlock(void)
	294	{
	295	_rcu_read_unlock();
	296	}
	297
	298	int rcu_read_ongoing(void)
	299	{
	300	return _rcu_read_ongoing();
	301	}
	302
	303	/*
	304	* only grow for now.
	305	*/
	306	static void resize_arena(struct registry_arena *arena, size_t len)
	307	{
	308	void *new_p;
	309	size_t old_len;
	310
	311	old_len = arena->len;
	312
	313	if (!arena->p)
	314	new_p = mmap(arena->p, len,
	315	PROT_READ \| PROT_WRITE,
	316	MAP_ANONYMOUS \| MAP_PRIVATE,
	317	-1, 0);
	318	else
	319	new_p = mremap_wrapper(arena->p, old_len,
	320	len, MREMAP_MAYMOVE);
	321	assert(new_p != MAP_FAILED);
	322
	323	/*
	324	* Zero the newly allocated memory. Since mmap() does not
	325	* clearly specify if memory is zeroed or not (although it is
	326	* very likely that it is), be extra careful by not expecting
	327	* the new range to be zeroed by mremap.
	328	*/
	329	bzero(new_p + old_len, len - old_len);
	330
	331	/*
	332	* If we did not re-use the same region, we need to update the
	333	* arena pointer.
	334	*/
	335	if (new_p != arena->p)
	336	arena->p = new_p;
	337
	338	arena->len = len;
	339	}
	340
	341	/* Called with signals off and mutex locked */
	342	static void add_thread(void)
	343	{
	344	struct rcu_reader *rcu_reader_reg;
	345
	346	if (registry_arena.len
	347	< registry_arena.used + sizeof(struct rcu_reader))
	348	resize_arena(&registry_arena,
	349	caa_max(registry_arena.len << 1, ARENA_INIT_ALLOC));
	350	/*
	351	* Find a free spot.
	352	*/
	353	for (rcu_reader_reg = registry_arena.p;
	354	(void *)rcu_reader_reg < registry_arena.p + registry_arena.len;
	355	rcu_reader_reg++) {
	356	if (!rcu_reader_reg->alloc)
	357	break;
	358	}
	359	rcu_reader_reg->alloc = 1;
	360	registry_arena.used += sizeof(struct rcu_reader);
	361
	362	/* Add to registry */
	363	rcu_reader_reg->tid = pthread_self();
	364	assert(rcu_reader_reg->ctr == 0);
	365	cds_list_add(&rcu_reader_reg->node, &registry);
	366	URCU_TLS(rcu_reader) = rcu_reader_reg;
	367	}
	368
	369	/* Called with signals off and mutex locked */
	370	static void rcu_gc_registry(void)
	371	{
	372	struct rcu_reader *rcu_reader_reg;
	373	pthread_t tid;
	374	int ret;
	375
	376	for (rcu_reader_reg = registry_arena.p;
	377	(void *)rcu_reader_reg < registry_arena.p + registry_arena.len;
	378	rcu_reader_reg++) {
	379	if (!rcu_reader_reg->alloc)
	380	continue;
	381	tid = rcu_reader_reg->tid;
	382	ret = pthread_kill(tid, 0);
	383	assert(ret != EINVAL);
	384	if (ret == ESRCH) {
	385	cds_list_del(&rcu_reader_reg->node);
	386	rcu_reader_reg->ctr = 0;
	387	rcu_reader_reg->alloc = 0;
	388	registry_arena.used -= sizeof(struct rcu_reader);
	389	}
	390	}
	391	}
	392
	393	/* Disable signals, take mutex, add to registry */
	394	void rcu_bp_register(void)
	395	{
	396	sigset_t newmask, oldmask;
	397	int ret;
	398
	399	ret = sigfillset(&newmask);
	400	assert(!ret);
	401	ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
	402	assert(!ret);
	403
	404	/*
	405	* Check if a signal concurrently registered our thread since
	406	* the check in rcu_read_lock(). */
	407	if (URCU_TLS(rcu_reader))
	408	goto end;
	409
	410	mutex_lock(&rcu_gp_lock);
	411	add_thread();
	412	mutex_unlock(&rcu_gp_lock);
	413	end:
	414	ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
	415	assert(!ret);
	416	}
	417
	418	void rcu_bp_exit(void)
	419	{
	420	if (registry_arena.p)
	421	munmap(registry_arena.p, registry_arena.len);
	422	}
	423
	424	/*
	425	* Holding the rcu_gp_lock across fork will make sure we fork() don't race with
	426	* a concurrent thread executing with this same lock held. This ensures that the
	427	* registry is in a coherent state in the child.
	428	*/
	429	void rcu_bp_before_fork(void)
	430	{
	431	sigset_t newmask, oldmask;
	432	int ret;
	433
	434	ret = sigfillset(&newmask);
	435	assert(!ret);
	436	ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
	437	assert(!ret);
	438	mutex_lock(&rcu_gp_lock);
	439	saved_fork_signal_mask = oldmask;
	440	}
	441
	442	void rcu_bp_after_fork_parent(void)
	443	{
	444	sigset_t oldmask;
	445	int ret;
	446
	447	oldmask = saved_fork_signal_mask;
	448	mutex_unlock(&rcu_gp_lock);
	449	ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
	450	assert(!ret);
	451	}
	452
	453	void rcu_bp_after_fork_child(void)
	454	{
	455	sigset_t oldmask;
	456	int ret;
	457
	458	rcu_gc_registry();
	459	oldmask = saved_fork_signal_mask;
	460	mutex_unlock(&rcu_gp_lock);
	461	ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
	462	assert(!ret);
	463	}
	464
	465	void rcu_dereference_sym_bp(void p)
	466	{
	467	return _rcu_dereference(p);
	468	}
	469
	470	void rcu_set_pointer_sym_bp(void p, void v)
	471	{
	472	cmm_wmb();
	473	uatomic_set(p, v);
	474	return v;
	475	}
	476
	477	void rcu_xchg_pointer_sym_bp(void p, void v)
	478	{
	479	cmm_wmb();
	480	return uatomic_xchg(p, v);
	481	}
	482
	483	void rcu_cmpxchg_pointer_sym_bp(void p, void old, void *_new)
	484	{
	485	cmm_wmb();
	486	return uatomic_cmpxchg(p, old, _new);
	487	}
	488
	489	DEFINE_RCU_FLAVOR(rcu_flavor);
	490
	491	#include "urcu-call-rcu-impl.h"
	492	#include "urcu-defer-impl.h"