Update following changes to sys_membarrier ABI
[urcu.git] / urcu.c
CommitLineData
b257a10b
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1/*
2 * urcu.c
3 *
4 * Userspace RCU library
5 *
6982d6d7 6 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
af02d47e 7 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
b257a10b 8 *
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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
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22 *
23 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
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24 */
25
fdf01eed 26#define _BSD_SOURCE
c1d2c60b 27#define _GNU_SOURCE
71c811bf 28#define _LGPL_SOURCE
82d50e1a 29#define _DEFAULT_SOURCE
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30#include <stdio.h>
31#include <pthread.h>
32#include <signal.h>
33#include <assert.h>
f69f195a 34#include <stdlib.h>
6d841bc2 35#include <stdint.h>
f69f195a 36#include <string.h>
09a9f986 37#include <errno.h>
e8043c1b 38#include <poll.h>
27b012e2 39
d73fb81f 40#include "urcu/wfcqueue.h"
57760d44 41#include "urcu/map/urcu.h"
af7c2dbe 42#include "urcu/static/urcu.h"
618b2595 43#include "urcu-pointer.h"
bd252a04 44#include "urcu/tls-compat.h"
71c811bf 45
4a6d7378 46#include "urcu-die.h"
5bffdd5d 47#include "urcu-wait.h"
4a6d7378 48
121a5d44 49/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
71c811bf 50#undef _LGPL_SOURCE
27b012e2 51#include "urcu.h"
71c811bf 52#define _LGPL_SOURCE
27b012e2 53
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54/*
55 * If a reader is really non-cooperative and refuses to commit its
56 * rcu_active_readers count to memory (there is no barrier in the reader
9340c38d 57 * per-se), kick it after 10 loops waiting for it.
3a71751e 58 */
9340c38d 59#define KICK_READER_LOOPS 10
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60
61/*
62 * Active attempts to check for reader Q.S. before calling futex().
63 */
64#define RCU_QS_ACTIVE_ATTEMPTS 100
65
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66/*
67 * RCU_MEMBARRIER is only possibly available on Linux.
68 */
69#if defined(RCU_MEMBARRIER) && defined(__linux__)
9ba261bd 70#include <urcu/syscall-compat.h>
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71#endif
72
73/* If the headers do not support SYS_membarrier, fall back on RCU_MB */
74#ifdef SYS_membarrier
75# define membarrier(...) syscall(SYS_membarrier, __VA_ARGS__)
76#else
77# define membarrier(...) -ENOSYS
78#endif
79
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80enum membarrier_cmd {
81 MEMBARRIER_CMD_QUERY = 0,
82 MEMBARRIER_CMD_SHARED = (1 << 0),
83};
553b7eb9 84
fdf01eed 85#ifdef RCU_MEMBARRIER
834a45ba 86static int init_done;
1de4df4b 87int rcu_has_sys_membarrier;
834a45ba 88
02be5561 89void __attribute__((constructor)) rcu_init(void);
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90#endif
91
92#ifdef RCU_MB
02be5561 93void rcu_init(void)
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94{
95}
96#endif
8a5fb4c9 97
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98#ifdef RCU_SIGNAL
99static int init_done;
100
101void __attribute__((constructor)) rcu_init(void);
102void __attribute__((destructor)) rcu_exit(void);
103#endif
104
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105/*
106 * rcu_gp_lock ensures mutual exclusion between threads calling
107 * synchronize_rcu().
108 */
6abb4bd5 109static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
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110/*
111 * rcu_registry_lock ensures mutual exclusion between threads
112 * registering and unregistering themselves to/from the registry, and
113 * with threads reading that registry from synchronize_rcu(). However,
114 * this lock is not held all the way through the completion of awaiting
115 * for the grace period. It is sporadically released between iterations
116 * on the registry.
117 * rcu_registry_lock may nest inside rcu_gp_lock.
118 */
119static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER;
4de0cd31 120struct rcu_gp rcu_gp = { .ctr = RCU_GP_COUNT };
27b012e2 121
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122/*
123 * Written to only by each individual reader. Read by both the reader and the
124 * writers.
125 */
bd252a04 126DEFINE_URCU_TLS(struct rcu_reader, rcu_reader);
27b012e2 127
16aa9ee8 128static CDS_LIST_HEAD(registry);
27b012e2 129
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130/*
131 * Queue keeping threads awaiting to wait for a grace period. Contains
132 * struct gp_waiters_thread objects.
133 */
134static DEFINE_URCU_WAIT_QUEUE(gp_waiters);
135
6abb4bd5 136static void mutex_lock(pthread_mutex_t *mutex)
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137{
138 int ret;
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139
140#ifndef DISTRUST_SIGNALS_EXTREME
6abb4bd5 141 ret = pthread_mutex_lock(mutex);
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142 if (ret)
143 urcu_die(ret);
09a9f986 144#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
6abb4bd5 145 while ((ret = pthread_mutex_trylock(mutex)) != 0) {
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146 if (ret != EBUSY && ret != EINTR)
147 urcu_die(ret);
bd252a04 148 if (CMM_LOAD_SHARED(URCU_TLS(rcu_reader).need_mb)) {
5481ddb3 149 cmm_smp_mb();
bd252a04 150 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
5481ddb3 151 cmm_smp_mb();
09a9f986 152 }
8999a9ee 153 (void) poll(NULL, 0, 10);
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154 }
155#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
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156}
157
6abb4bd5 158static void mutex_unlock(pthread_mutex_t *mutex)
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159{
160 int ret;
161
6abb4bd5 162 ret = pthread_mutex_unlock(mutex);
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163 if (ret)
164 urcu_die(ret);
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165}
166
fdf01eed 167#ifdef RCU_MEMBARRIER
25cc6d18 168static void smp_mb_master(int group)
fdf01eed 169{
1de4df4b 170 if (caa_likely(rcu_has_sys_membarrier))
64f469e6 171 (void) membarrier(MEMBARRIER_CMD_SHARED, 0);
fdf01eed 172 else
5481ddb3 173 cmm_smp_mb();
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174}
175#endif
176
02be5561 177#ifdef RCU_MB
25cc6d18 178static void smp_mb_master(int group)
40e140c9 179{
5481ddb3 180 cmm_smp_mb();
40e140c9 181}
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182#endif
183
184#ifdef RCU_SIGNAL
78ff9419 185static void force_mb_all_readers(void)
27b012e2 186{
02be5561 187 struct rcu_reader *index;
e3b0cef0 188
27b012e2 189 /*
5481ddb3 190 * Ask for each threads to execute a cmm_smp_mb() so we can consider the
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191 * compiler barriers around rcu read lock as real memory barriers.
192 */
16aa9ee8 193 if (cds_list_empty(&registry))
27b012e2 194 return;
3a86deba 195 /*
5481ddb3 196 * pthread_kill has a cmm_smp_mb(). But beware, we assume it performs
157dca95 197 * a cache flush on architectures with non-coherent cache. Let's play
5481ddb3 198 * safe and don't assume anything : we use cmm_smp_mc() to make sure the
157dca95 199 * cache flush is enforced.
3a86deba 200 */
16aa9ee8 201 cds_list_for_each_entry(index, &registry, node) {
6cf3827c 202 CMM_STORE_SHARED(index->need_mb, 1);
02be5561 203 pthread_kill(index->tid, SIGRCU);
09a9f986 204 }
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205 /*
206 * Wait for sighandler (and thus mb()) to execute on every thread.
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207 *
208 * Note that the pthread_kill() will never be executed on systems
209 * that correctly deliver signals in a timely manner. However, it
210 * is not uncommon for kernels to have bugs that can result in
211 * lost or unduly delayed signals.
212 *
213 * If you are seeing the below pthread_kill() executing much at
214 * all, we suggest testing the underlying kernel and filing the
215 * relevant bug report. For Linux kernels, we recommend getting
216 * the Linux Test Project (LTP).
27b012e2 217 */
16aa9ee8 218 cds_list_for_each_entry(index, &registry, node) {
6cf3827c 219 while (CMM_LOAD_SHARED(index->need_mb)) {
02be5561 220 pthread_kill(index->tid, SIGRCU);
8999a9ee 221 (void) poll(NULL, 0, 1);
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222 }
223 }
5481ddb3 224 cmm_smp_mb(); /* read ->need_mb before ending the barrier */
27b012e2 225}
9d7e3f89 226
25cc6d18 227static void smp_mb_master(int group)
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228{
229 force_mb_all_readers();
230}
fdf01eed 231#endif /* #ifdef RCU_SIGNAL */
27b012e2 232
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233/*
234 * synchronize_rcu() waiting. Single thread.
235 */
cfe78e25 236static void wait_gp(void)
bc6c15bb 237{
cfe78e25 238 /* Read reader_gp before read futex */
25cc6d18 239 smp_mb_master(RCU_MB_GROUP);
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240 if (uatomic_read(&rcu_gp.futex) != -1)
241 return;
242 while (futex_async(&rcu_gp.futex, FUTEX_WAIT, -1,
243 NULL, NULL, 0)) {
244 switch (errno) {
245 case EWOULDBLOCK:
246 /* Value already changed. */
247 return;
248 case EINTR:
249 /* Retry if interrupted by signal. */
250 break; /* Get out of switch. */
251 default:
252 /* Unexpected error. */
253 urcu_die(errno);
254 }
255 }
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256}
257
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258/*
259 * Always called with rcu_registry lock held. Releases this lock between
260 * iterations and grabs it again. Holds the lock when it returns.
261 */
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262static void wait_for_readers(struct cds_list_head *input_readers,
263 struct cds_list_head *cur_snap_readers,
264 struct cds_list_head *qsreaders)
27b012e2 265{
9340c38d 266 unsigned int wait_loops = 0;
02be5561 267 struct rcu_reader *index, *tmp;
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268#ifdef HAS_INCOHERENT_CACHES
269 unsigned int wait_gp_loops = 0;
270#endif /* HAS_INCOHERENT_CACHES */
27b012e2 271
40e140c9 272 /*
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273 * Wait for each thread URCU_TLS(rcu_reader).ctr to either
274 * indicate quiescence (not nested), or observe the current
ed1b099e 275 * rcu_gp.ctr value.
27b012e2 276 */
cfe78e25 277 for (;;) {
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278 if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
279 wait_loops++;
9340c38d 280 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
ed1b099e 281 uatomic_dec(&rcu_gp.futex);
cfe78e25 282 /* Write futex before read reader_gp */
25cc6d18 283 smp_mb_master(RCU_MB_GROUP);
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284 }
285
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286 cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
287 switch (rcu_reader_state(&index->ctr)) {
288 case RCU_READER_ACTIVE_CURRENT:
289 if (cur_snap_readers) {
290 cds_list_move(&index->node,
291 cur_snap_readers);
292 break;
293 }
294 /* Fall-through */
295 case RCU_READER_INACTIVE:
296 cds_list_move(&index->node, qsreaders);
297 break;
298 case RCU_READER_ACTIVE_OLD:
299 /*
300 * Old snapshot. Leaving node in
301 * input_readers will make us busy-loop
302 * until the snapshot becomes current or
303 * the reader becomes inactive.
304 */
305 break;
306 }
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307 }
308
e8043c1b 309#ifndef HAS_INCOHERENT_CACHES
fd189fa5 310 if (cds_list_empty(input_readers)) {
9340c38d 311 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
cfe78e25 312 /* Read reader_gp before write futex */
25cc6d18 313 smp_mb_master(RCU_MB_GROUP);
ed1b099e 314 uatomic_set(&rcu_gp.futex, 0);
bc6c15bb 315 }
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316 break;
317 } else {
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318 /* Temporarily unlock the registry lock. */
319 mutex_unlock(&rcu_registry_lock);
9340c38d 320 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS)
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321 wait_gp();
322 else
06f22bdb 323 caa_cpu_relax();
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324 /* Re-lock the registry lock before the next loop. */
325 mutex_lock(&rcu_registry_lock);
bc6c15bb 326 }
e8043c1b 327#else /* #ifndef HAS_INCOHERENT_CACHES */
27b012e2 328 /*
40e140c9 329 * BUSY-LOOP. Force the reader thread to commit its
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330 * URCU_TLS(rcu_reader).ctr update to memory if we wait
331 * for too long.
27b012e2 332 */
fd189fa5 333 if (cds_list_empty(input_readers)) {
9340c38d 334 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
cfe78e25 335 /* Read reader_gp before write futex */
25cc6d18 336 smp_mb_master(RCU_MB_GROUP);
ed1b099e 337 uatomic_set(&rcu_gp.futex, 0);
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338 }
339 break;
340 } else {
9340c38d 341 if (wait_gp_loops == KICK_READER_LOOPS) {
25cc6d18 342 smp_mb_master(RCU_MB_GROUP);
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343 wait_gp_loops = 0;
344 }
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345 /* Temporarily unlock the registry lock. */
346 mutex_unlock(&rcu_registry_lock);
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347 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
348 wait_gp();
349 wait_gp_loops++;
350 } else {
06f22bdb 351 caa_cpu_relax();
40e140c9 352 }
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353 /* Re-lock the registry lock before the next loop. */
354 mutex_lock(&rcu_registry_lock);
40e140c9 355 }
e8043c1b 356#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
27b012e2 357 }
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358}
359
9598a481 360void synchronize_rcu(void)
2bc59bd7 361{
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362 CDS_LIST_HEAD(cur_snap_readers);
363 CDS_LIST_HEAD(qsreaders);
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364 DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
365 struct urcu_waiters waiters;
366
367 /*
368 * Add ourself to gp_waiters queue of threads awaiting to wait
369 * for a grace period. Proceed to perform the grace period only
370 * if we are the first thread added into the queue.
371 * The implicit memory barrier before urcu_wait_add()
372 * orders prior memory accesses of threads put into the wait
373 * queue before their insertion into the wait queue.
374 */
375 if (urcu_wait_add(&gp_waiters, &wait) != 0) {
376 /* Not first in queue: will be awakened by another thread. */
377 urcu_adaptative_busy_wait(&wait);
378 /* Order following memory accesses after grace period. */
379 cmm_smp_mb();
380 return;
381 }
382 /* We won't need to wake ourself up */
383 urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);
fd189fa5 384
6abb4bd5 385 mutex_lock(&rcu_gp_lock);
135530fd 386
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387 /*
388 * Move all waiters into our local queue.
389 */
390 urcu_move_waiters(&waiters, &gp_waiters);
391
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392 mutex_lock(&rcu_registry_lock);
393
16aa9ee8 394 if (cds_list_empty(&registry))
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395 goto out;
396
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397 /*
398 * All threads should read qparity before accessing data structure
399 * where new ptr points to. Must be done within rcu_registry_lock
400 * because it iterates on reader threads.
401 */
9598a481 402 /* Write new ptr before changing the qparity */
25cc6d18 403 smp_mb_master(RCU_MB_GROUP);
9598a481 404
9598a481 405 /*
c9488684 406 * Wait for readers to observe original parity or be quiescent.
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407 * wait_for_readers() can release and grab again rcu_registry_lock
408 * interally.
9598a481 409 */
fd189fa5 410 wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
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411
412 /*
c9488684 413 * Must finish waiting for quiescent state for original parity before
ed1b099e 414 * committing next rcu_gp.ctr update to memory. Failure to do so could
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415 * result in the writer waiting forever while new readers are always
416 * accessing data (no progress). Enforce compiler-order of load
ed1b099e 417 * URCU_TLS(rcu_reader).ctr before store to rcu_gp.ctr.
9598a481 418 */
5481ddb3 419 cmm_barrier();
9598a481 420
5dba80f9 421 /*
5481ddb3 422 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
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423 * model easier to understand. It does not have a big performance impact
424 * anyway, given this is the write-side.
425 */
5481ddb3 426 cmm_smp_mb();
67c2d80b 427
c9488684 428 /* Switch parity: 0 -> 1, 1 -> 0 */
ed1b099e 429 CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR_PHASE);
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430
431 /*
ed1b099e 432 * Must commit rcu_gp.ctr update to memory before waiting for quiescent
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433 * state. Failure to do so could result in the writer waiting forever
434 * while new readers are always accessing data (no progress). Enforce
ed1b099e 435 * compiler-order of store to rcu_gp.ctr before load rcu_reader ctr.
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436 */
437 cmm_barrier();
438
439 /*
440 *
441 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
442 * model easier to understand. It does not have a big performance impact
443 * anyway, given this is the write-side.
444 */
445 cmm_smp_mb();
446
9598a481 447 /*
c9488684 448 * Wait for readers to observe new parity or be quiescent.
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449 * wait_for_readers() can release and grab again rcu_registry_lock
450 * interally.
9598a481 451 */
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452 wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
453
454 /*
455 * Put quiescent reader list back into registry.
456 */
457 cds_list_splice(&qsreaders, &registry);
9598a481 458
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459 /*
460 * Finish waiting for reader threads before letting the old ptr
461 * being freed. Must be done within rcu_registry_lock because it
462 * iterates on reader threads.
463 */
25cc6d18 464 smp_mb_master(RCU_MB_GROUP);
2dfb8b5e 465out:
731ccb96 466 mutex_unlock(&rcu_registry_lock);
6abb4bd5 467 mutex_unlock(&rcu_gp_lock);
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468
469 /*
470 * Wakeup waiters only after we have completed the grace period
471 * and have ensured the memory barriers at the end of the grace
472 * period have been issued.
473 */
474 urcu_wake_all_waiters(&waiters);
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475}
476
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477/*
478 * library wrappers to be used by non-LGPL compatible source code.
479 */
480
481void rcu_read_lock(void)
482{
483 _rcu_read_lock();
484}
485
486void rcu_read_unlock(void)
487{
488 _rcu_read_unlock();
489}
490
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491int rcu_read_ongoing(void)
492{
493 return _rcu_read_ongoing();
494}
495
121a5d44 496void rcu_register_thread(void)
27b012e2 497{
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498 URCU_TLS(rcu_reader).tid = pthread_self();
499 assert(URCU_TLS(rcu_reader).need_mb == 0);
500 assert(!(URCU_TLS(rcu_reader).ctr & RCU_GP_CTR_NEST_MASK));
02be5561 501
731ccb96 502 mutex_lock(&rcu_registry_lock);
02be5561 503 rcu_init(); /* In case gcc does not support constructor attribute */
bd252a04 504 cds_list_add(&URCU_TLS(rcu_reader).node, &registry);
731ccb96 505 mutex_unlock(&rcu_registry_lock);
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506}
507
121a5d44 508void rcu_unregister_thread(void)
27b012e2 509{
731ccb96 510 mutex_lock(&rcu_registry_lock);
bd252a04 511 cds_list_del(&URCU_TLS(rcu_reader).node);
731ccb96 512 mutex_unlock(&rcu_registry_lock);
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513}
514
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515#ifdef RCU_MEMBARRIER
516void rcu_init(void)
517{
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518 int ret;
519
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520 if (init_done)
521 return;
522 init_done = 1;
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523 ret = membarrier(MEMBARRIER_CMD_QUERY, 0);
524 if (ret >= 0 && (ret & MEMBARRIER_CMD_SHARED)) {
1de4df4b 525 rcu_has_sys_membarrier = 1;
64f469e6 526 }
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527}
528#endif
529
530#ifdef RCU_SIGNAL
02be5561 531static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context)
27b012e2 532{
40e140c9 533 /*
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534 * Executing this cmm_smp_mb() is the only purpose of this signal handler.
535 * It punctually promotes cmm_barrier() into cmm_smp_mb() on every thread it is
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536 * executed on.
537 */
5481ddb3 538 cmm_smp_mb();
bd252a04 539 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
5481ddb3 540 cmm_smp_mb();
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541}
542
8a5fb4c9 543/*
02be5561 544 * rcu_init constructor. Called when the library is linked, but also when
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545 * reader threads are calling rcu_register_thread().
546 * Should only be called by a single thread at a given time. This is ensured by
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547 * holing the rcu_registry_lock from rcu_register_thread() or by running
548 * at library load time, which should not be executed by multiple
549 * threads nor concurrently with rcu_register_thread() anyway.
8a5fb4c9 550 */
02be5561 551void rcu_init(void)
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552{
553 struct sigaction act;
554 int ret;
555
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556 if (init_done)
557 return;
558 init_done = 1;
559
02be5561 560 act.sa_sigaction = sigrcu_handler;
dd052bd3 561 act.sa_flags = SA_SIGINFO | SA_RESTART;
c297c21c 562 sigemptyset(&act.sa_mask);
02be5561 563 ret = sigaction(SIGRCU, &act, NULL);
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564 if (ret)
565 urcu_die(errno);
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566}
567
02be5561 568void rcu_exit(void)
27b012e2 569{
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570 /*
571 * Don't unregister the SIGRCU signal handler anymore, because
572 * call_rcu threads could still be using it shortly before the
573 * application exits.
574 * Assertion disabled because call_rcu threads are now rcu
575 * readers, and left running at exit.
576 * assert(cds_list_empty(&registry));
577 */
27b012e2 578}
5e77fc1f 579
fdf01eed 580#endif /* #ifdef RCU_SIGNAL */
5e77fc1f 581
5e6b23a6 582DEFINE_RCU_FLAVOR(rcu_flavor);
541d828d 583
5e77fc1f 584#include "urcu-call-rcu-impl.h"
0376e7b2 585#include "urcu-defer-impl.h"
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