Fix: handle sys_futex() FUTEX_WAIT interrupted by signal
[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
80#define MEMBARRIER_EXPEDITED (1 << 0)
81#define MEMBARRIER_DELAYED (1 << 1)
82#define MEMBARRIER_QUERY (1 << 16)
83
fdf01eed 84#ifdef RCU_MEMBARRIER
834a45ba 85static int init_done;
1de4df4b 86int rcu_has_sys_membarrier;
834a45ba 87
02be5561 88void __attribute__((constructor)) rcu_init(void);
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89#endif
90
91#ifdef RCU_MB
02be5561 92void rcu_init(void)
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93{
94}
95#endif
8a5fb4c9 96
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97#ifdef RCU_SIGNAL
98static int init_done;
99
100void __attribute__((constructor)) rcu_init(void);
101void __attribute__((destructor)) rcu_exit(void);
102#endif
103
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104/*
105 * rcu_gp_lock ensures mutual exclusion between threads calling
106 * synchronize_rcu().
107 */
6abb4bd5 108static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
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109/*
110 * rcu_registry_lock ensures mutual exclusion between threads
111 * registering and unregistering themselves to/from the registry, and
112 * with threads reading that registry from synchronize_rcu(). However,
113 * this lock is not held all the way through the completion of awaiting
114 * for the grace period. It is sporadically released between iterations
115 * on the registry.
116 * rcu_registry_lock may nest inside rcu_gp_lock.
117 */
118static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER;
4de0cd31 119struct rcu_gp rcu_gp = { .ctr = RCU_GP_COUNT };
27b012e2 120
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121/*
122 * Written to only by each individual reader. Read by both the reader and the
123 * writers.
124 */
bd252a04 125DEFINE_URCU_TLS(struct rcu_reader, rcu_reader);
27b012e2 126
16aa9ee8 127static CDS_LIST_HEAD(registry);
27b012e2 128
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129/*
130 * Queue keeping threads awaiting to wait for a grace period. Contains
131 * struct gp_waiters_thread objects.
132 */
133static DEFINE_URCU_WAIT_QUEUE(gp_waiters);
134
6abb4bd5 135static void mutex_lock(pthread_mutex_t *mutex)
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136{
137 int ret;
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138
139#ifndef DISTRUST_SIGNALS_EXTREME
6abb4bd5 140 ret = pthread_mutex_lock(mutex);
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141 if (ret)
142 urcu_die(ret);
09a9f986 143#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
6abb4bd5 144 while ((ret = pthread_mutex_trylock(mutex)) != 0) {
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145 if (ret != EBUSY && ret != EINTR)
146 urcu_die(ret);
bd252a04 147 if (CMM_LOAD_SHARED(URCU_TLS(rcu_reader).need_mb)) {
5481ddb3 148 cmm_smp_mb();
bd252a04 149 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
5481ddb3 150 cmm_smp_mb();
09a9f986 151 }
8999a9ee 152 (void) poll(NULL, 0, 10);
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153 }
154#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
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155}
156
6abb4bd5 157static void mutex_unlock(pthread_mutex_t *mutex)
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158{
159 int ret;
160
6abb4bd5 161 ret = pthread_mutex_unlock(mutex);
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162 if (ret)
163 urcu_die(ret);
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164}
165
fdf01eed 166#ifdef RCU_MEMBARRIER
25cc6d18 167static void smp_mb_master(int group)
fdf01eed 168{
1de4df4b 169 if (caa_likely(rcu_has_sys_membarrier))
553b7eb9 170 (void) membarrier(MEMBARRIER_EXPEDITED);
fdf01eed 171 else
5481ddb3 172 cmm_smp_mb();
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173}
174#endif
175
02be5561 176#ifdef RCU_MB
25cc6d18 177static void smp_mb_master(int group)
40e140c9 178{
5481ddb3 179 cmm_smp_mb();
40e140c9 180}
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181#endif
182
183#ifdef RCU_SIGNAL
78ff9419 184static void force_mb_all_readers(void)
27b012e2 185{
02be5561 186 struct rcu_reader *index;
e3b0cef0 187
27b012e2 188 /*
5481ddb3 189 * Ask for each threads to execute a cmm_smp_mb() so we can consider the
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190 * compiler barriers around rcu read lock as real memory barriers.
191 */
16aa9ee8 192 if (cds_list_empty(&registry))
27b012e2 193 return;
3a86deba 194 /*
5481ddb3 195 * pthread_kill has a cmm_smp_mb(). But beware, we assume it performs
157dca95 196 * a cache flush on architectures with non-coherent cache. Let's play
5481ddb3 197 * safe and don't assume anything : we use cmm_smp_mc() to make sure the
157dca95 198 * cache flush is enforced.
3a86deba 199 */
16aa9ee8 200 cds_list_for_each_entry(index, &registry, node) {
6cf3827c 201 CMM_STORE_SHARED(index->need_mb, 1);
02be5561 202 pthread_kill(index->tid, SIGRCU);
09a9f986 203 }
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204 /*
205 * Wait for sighandler (and thus mb()) to execute on every thread.
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206 *
207 * Note that the pthread_kill() will never be executed on systems
208 * that correctly deliver signals in a timely manner. However, it
209 * is not uncommon for kernels to have bugs that can result in
210 * lost or unduly delayed signals.
211 *
212 * If you are seeing the below pthread_kill() executing much at
213 * all, we suggest testing the underlying kernel and filing the
214 * relevant bug report. For Linux kernels, we recommend getting
215 * the Linux Test Project (LTP).
27b012e2 216 */
16aa9ee8 217 cds_list_for_each_entry(index, &registry, node) {
6cf3827c 218 while (CMM_LOAD_SHARED(index->need_mb)) {
02be5561 219 pthread_kill(index->tid, SIGRCU);
8999a9ee 220 (void) poll(NULL, 0, 1);
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221 }
222 }
5481ddb3 223 cmm_smp_mb(); /* read ->need_mb before ending the barrier */
27b012e2 224}
9d7e3f89 225
25cc6d18 226static void smp_mb_master(int group)
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227{
228 force_mb_all_readers();
229}
fdf01eed 230#endif /* #ifdef RCU_SIGNAL */
27b012e2 231
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232/*
233 * synchronize_rcu() waiting. Single thread.
234 */
cfe78e25 235static void wait_gp(void)
bc6c15bb 236{
cfe78e25 237 /* Read reader_gp before read futex */
25cc6d18 238 smp_mb_master(RCU_MB_GROUP);
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239 if (uatomic_read(&rcu_gp.futex) != -1)
240 return;
241 while (futex_async(&rcu_gp.futex, FUTEX_WAIT, -1,
242 NULL, NULL, 0)) {
243 switch (errno) {
244 case EWOULDBLOCK:
245 /* Value already changed. */
246 return;
247 case EINTR:
248 /* Retry if interrupted by signal. */
249 break; /* Get out of switch. */
250 default:
251 /* Unexpected error. */
252 urcu_die(errno);
253 }
254 }
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255}
256
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257/*
258 * Always called with rcu_registry lock held. Releases this lock between
259 * iterations and grabs it again. Holds the lock when it returns.
260 */
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261static void wait_for_readers(struct cds_list_head *input_readers,
262 struct cds_list_head *cur_snap_readers,
263 struct cds_list_head *qsreaders)
27b012e2 264{
9340c38d 265 unsigned int wait_loops = 0;
02be5561 266 struct rcu_reader *index, *tmp;
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267#ifdef HAS_INCOHERENT_CACHES
268 unsigned int wait_gp_loops = 0;
269#endif /* HAS_INCOHERENT_CACHES */
27b012e2 270
40e140c9 271 /*
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272 * Wait for each thread URCU_TLS(rcu_reader).ctr to either
273 * indicate quiescence (not nested), or observe the current
ed1b099e 274 * rcu_gp.ctr value.
27b012e2 275 */
cfe78e25 276 for (;;) {
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277 if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
278 wait_loops++;
9340c38d 279 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
ed1b099e 280 uatomic_dec(&rcu_gp.futex);
cfe78e25 281 /* Write futex before read reader_gp */
25cc6d18 282 smp_mb_master(RCU_MB_GROUP);
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283 }
284
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285 cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
286 switch (rcu_reader_state(&index->ctr)) {
287 case RCU_READER_ACTIVE_CURRENT:
288 if (cur_snap_readers) {
289 cds_list_move(&index->node,
290 cur_snap_readers);
291 break;
292 }
293 /* Fall-through */
294 case RCU_READER_INACTIVE:
295 cds_list_move(&index->node, qsreaders);
296 break;
297 case RCU_READER_ACTIVE_OLD:
298 /*
299 * Old snapshot. Leaving node in
300 * input_readers will make us busy-loop
301 * until the snapshot becomes current or
302 * the reader becomes inactive.
303 */
304 break;
305 }
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306 }
307
e8043c1b 308#ifndef HAS_INCOHERENT_CACHES
fd189fa5 309 if (cds_list_empty(input_readers)) {
9340c38d 310 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
cfe78e25 311 /* Read reader_gp before write futex */
25cc6d18 312 smp_mb_master(RCU_MB_GROUP);
ed1b099e 313 uatomic_set(&rcu_gp.futex, 0);
bc6c15bb 314 }
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315 break;
316 } else {
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317 /* Temporarily unlock the registry lock. */
318 mutex_unlock(&rcu_registry_lock);
9340c38d 319 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS)
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320 wait_gp();
321 else
06f22bdb 322 caa_cpu_relax();
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323 /* Re-lock the registry lock before the next loop. */
324 mutex_lock(&rcu_registry_lock);
bc6c15bb 325 }
e8043c1b 326#else /* #ifndef HAS_INCOHERENT_CACHES */
27b012e2 327 /*
40e140c9 328 * BUSY-LOOP. Force the reader thread to commit its
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329 * URCU_TLS(rcu_reader).ctr update to memory if we wait
330 * for too long.
27b012e2 331 */
fd189fa5 332 if (cds_list_empty(input_readers)) {
9340c38d 333 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
cfe78e25 334 /* Read reader_gp before write futex */
25cc6d18 335 smp_mb_master(RCU_MB_GROUP);
ed1b099e 336 uatomic_set(&rcu_gp.futex, 0);
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337 }
338 break;
339 } else {
9340c38d 340 if (wait_gp_loops == KICK_READER_LOOPS) {
25cc6d18 341 smp_mb_master(RCU_MB_GROUP);
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342 wait_gp_loops = 0;
343 }
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344 /* Temporarily unlock the registry lock. */
345 mutex_unlock(&rcu_registry_lock);
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346 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
347 wait_gp();
348 wait_gp_loops++;
349 } else {
06f22bdb 350 caa_cpu_relax();
40e140c9 351 }
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352 /* Re-lock the registry lock before the next loop. */
353 mutex_lock(&rcu_registry_lock);
40e140c9 354 }
e8043c1b 355#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
27b012e2 356 }
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357}
358
9598a481 359void synchronize_rcu(void)
2bc59bd7 360{
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361 CDS_LIST_HEAD(cur_snap_readers);
362 CDS_LIST_HEAD(qsreaders);
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363 DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
364 struct urcu_waiters waiters;
365
366 /*
367 * Add ourself to gp_waiters queue of threads awaiting to wait
368 * for a grace period. Proceed to perform the grace period only
369 * if we are the first thread added into the queue.
370 * The implicit memory barrier before urcu_wait_add()
371 * orders prior memory accesses of threads put into the wait
372 * queue before their insertion into the wait queue.
373 */
374 if (urcu_wait_add(&gp_waiters, &wait) != 0) {
375 /* Not first in queue: will be awakened by another thread. */
376 urcu_adaptative_busy_wait(&wait);
377 /* Order following memory accesses after grace period. */
378 cmm_smp_mb();
379 return;
380 }
381 /* We won't need to wake ourself up */
382 urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);
fd189fa5 383
6abb4bd5 384 mutex_lock(&rcu_gp_lock);
135530fd 385
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386 /*
387 * Move all waiters into our local queue.
388 */
389 urcu_move_waiters(&waiters, &gp_waiters);
390
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391 mutex_lock(&rcu_registry_lock);
392
16aa9ee8 393 if (cds_list_empty(&registry))
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394 goto out;
395
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396 /*
397 * All threads should read qparity before accessing data structure
398 * where new ptr points to. Must be done within rcu_registry_lock
399 * because it iterates on reader threads.
400 */
9598a481 401 /* Write new ptr before changing the qparity */
25cc6d18 402 smp_mb_master(RCU_MB_GROUP);
9598a481 403
9598a481 404 /*
c9488684 405 * Wait for readers to observe original parity or be quiescent.
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406 * wait_for_readers() can release and grab again rcu_registry_lock
407 * interally.
9598a481 408 */
fd189fa5 409 wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
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410
411 /*
c9488684 412 * Must finish waiting for quiescent state for original parity before
ed1b099e 413 * committing next rcu_gp.ctr update to memory. Failure to do so could
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414 * result in the writer waiting forever while new readers are always
415 * accessing data (no progress). Enforce compiler-order of load
ed1b099e 416 * URCU_TLS(rcu_reader).ctr before store to rcu_gp.ctr.
9598a481 417 */
5481ddb3 418 cmm_barrier();
9598a481 419
5dba80f9 420 /*
5481ddb3 421 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
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422 * model easier to understand. It does not have a big performance impact
423 * anyway, given this is the write-side.
424 */
5481ddb3 425 cmm_smp_mb();
67c2d80b 426
c9488684 427 /* Switch parity: 0 -> 1, 1 -> 0 */
ed1b099e 428 CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR_PHASE);
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429
430 /*
ed1b099e 431 * Must commit rcu_gp.ctr update to memory before waiting for quiescent
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432 * state. Failure to do so could result in the writer waiting forever
433 * while new readers are always accessing data (no progress). Enforce
ed1b099e 434 * compiler-order of store to rcu_gp.ctr before load rcu_reader ctr.
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435 */
436 cmm_barrier();
437
438 /*
439 *
440 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
441 * model easier to understand. It does not have a big performance impact
442 * anyway, given this is the write-side.
443 */
444 cmm_smp_mb();
445
9598a481 446 /*
c9488684 447 * Wait for readers to observe new parity or be quiescent.
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448 * wait_for_readers() can release and grab again rcu_registry_lock
449 * interally.
9598a481 450 */
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451 wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
452
453 /*
454 * Put quiescent reader list back into registry.
455 */
456 cds_list_splice(&qsreaders, &registry);
9598a481 457
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458 /*
459 * Finish waiting for reader threads before letting the old ptr
460 * being freed. Must be done within rcu_registry_lock because it
461 * iterates on reader threads.
462 */
25cc6d18 463 smp_mb_master(RCU_MB_GROUP);
2dfb8b5e 464out:
731ccb96 465 mutex_unlock(&rcu_registry_lock);
6abb4bd5 466 mutex_unlock(&rcu_gp_lock);
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467
468 /*
469 * Wakeup waiters only after we have completed the grace period
470 * and have ensured the memory barriers at the end of the grace
471 * period have been issued.
472 */
473 urcu_wake_all_waiters(&waiters);
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474}
475
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476/*
477 * library wrappers to be used by non-LGPL compatible source code.
478 */
479
480void rcu_read_lock(void)
481{
482 _rcu_read_lock();
483}
484
485void rcu_read_unlock(void)
486{
487 _rcu_read_unlock();
488}
489
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490int rcu_read_ongoing(void)
491{
492 return _rcu_read_ongoing();
493}
494
121a5d44 495void rcu_register_thread(void)
27b012e2 496{
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497 URCU_TLS(rcu_reader).tid = pthread_self();
498 assert(URCU_TLS(rcu_reader).need_mb == 0);
499 assert(!(URCU_TLS(rcu_reader).ctr & RCU_GP_CTR_NEST_MASK));
02be5561 500
731ccb96 501 mutex_lock(&rcu_registry_lock);
02be5561 502 rcu_init(); /* In case gcc does not support constructor attribute */
bd252a04 503 cds_list_add(&URCU_TLS(rcu_reader).node, &registry);
731ccb96 504 mutex_unlock(&rcu_registry_lock);
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505}
506
121a5d44 507void rcu_unregister_thread(void)
27b012e2 508{
731ccb96 509 mutex_lock(&rcu_registry_lock);
bd252a04 510 cds_list_del(&URCU_TLS(rcu_reader).node);
731ccb96 511 mutex_unlock(&rcu_registry_lock);
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512}
513
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514#ifdef RCU_MEMBARRIER
515void rcu_init(void)
516{
517 if (init_done)
518 return;
519 init_done = 1;
cf5271ee 520 if (!membarrier(MEMBARRIER_EXPEDITED | MEMBARRIER_QUERY))
1de4df4b 521 rcu_has_sys_membarrier = 1;
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522}
523#endif
524
525#ifdef RCU_SIGNAL
02be5561 526static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context)
27b012e2 527{
40e140c9 528 /*
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529 * Executing this cmm_smp_mb() is the only purpose of this signal handler.
530 * It punctually promotes cmm_barrier() into cmm_smp_mb() on every thread it is
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531 * executed on.
532 */
5481ddb3 533 cmm_smp_mb();
bd252a04 534 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
5481ddb3 535 cmm_smp_mb();
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536}
537
8a5fb4c9 538/*
02be5561 539 * rcu_init constructor. Called when the library is linked, but also when
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540 * reader threads are calling rcu_register_thread().
541 * Should only be called by a single thread at a given time. This is ensured by
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542 * holing the rcu_registry_lock from rcu_register_thread() or by running
543 * at library load time, which should not be executed by multiple
544 * threads nor concurrently with rcu_register_thread() anyway.
8a5fb4c9 545 */
02be5561 546void rcu_init(void)
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547{
548 struct sigaction act;
549 int ret;
550
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551 if (init_done)
552 return;
553 init_done = 1;
554
02be5561 555 act.sa_sigaction = sigrcu_handler;
dd052bd3 556 act.sa_flags = SA_SIGINFO | SA_RESTART;
c297c21c 557 sigemptyset(&act.sa_mask);
02be5561 558 ret = sigaction(SIGRCU, &act, NULL);
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559 if (ret)
560 urcu_die(errno);
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561}
562
02be5561 563void rcu_exit(void)
27b012e2 564{
71210954
MD
565 /*
566 * Don't unregister the SIGRCU signal handler anymore, because
567 * call_rcu threads could still be using it shortly before the
568 * application exits.
569 * Assertion disabled because call_rcu threads are now rcu
570 * readers, and left running at exit.
571 * assert(cds_list_empty(&registry));
572 */
27b012e2 573}
5e77fc1f 574
fdf01eed 575#endif /* #ifdef RCU_SIGNAL */
5e77fc1f 576
5e6b23a6 577DEFINE_RCU_FLAVOR(rcu_flavor);
541d828d 578
5e77fc1f 579#include "urcu-call-rcu-impl.h"
0376e7b2 580#include "urcu-defer-impl.h"
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