urcu,call_rcu: Cleanup call_rcu_data pointers before use in child
[urcu.git] / urcu.c
CommitLineData
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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
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29#include <stdio.h>
30#include <pthread.h>
31#include <signal.h>
32#include <assert.h>
f69f195a 33#include <stdlib.h>
6d841bc2 34#include <stdint.h>
f69f195a 35#include <string.h>
09a9f986 36#include <errno.h>
e8043c1b 37#include <poll.h>
27b012e2 38
71c811bf 39#include "urcu/wfqueue.h"
57760d44 40#include "urcu/map/urcu.h"
af7c2dbe 41#include "urcu/static/urcu.h"
71c811bf 42
121a5d44 43/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
71c811bf 44#undef _LGPL_SOURCE
27b012e2 45#include "urcu.h"
71c811bf 46#define _LGPL_SOURCE
27b012e2 47
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48/*
49 * If a reader is really non-cooperative and refuses to commit its
50 * rcu_active_readers count to memory (there is no barrier in the reader
51 * per-se), kick it after a few loops waiting for it.
52 */
53#define KICK_READER_LOOPS 10000
54
55/*
56 * Active attempts to check for reader Q.S. before calling futex().
57 */
58#define RCU_QS_ACTIVE_ATTEMPTS 100
59
fdf01eed 60#ifdef RCU_MEMBARRIER
834a45ba 61static int init_done;
fdf01eed 62int has_sys_membarrier;
834a45ba 63
02be5561 64void __attribute__((constructor)) rcu_init(void);
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65#endif
66
67#ifdef RCU_MB
02be5561 68void rcu_init(void)
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69{
70}
71#endif
8a5fb4c9 72
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73#ifdef RCU_SIGNAL
74static int init_done;
75
76void __attribute__((constructor)) rcu_init(void);
77void __attribute__((destructor)) rcu_exit(void);
78#endif
79
6abb4bd5 80static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
27b012e2 81
6d841bc2 82int32_t gp_futex;
bc6c15bb 83
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84/*
85 * Global grace period counter.
02be5561 86 * Contains the current RCU_GP_CTR_PHASE.
afb8f2c9 87 * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
b0d5e790 88 * Written to only by writer with mutex taken. Read by both writer and readers.
128166c9 89 */
27d65bc5 90unsigned long rcu_gp_ctr = RCU_GP_COUNT;
27b012e2 91
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92/*
93 * Written to only by each individual reader. Read by both the reader and the
94 * writers.
95 */
02be5561 96struct rcu_reader __thread rcu_reader;
27b012e2 97
cf380c2f 98#ifdef DEBUG_YIELD
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99unsigned int yield_active;
100unsigned int __thread rand_yield;
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101#endif
102
16aa9ee8 103static CDS_LIST_HEAD(registry);
27b012e2 104
6abb4bd5 105static void mutex_lock(pthread_mutex_t *mutex)
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106{
107 int ret;
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108
109#ifndef DISTRUST_SIGNALS_EXTREME
6abb4bd5 110 ret = pthread_mutex_lock(mutex);
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111 if (ret) {
112 perror("Error in pthread mutex lock");
113 exit(-1);
114 }
09a9f986 115#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
6abb4bd5 116 while ((ret = pthread_mutex_trylock(mutex)) != 0) {
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117 if (ret != EBUSY && ret != EINTR) {
118 printf("ret = %d, errno = %d\n", ret, errno);
119 perror("Error in pthread mutex lock");
120 exit(-1);
121 }
6cf3827c 122 if (CMM_LOAD_SHARED(rcu_reader.need_mb)) {
5481ddb3 123 cmm_smp_mb();
6cf3827c 124 _CMM_STORE_SHARED(rcu_reader.need_mb, 0);
5481ddb3 125 cmm_smp_mb();
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126 }
127 poll(NULL,0,10);
128 }
129#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
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130}
131
6abb4bd5 132static void mutex_unlock(pthread_mutex_t *mutex)
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133{
134 int ret;
135
6abb4bd5 136 ret = pthread_mutex_unlock(mutex);
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137 if (ret) {
138 perror("Error in pthread mutex unlock");
139 exit(-1);
140 }
141}
142
fdf01eed 143#ifdef RCU_MEMBARRIER
25cc6d18 144static void smp_mb_master(int group)
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145{
146 if (likely(has_sys_membarrier))
f0708810 147 membarrier(MEMBARRIER_EXPEDITED);
fdf01eed 148 else
5481ddb3 149 cmm_smp_mb();
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150}
151#endif
152
02be5561 153#ifdef RCU_MB
25cc6d18 154static void smp_mb_master(int group)
40e140c9 155{
5481ddb3 156 cmm_smp_mb();
40e140c9 157}
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158#endif
159
160#ifdef RCU_SIGNAL
78ff9419 161static void force_mb_all_readers(void)
27b012e2 162{
02be5561 163 struct rcu_reader *index;
e3b0cef0 164
27b012e2 165 /*
5481ddb3 166 * Ask for each threads to execute a cmm_smp_mb() so we can consider the
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167 * compiler barriers around rcu read lock as real memory barriers.
168 */
16aa9ee8 169 if (cds_list_empty(&registry))
27b012e2 170 return;
3a86deba 171 /*
5481ddb3 172 * pthread_kill has a cmm_smp_mb(). But beware, we assume it performs
157dca95 173 * a cache flush on architectures with non-coherent cache. Let's play
5481ddb3 174 * safe and don't assume anything : we use cmm_smp_mc() to make sure the
157dca95 175 * cache flush is enforced.
3a86deba 176 */
16aa9ee8 177 cds_list_for_each_entry(index, &registry, node) {
6cf3827c 178 CMM_STORE_SHARED(index->need_mb, 1);
02be5561 179 pthread_kill(index->tid, SIGRCU);
09a9f986 180 }
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181 /*
182 * Wait for sighandler (and thus mb()) to execute on every thread.
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183 *
184 * Note that the pthread_kill() will never be executed on systems
185 * that correctly deliver signals in a timely manner. However, it
186 * is not uncommon for kernels to have bugs that can result in
187 * lost or unduly delayed signals.
188 *
189 * If you are seeing the below pthread_kill() executing much at
190 * all, we suggest testing the underlying kernel and filing the
191 * relevant bug report. For Linux kernels, we recommend getting
192 * the Linux Test Project (LTP).
27b012e2 193 */
16aa9ee8 194 cds_list_for_each_entry(index, &registry, node) {
6cf3827c 195 while (CMM_LOAD_SHARED(index->need_mb)) {
02be5561 196 pthread_kill(index->tid, SIGRCU);
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197 poll(NULL, 0, 1);
198 }
199 }
5481ddb3 200 cmm_smp_mb(); /* read ->need_mb before ending the barrier */
27b012e2 201}
9d7e3f89 202
25cc6d18 203static void smp_mb_master(int group)
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204{
205 force_mb_all_readers();
206}
fdf01eed 207#endif /* #ifdef RCU_SIGNAL */
27b012e2 208
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209/*
210 * synchronize_rcu() waiting. Single thread.
211 */
cfe78e25 212static void wait_gp(void)
bc6c15bb 213{
cfe78e25 214 /* Read reader_gp before read futex */
25cc6d18 215 smp_mb_master(RCU_MB_GROUP);
cfe78e25 216 if (uatomic_read(&gp_futex) == -1)
0854ccff 217 futex_async(&gp_futex, FUTEX_WAIT, -1,
cfe78e25 218 NULL, NULL, 0);
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219}
220
2dfb8b5e 221void update_counter_and_wait(void)
27b012e2 222{
16aa9ee8 223 CDS_LIST_HEAD(qsreaders);
cfe78e25 224 int wait_loops = 0;
02be5561 225 struct rcu_reader *index, *tmp;
27b012e2 226
32c15e4e 227 /* Switch parity: 0 -> 1, 1 -> 0 */
6cf3827c 228 CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
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229
230 /*
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231 * Must commit rcu_gp_ctr update to memory before waiting for quiescent
232 * state. Failure to do so could result in the writer waiting forever
233 * while new readers are always accessing data (no progress). Enforce
234 * compiler-order of store to rcu_gp_ctr before load rcu_reader ctr.
2dfb8b5e 235 */
5481ddb3 236 cmm_barrier();
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237
238 /*
935b11ff 239 *
5481ddb3 240 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
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241 * model easier to understand. It does not have a big performance impact
242 * anyway, given this is the write-side.
243 */
5481ddb3 244 cmm_smp_mb();
2dfb8b5e 245
40e140c9 246 /*
02be5561 247 * Wait for each thread rcu_reader.ctr count to become 0.
27b012e2 248 */
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249 for (;;) {
250 wait_loops++;
251 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
252 uatomic_dec(&gp_futex);
253 /* Write futex before read reader_gp */
25cc6d18 254 smp_mb_master(RCU_MB_GROUP);
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255 }
256
16aa9ee8 257 cds_list_for_each_entry_safe(index, tmp, &registry, node) {
b95a001f 258 if (!rcu_gp_ongoing(&index->ctr))
16aa9ee8 259 cds_list_move(&index->node, &qsreaders);
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260 }
261
e8043c1b 262#ifndef HAS_INCOHERENT_CACHES
16aa9ee8 263 if (cds_list_empty(&registry)) {
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264 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
265 /* Read reader_gp before write futex */
25cc6d18 266 smp_mb_master(RCU_MB_GROUP);
cfe78e25 267 uatomic_set(&gp_futex, 0);
bc6c15bb 268 }
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269 break;
270 } else {
271 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
272 wait_gp();
273 else
06f22bdb 274 caa_cpu_relax();
bc6c15bb 275 }
e8043c1b 276#else /* #ifndef HAS_INCOHERENT_CACHES */
27b012e2 277 /*
40e140c9 278 * BUSY-LOOP. Force the reader thread to commit its
02be5561 279 * rcu_reader.ctr update to memory if we wait for too long.
27b012e2 280 */
16aa9ee8 281 if (cds_list_empty(&registry)) {
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282 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
283 /* Read reader_gp before write futex */
25cc6d18 284 smp_mb_master(RCU_MB_GROUP);
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285 uatomic_set(&gp_futex, 0);
286 }
287 break;
288 } else {
289 switch (wait_loops) {
bc6c15bb 290 case RCU_QS_ACTIVE_ATTEMPTS:
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291 wait_gp();
292 break; /* only escape switch */
bc6c15bb 293 case KICK_READER_LOOPS:
25cc6d18 294 smp_mb_master(RCU_MB_GROUP);
40e140c9 295 wait_loops = 0;
cfe78e25 296 break; /* only escape switch */
bc6c15bb 297 default:
06f22bdb 298 caa_cpu_relax();
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299 }
300 }
e8043c1b 301#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
27b012e2 302 }
cfe78e25 303 /* put back the reader list in the registry */
16aa9ee8 304 cds_list_splice(&qsreaders, &registry);
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305}
306
9598a481 307void synchronize_rcu(void)
2bc59bd7 308{
6abb4bd5 309 mutex_lock(&rcu_gp_lock);
135530fd 310
16aa9ee8 311 if (cds_list_empty(&registry))
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312 goto out;
313
9598a481 314 /* All threads should read qparity before accessing data structure
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315 * where new ptr points to. Must be done within rcu_gp_lock because it
316 * iterates on reader threads.*/
9598a481 317 /* Write new ptr before changing the qparity */
25cc6d18 318 smp_mb_master(RCU_MB_GROUP);
9598a481 319
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320 /*
321 * Wait for previous parity to be empty of readers.
322 */
2dfb8b5e 323 update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */
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324
325 /*
326 * Must finish waiting for quiescent state for parity 0 before
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327 * committing next rcu_gp_ctr update to memory. Failure to do so could
328 * result in the writer waiting forever while new readers are always
329 * accessing data (no progress). Enforce compiler-order of load
330 * rcu_reader ctr before store to rcu_gp_ctr.
9598a481 331 */
5481ddb3 332 cmm_barrier();
9598a481 333
5dba80f9 334 /*
5481ddb3 335 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
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336 * model easier to understand. It does not have a big performance impact
337 * anyway, given this is the write-side.
338 */
5481ddb3 339 cmm_smp_mb();
67c2d80b 340
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341 /*
342 * Wait for previous parity to be empty of readers.
343 */
2dfb8b5e 344 update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */
9598a481 345
9598a481 346 /* Finish waiting for reader threads before letting the old ptr being
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347 * freed. Must be done within rcu_gp_lock because it iterates on reader
348 * threads. */
25cc6d18 349 smp_mb_master(RCU_MB_GROUP);
2dfb8b5e 350out:
6abb4bd5 351 mutex_unlock(&rcu_gp_lock);
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352}
353
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354/*
355 * library wrappers to be used by non-LGPL compatible source code.
356 */
357
358void rcu_read_lock(void)
359{
360 _rcu_read_lock();
361}
362
363void rcu_read_unlock(void)
364{
365 _rcu_read_unlock();
366}
367
121a5d44 368void rcu_register_thread(void)
27b012e2 369{
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370 rcu_reader.tid = pthread_self();
371 assert(rcu_reader.need_mb == 0);
4b5be3be 372 assert(!(rcu_reader.ctr & RCU_GP_CTR_NEST_MASK));
02be5561 373
6abb4bd5 374 mutex_lock(&rcu_gp_lock);
02be5561 375 rcu_init(); /* In case gcc does not support constructor attribute */
16aa9ee8 376 cds_list_add(&rcu_reader.node, &registry);
6abb4bd5 377 mutex_unlock(&rcu_gp_lock);
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378}
379
121a5d44 380void rcu_unregister_thread(void)
27b012e2 381{
6abb4bd5 382 mutex_lock(&rcu_gp_lock);
16aa9ee8 383 cds_list_del(&rcu_reader.node);
6abb4bd5 384 mutex_unlock(&rcu_gp_lock);
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385}
386
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387#ifdef RCU_MEMBARRIER
388void rcu_init(void)
389{
390 if (init_done)
391 return;
392 init_done = 1;
cf5271ee 393 if (!membarrier(MEMBARRIER_EXPEDITED | MEMBARRIER_QUERY))
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394 has_sys_membarrier = 1;
395}
396#endif
397
398#ifdef RCU_SIGNAL
02be5561 399static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context)
27b012e2 400{
40e140c9 401 /*
5481ddb3
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402 * Executing this cmm_smp_mb() is the only purpose of this signal handler.
403 * It punctually promotes cmm_barrier() into cmm_smp_mb() on every thread it is
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404 * executed on.
405 */
5481ddb3 406 cmm_smp_mb();
6cf3827c 407 _CMM_STORE_SHARED(rcu_reader.need_mb, 0);
5481ddb3 408 cmm_smp_mb();
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409}
410
8a5fb4c9 411/*
02be5561 412 * rcu_init constructor. Called when the library is linked, but also when
8a5fb4c9
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413 * reader threads are calling rcu_register_thread().
414 * Should only be called by a single thread at a given time. This is ensured by
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415 * holing the rcu_gp_lock from rcu_register_thread() or by running at library
416 * load time, which should not be executed by multiple threads nor concurrently
417 * with rcu_register_thread() anyway.
8a5fb4c9 418 */
02be5561 419void rcu_init(void)
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420{
421 struct sigaction act;
422 int ret;
423
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424 if (init_done)
425 return;
426 init_done = 1;
427
02be5561 428 act.sa_sigaction = sigrcu_handler;
dd052bd3 429 act.sa_flags = SA_SIGINFO | SA_RESTART;
c297c21c 430 sigemptyset(&act.sa_mask);
02be5561 431 ret = sigaction(SIGRCU, &act, NULL);
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432 if (ret) {
433 perror("Error in sigaction");
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434 exit(-1);
435 }
436}
437
02be5561 438void rcu_exit(void)
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439{
440 struct sigaction act;
441 int ret;
442
02be5561 443 ret = sigaction(SIGRCU, NULL, &act);
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444 if (ret) {
445 perror("Error in sigaction");
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446 exit(-1);
447 }
02be5561 448 assert(act.sa_sigaction == sigrcu_handler);
16aa9ee8 449 assert(cds_list_empty(&registry));
27b012e2 450}
5e77fc1f 451
fdf01eed 452#endif /* #ifdef RCU_SIGNAL */
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453
454#include "urcu-call-rcu-impl.h"
0376e7b2 455#include "urcu-defer-impl.h"
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