Cleanup: Re-organise source dir
[urcu.git] / src / 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
71c811bf 27#define _LGPL_SOURCE
82d50e1a 28#define _DEFAULT_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
999991c6 39#include "urcu/arch.h"
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/* If the headers do not support membarrier system call, fall back on RCU_MB */
67#ifdef __NR_membarrier
68# define membarrier(...) syscall(__NR_membarrier, __VA_ARGS__)
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69#else
70# define membarrier(...) -ENOSYS
71#endif
72
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73enum membarrier_cmd {
74 MEMBARRIER_CMD_QUERY = 0,
75 MEMBARRIER_CMD_SHARED = (1 << 0),
76};
553b7eb9 77
fdf01eed 78#ifdef RCU_MEMBARRIER
834a45ba 79static int init_done;
1de4df4b 80int rcu_has_sys_membarrier;
834a45ba 81
02be5561 82void __attribute__((constructor)) rcu_init(void);
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83#endif
84
85#ifdef RCU_MB
02be5561 86void rcu_init(void)
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87{
88}
89#endif
8a5fb4c9 90
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91#ifdef RCU_SIGNAL
92static int init_done;
93
94void __attribute__((constructor)) rcu_init(void);
95void __attribute__((destructor)) rcu_exit(void);
96#endif
97
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98/*
99 * rcu_gp_lock ensures mutual exclusion between threads calling
100 * synchronize_rcu().
101 */
6abb4bd5 102static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
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103/*
104 * rcu_registry_lock ensures mutual exclusion between threads
105 * registering and unregistering themselves to/from the registry, and
106 * with threads reading that registry from synchronize_rcu(). However,
107 * this lock is not held all the way through the completion of awaiting
108 * for the grace period. It is sporadically released between iterations
109 * on the registry.
110 * rcu_registry_lock may nest inside rcu_gp_lock.
111 */
112static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER;
4de0cd31 113struct rcu_gp rcu_gp = { .ctr = RCU_GP_COUNT };
27b012e2 114
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115/*
116 * Written to only by each individual reader. Read by both the reader and the
117 * writers.
118 */
bd252a04 119DEFINE_URCU_TLS(struct rcu_reader, rcu_reader);
27b012e2 120
16aa9ee8 121static CDS_LIST_HEAD(registry);
27b012e2 122
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123/*
124 * Queue keeping threads awaiting to wait for a grace period. Contains
125 * struct gp_waiters_thread objects.
126 */
127static DEFINE_URCU_WAIT_QUEUE(gp_waiters);
128
6abb4bd5 129static void mutex_lock(pthread_mutex_t *mutex)
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130{
131 int ret;
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132
133#ifndef DISTRUST_SIGNALS_EXTREME
6abb4bd5 134 ret = pthread_mutex_lock(mutex);
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135 if (ret)
136 urcu_die(ret);
09a9f986 137#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
6abb4bd5 138 while ((ret = pthread_mutex_trylock(mutex)) != 0) {
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139 if (ret != EBUSY && ret != EINTR)
140 urcu_die(ret);
bd252a04 141 if (CMM_LOAD_SHARED(URCU_TLS(rcu_reader).need_mb)) {
5481ddb3 142 cmm_smp_mb();
bd252a04 143 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
5481ddb3 144 cmm_smp_mb();
09a9f986 145 }
8999a9ee 146 (void) poll(NULL, 0, 10);
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147 }
148#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
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149}
150
6abb4bd5 151static void mutex_unlock(pthread_mutex_t *mutex)
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152{
153 int ret;
154
6abb4bd5 155 ret = pthread_mutex_unlock(mutex);
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156 if (ret)
157 urcu_die(ret);
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158}
159
fdf01eed 160#ifdef RCU_MEMBARRIER
a4922ed9 161static void smp_mb_master(void)
fdf01eed 162{
1de4df4b 163 if (caa_likely(rcu_has_sys_membarrier))
64f469e6 164 (void) membarrier(MEMBARRIER_CMD_SHARED, 0);
fdf01eed 165 else
5481ddb3 166 cmm_smp_mb();
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167}
168#endif
169
02be5561 170#ifdef RCU_MB
a4922ed9 171static void smp_mb_master(void)
40e140c9 172{
5481ddb3 173 cmm_smp_mb();
40e140c9 174}
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175#endif
176
177#ifdef RCU_SIGNAL
78ff9419 178static void force_mb_all_readers(void)
27b012e2 179{
02be5561 180 struct rcu_reader *index;
e3b0cef0 181
27b012e2 182 /*
5481ddb3 183 * Ask for each threads to execute a cmm_smp_mb() so we can consider the
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184 * compiler barriers around rcu read lock as real memory barriers.
185 */
16aa9ee8 186 if (cds_list_empty(&registry))
27b012e2 187 return;
3a86deba 188 /*
5481ddb3 189 * pthread_kill has a cmm_smp_mb(). But beware, we assume it performs
157dca95 190 * a cache flush on architectures with non-coherent cache. Let's play
5481ddb3 191 * safe and don't assume anything : we use cmm_smp_mc() to make sure the
157dca95 192 * cache flush is enforced.
3a86deba 193 */
16aa9ee8 194 cds_list_for_each_entry(index, &registry, node) {
6cf3827c 195 CMM_STORE_SHARED(index->need_mb, 1);
02be5561 196 pthread_kill(index->tid, SIGRCU);
09a9f986 197 }
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198 /*
199 * Wait for sighandler (and thus mb()) to execute on every thread.
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200 *
201 * Note that the pthread_kill() will never be executed on systems
202 * that correctly deliver signals in a timely manner. However, it
203 * is not uncommon for kernels to have bugs that can result in
204 * lost or unduly delayed signals.
205 *
206 * If you are seeing the below pthread_kill() executing much at
207 * all, we suggest testing the underlying kernel and filing the
208 * relevant bug report. For Linux kernels, we recommend getting
209 * the Linux Test Project (LTP).
27b012e2 210 */
16aa9ee8 211 cds_list_for_each_entry(index, &registry, node) {
6cf3827c 212 while (CMM_LOAD_SHARED(index->need_mb)) {
02be5561 213 pthread_kill(index->tid, SIGRCU);
8999a9ee 214 (void) poll(NULL, 0, 1);
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215 }
216 }
5481ddb3 217 cmm_smp_mb(); /* read ->need_mb before ending the barrier */
27b012e2 218}
9d7e3f89 219
a4922ed9 220static void smp_mb_master(void)
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221{
222 force_mb_all_readers();
223}
fdf01eed 224#endif /* #ifdef RCU_SIGNAL */
27b012e2 225
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226/*
227 * synchronize_rcu() waiting. Single thread.
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228 * Always called with rcu_registry lock held. Releases this lock and
229 * grabs it again. Holds the lock when it returns.
bc6c15bb 230 */
cfe78e25 231static void wait_gp(void)
bc6c15bb 232{
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233 /*
234 * Read reader_gp before read futex. smp_mb_master() needs to
235 * be called with the rcu registry lock held in RCU_SIGNAL
236 * flavor.
237 */
a4922ed9 238 smp_mb_master();
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239 /* Temporarily unlock the registry lock. */
240 mutex_unlock(&rcu_registry_lock);
b0a841b4 241 if (uatomic_read(&rcu_gp.futex) != -1)
fca9fb96 242 goto end;
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243 while (futex_async(&rcu_gp.futex, FUTEX_WAIT, -1,
244 NULL, NULL, 0)) {
245 switch (errno) {
246 case EWOULDBLOCK:
247 /* Value already changed. */
fca9fb96 248 goto end;
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249 case EINTR:
250 /* Retry if interrupted by signal. */
251 break; /* Get out of switch. */
252 default:
253 /* Unexpected error. */
254 urcu_die(errno);
255 }
256 }
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257end:
258 /*
259 * Re-lock the registry lock before the next loop.
260 */
261 mutex_lock(&rcu_registry_lock);
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262}
263
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264/*
265 * Always called with rcu_registry lock held. Releases this lock between
266 * iterations and grabs it again. Holds the lock when it returns.
267 */
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268static void wait_for_readers(struct cds_list_head *input_readers,
269 struct cds_list_head *cur_snap_readers,
270 struct cds_list_head *qsreaders)
27b012e2 271{
9340c38d 272 unsigned int wait_loops = 0;
02be5561 273 struct rcu_reader *index, *tmp;
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274#ifdef HAS_INCOHERENT_CACHES
275 unsigned int wait_gp_loops = 0;
276#endif /* HAS_INCOHERENT_CACHES */
27b012e2 277
40e140c9 278 /*
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279 * Wait for each thread URCU_TLS(rcu_reader).ctr to either
280 * indicate quiescence (not nested), or observe the current
ed1b099e 281 * rcu_gp.ctr value.
27b012e2 282 */
cfe78e25 283 for (;;) {
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284 if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
285 wait_loops++;
9340c38d 286 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
ed1b099e 287 uatomic_dec(&rcu_gp.futex);
cfe78e25 288 /* Write futex before read reader_gp */
a4922ed9 289 smp_mb_master();
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290 }
291
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292 cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
293 switch (rcu_reader_state(&index->ctr)) {
294 case RCU_READER_ACTIVE_CURRENT:
295 if (cur_snap_readers) {
296 cds_list_move(&index->node,
297 cur_snap_readers);
298 break;
299 }
300 /* Fall-through */
301 case RCU_READER_INACTIVE:
302 cds_list_move(&index->node, qsreaders);
303 break;
304 case RCU_READER_ACTIVE_OLD:
305 /*
306 * Old snapshot. Leaving node in
307 * input_readers will make us busy-loop
308 * until the snapshot becomes current or
309 * the reader becomes inactive.
310 */
311 break;
312 }
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313 }
314
e8043c1b 315#ifndef HAS_INCOHERENT_CACHES
fd189fa5 316 if (cds_list_empty(input_readers)) {
9340c38d 317 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
cfe78e25 318 /* Read reader_gp before write futex */
a4922ed9 319 smp_mb_master();
ed1b099e 320 uatomic_set(&rcu_gp.futex, 0);
bc6c15bb 321 }
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322 break;
323 } else {
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324 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
325 /* wait_gp unlocks/locks registry lock. */
cfe78e25 326 wait_gp();
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327 } else {
328 /* Temporarily unlock the registry lock. */
329 mutex_unlock(&rcu_registry_lock);
06f22bdb 330 caa_cpu_relax();
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331 /*
332 * Re-lock the registry lock before the
333 * next loop.
334 */
335 mutex_lock(&rcu_registry_lock);
336 }
bc6c15bb 337 }
e8043c1b 338#else /* #ifndef HAS_INCOHERENT_CACHES */
27b012e2 339 /*
40e140c9 340 * BUSY-LOOP. Force the reader thread to commit its
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341 * URCU_TLS(rcu_reader).ctr update to memory if we wait
342 * for too long.
27b012e2 343 */
fd189fa5 344 if (cds_list_empty(input_readers)) {
9340c38d 345 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
cfe78e25 346 /* Read reader_gp before write futex */
a4922ed9 347 smp_mb_master();
ed1b099e 348 uatomic_set(&rcu_gp.futex, 0);
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349 }
350 break;
351 } else {
9340c38d 352 if (wait_gp_loops == KICK_READER_LOOPS) {
a4922ed9 353 smp_mb_master();
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354 wait_gp_loops = 0;
355 }
356 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
fca9fb96 357 /* wait_gp unlocks/locks registry lock. */
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358 wait_gp();
359 wait_gp_loops++;
360 } else {
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361 /* Temporarily unlock the registry lock. */
362 mutex_unlock(&rcu_registry_lock);
06f22bdb 363 caa_cpu_relax();
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364 /*
365 * Re-lock the registry lock before the
366 * next loop.
367 */
368 mutex_lock(&rcu_registry_lock);
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369 }
370 }
e8043c1b 371#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
27b012e2 372 }
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373}
374
9598a481 375void synchronize_rcu(void)
2bc59bd7 376{
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377 CDS_LIST_HEAD(cur_snap_readers);
378 CDS_LIST_HEAD(qsreaders);
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379 DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
380 struct urcu_waiters waiters;
381
382 /*
383 * Add ourself to gp_waiters queue of threads awaiting to wait
384 * for a grace period. Proceed to perform the grace period only
385 * if we are the first thread added into the queue.
386 * The implicit memory barrier before urcu_wait_add()
387 * orders prior memory accesses of threads put into the wait
388 * queue before their insertion into the wait queue.
389 */
390 if (urcu_wait_add(&gp_waiters, &wait) != 0) {
391 /* Not first in queue: will be awakened by another thread. */
392 urcu_adaptative_busy_wait(&wait);
393 /* Order following memory accesses after grace period. */
394 cmm_smp_mb();
395 return;
396 }
397 /* We won't need to wake ourself up */
398 urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);
fd189fa5 399
6abb4bd5 400 mutex_lock(&rcu_gp_lock);
135530fd 401
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402 /*
403 * Move all waiters into our local queue.
404 */
405 urcu_move_waiters(&waiters, &gp_waiters);
406
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407 mutex_lock(&rcu_registry_lock);
408
16aa9ee8 409 if (cds_list_empty(&registry))
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410 goto out;
411
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412 /*
413 * All threads should read qparity before accessing data structure
414 * where new ptr points to. Must be done within rcu_registry_lock
415 * because it iterates on reader threads.
416 */
9598a481 417 /* Write new ptr before changing the qparity */
a4922ed9 418 smp_mb_master();
9598a481 419
9598a481 420 /*
c9488684 421 * Wait for readers to observe original parity or be quiescent.
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422 * wait_for_readers() can release and grab again rcu_registry_lock
423 * interally.
9598a481 424 */
fd189fa5 425 wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
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426
427 /*
c9488684 428 * Must finish waiting for quiescent state for original parity before
ed1b099e 429 * committing next rcu_gp.ctr update to memory. Failure to do so could
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430 * result in the writer waiting forever while new readers are always
431 * accessing data (no progress). Enforce compiler-order of load
ed1b099e 432 * URCU_TLS(rcu_reader).ctr before store to rcu_gp.ctr.
9598a481 433 */
5481ddb3 434 cmm_barrier();
9598a481 435
5dba80f9 436 /*
5481ddb3 437 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
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438 * model easier to understand. It does not have a big performance impact
439 * anyway, given this is the write-side.
440 */
5481ddb3 441 cmm_smp_mb();
67c2d80b 442
c9488684 443 /* Switch parity: 0 -> 1, 1 -> 0 */
ed1b099e 444 CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR_PHASE);
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445
446 /*
ed1b099e 447 * Must commit rcu_gp.ctr update to memory before waiting for quiescent
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448 * state. Failure to do so could result in the writer waiting forever
449 * while new readers are always accessing data (no progress). Enforce
ed1b099e 450 * compiler-order of store to rcu_gp.ctr before load rcu_reader ctr.
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451 */
452 cmm_barrier();
453
454 /*
455 *
456 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
457 * model easier to understand. It does not have a big performance impact
458 * anyway, given this is the write-side.
459 */
460 cmm_smp_mb();
461
9598a481 462 /*
c9488684 463 * Wait for readers to observe new parity or be quiescent.
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464 * wait_for_readers() can release and grab again rcu_registry_lock
465 * interally.
9598a481 466 */
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467 wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
468
469 /*
470 * Put quiescent reader list back into registry.
471 */
472 cds_list_splice(&qsreaders, &registry);
9598a481 473
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474 /*
475 * Finish waiting for reader threads before letting the old ptr
476 * being freed. Must be done within rcu_registry_lock because it
477 * iterates on reader threads.
478 */
a4922ed9 479 smp_mb_master();
2dfb8b5e 480out:
731ccb96 481 mutex_unlock(&rcu_registry_lock);
6abb4bd5 482 mutex_unlock(&rcu_gp_lock);
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483
484 /*
485 * Wakeup waiters only after we have completed the grace period
486 * and have ensured the memory barriers at the end of the grace
487 * period have been issued.
488 */
489 urcu_wake_all_waiters(&waiters);
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490}
491
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492/*
493 * library wrappers to be used by non-LGPL compatible source code.
494 */
495
496void rcu_read_lock(void)
497{
498 _rcu_read_lock();
499}
500
501void rcu_read_unlock(void)
502{
503 _rcu_read_unlock();
504}
505
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506int rcu_read_ongoing(void)
507{
508 return _rcu_read_ongoing();
509}
510
121a5d44 511void rcu_register_thread(void)
27b012e2 512{
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513 URCU_TLS(rcu_reader).tid = pthread_self();
514 assert(URCU_TLS(rcu_reader).need_mb == 0);
515 assert(!(URCU_TLS(rcu_reader).ctr & RCU_GP_CTR_NEST_MASK));
02be5561 516
731ccb96 517 mutex_lock(&rcu_registry_lock);
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518 assert(!URCU_TLS(rcu_reader).registered);
519 URCU_TLS(rcu_reader).registered = 1;
02be5561 520 rcu_init(); /* In case gcc does not support constructor attribute */
bd252a04 521 cds_list_add(&URCU_TLS(rcu_reader).node, &registry);
731ccb96 522 mutex_unlock(&rcu_registry_lock);
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523}
524
121a5d44 525void rcu_unregister_thread(void)
27b012e2 526{
731ccb96 527 mutex_lock(&rcu_registry_lock);
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528 assert(URCU_TLS(rcu_reader).registered);
529 URCU_TLS(rcu_reader).registered = 0;
bd252a04 530 cds_list_del(&URCU_TLS(rcu_reader).node);
731ccb96 531 mutex_unlock(&rcu_registry_lock);
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532}
533
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534#ifdef RCU_MEMBARRIER
535void rcu_init(void)
536{
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537 int ret;
538
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539 if (init_done)
540 return;
541 init_done = 1;
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542 ret = membarrier(MEMBARRIER_CMD_QUERY, 0);
543 if (ret >= 0 && (ret & MEMBARRIER_CMD_SHARED)) {
1de4df4b 544 rcu_has_sys_membarrier = 1;
64f469e6 545 }
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546}
547#endif
548
549#ifdef RCU_SIGNAL
02be5561 550static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context)
27b012e2 551{
40e140c9 552 /*
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553 * Executing this cmm_smp_mb() is the only purpose of this signal handler.
554 * It punctually promotes cmm_barrier() into cmm_smp_mb() on every thread it is
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555 * executed on.
556 */
5481ddb3 557 cmm_smp_mb();
bd252a04 558 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
5481ddb3 559 cmm_smp_mb();
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560}
561
8a5fb4c9 562/*
02be5561 563 * rcu_init constructor. Called when the library is linked, but also when
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564 * reader threads are calling rcu_register_thread().
565 * Should only be called by a single thread at a given time. This is ensured by
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566 * holing the rcu_registry_lock from rcu_register_thread() or by running
567 * at library load time, which should not be executed by multiple
568 * threads nor concurrently with rcu_register_thread() anyway.
8a5fb4c9 569 */
02be5561 570void rcu_init(void)
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571{
572 struct sigaction act;
573 int ret;
574
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575 if (init_done)
576 return;
577 init_done = 1;
578
02be5561 579 act.sa_sigaction = sigrcu_handler;
dd052bd3 580 act.sa_flags = SA_SIGINFO | SA_RESTART;
c297c21c 581 sigemptyset(&act.sa_mask);
02be5561 582 ret = sigaction(SIGRCU, &act, NULL);
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583 if (ret)
584 urcu_die(errno);
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585}
586
02be5561 587void rcu_exit(void)
27b012e2 588{
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589 /*
590 * Don't unregister the SIGRCU signal handler anymore, because
591 * call_rcu threads could still be using it shortly before the
592 * application exits.
593 * Assertion disabled because call_rcu threads are now rcu
594 * readers, and left running at exit.
595 * assert(cds_list_empty(&registry));
596 */
27b012e2 597}
5e77fc1f 598
fdf01eed 599#endif /* #ifdef RCU_SIGNAL */
5e77fc1f 600
5e6b23a6 601DEFINE_RCU_FLAVOR(rcu_flavor);
541d828d 602
5e77fc1f 603#include "urcu-call-rcu-impl.h"
0376e7b2 604#include "urcu-defer-impl.h"
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