src/urcu.c

   1 /*
   2  * urcu.c
   3  *
   4  * Userspace RCU library
   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 URCU_NO_COMPAT_IDENTIFIERS
  27 #define _BSD_SOURCE
  28 #define _LGPL_SOURCE
  29 #define _DEFAULT_SOURCE
  30 #include <stdio.h>
  31 #include <pthread.h>
  32 #include <signal.h>
  33 #include <assert.h>
  34 #include <stdlib.h>
  35 #include <stdint.h>
  36 #include <string.h>
  37 #include <errno.h>
  38 #include <stdbool.h>
  39 #include <poll.h>
  40
  41 #include <urcu/config.h>
  42 #include <urcu/arch.h>
  43 #include <urcu/wfcqueue.h>
  44 #include <urcu/map/urcu.h>
  45 #include <urcu/static/urcu.h>
  46 #include <urcu/pointer.h>
  47 #include <urcu/tls-compat.h>
  48
  49 #include "urcu-die.h"
  50 #include "urcu-wait.h"
  51 #include "urcu-utils.h"
  52
  53 #define URCU_API_MAP
  54 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
  55 #undef _LGPL_SOURCE
  56 #include <urcu/urcu.h>
  57 #define _LGPL_SOURCE
  58
  59 /*
  60  * If a reader is really non-cooperative and refuses to commit its
  61  * rcu_active_readers count to memory (there is no barrier in the reader
  62  * per-se), kick it after 10 loops waiting for it.
  63  */
  64 #define KICK_READER_LOOPS       10
  65
  66 /*
  67  * Active attempts to check for reader Q.S. before calling futex().
  68  */
  69 #define RCU_QS_ACTIVE_ATTEMPTS 100
  70
  71 /* If the headers do not support membarrier system call, fall back on RCU_MB */
  72 #ifdef __NR_membarrier
  73 # define membarrier(...)                syscall(__NR_membarrier, __VA_ARGS__)
  74 #else
  75 # define membarrier(...)                -ENOSYS
  76 #endif
  77
  78 enum membarrier_cmd {
  79         MEMBARRIER_CMD_QUERY                            = 0,
  80         MEMBARRIER_CMD_SHARED                           = (1 << 0),
  81         /* reserved for MEMBARRIER_CMD_SHARED_EXPEDITED (1 << 1) */
  82         /* reserved for MEMBARRIER_CMD_PRIVATE (1 << 2) */
  83         MEMBARRIER_CMD_PRIVATE_EXPEDITED                = (1 << 3),
  84         MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED       = (1 << 4),
  85 };
  86
  87 #ifdef RCU_MEMBARRIER
  88 static int init_done;
  89 static int urcu_memb_has_sys_membarrier_private_expedited;
  90
  91 #ifndef CONFIG_RCU_FORCE_SYS_MEMBARRIER
  92 /*
  93  * Explicitly initialize to zero because we can't alias a non-static
  94  * uninitialized variable.
  95  */
  96 int urcu_memb_has_sys_membarrier = 0;
  97 URCU_ATTR_ALIAS("urcu_memb_has_sys_membarrier")
  98 extern int rcu_has_sys_membarrier_memb;
  99 #endif
 100
 101 void __attribute__((constructor)) rcu_init(void);
 102 #endif
 103
 104 #ifdef RCU_MB
 105 void rcu_init(void)
 106 {
 107 }
 108 URCU_ATTR_ALIAS(urcu_stringify(rcu_init))
 109 void alias_rcu_init(void);
 110 #endif
 111
 112 #ifdef RCU_SIGNAL
 113 static int init_done;
 114
 115 void __attribute__((constructor)) rcu_init(void);
 116 void __attribute__((destructor)) rcu_exit(void);
 117 #endif
 118
 119 /*
 120  * rcu_gp_lock ensures mutual exclusion between threads calling
 121  * synchronize_rcu().
 122  */
 123 static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
 124 /*
 125  * rcu_registry_lock ensures mutual exclusion between threads
 126  * registering and unregistering themselves to/from the registry, and
 127  * with threads reading that registry from synchronize_rcu(). However,
 128  * this lock is not held all the way through the completion of awaiting
 129  * for the grace period. It is sporadically released between iterations
 130  * on the registry.
 131  * rcu_registry_lock may nest inside rcu_gp_lock.
 132  */
 133 static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER;
 134 struct urcu_gp rcu_gp = { .ctr = URCU_GP_COUNT };
 135 URCU_ATTR_ALIAS(urcu_stringify(rcu_gp))
 136 extern struct urcu_gp alias_rcu_gp;
 137
 138 /*
 139  * Written to only by each individual reader. Read by both the reader and the
 140  * writers.
 141  */
 142 DEFINE_URCU_TLS(struct urcu_reader, rcu_reader);
 143 DEFINE_URCU_TLS_ALIAS(struct urcu_reader, rcu_reader, alias_rcu_reader);
 144
 145 static CDS_LIST_HEAD(registry);
 146
 147 /*
 148  * Queue keeping threads awaiting to wait for a grace period. Contains
 149  * struct gp_waiters_thread objects.
 150  */
 151 static DEFINE_URCU_WAIT_QUEUE(gp_waiters);
 152
 153 static void mutex_lock(pthread_mutex_t *mutex)
 154 {
 155         int ret;
 156
 157 #ifndef DISTRUST_SIGNALS_EXTREME
 158         ret = pthread_mutex_lock(mutex);
 159         if (ret)
 160                 urcu_die(ret);
 161 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
 162         while ((ret = pthread_mutex_trylock(mutex)) != 0) {
 163                 if (ret != EBUSY && ret != EINTR)
 164                         urcu_die(ret);
 165                 if (CMM_LOAD_SHARED(URCU_TLS(rcu_reader).need_mb)) {
 166                         cmm_smp_mb();
 167                         _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
 168                         cmm_smp_mb();
 169                 }
 170                 (void) poll(NULL, 0, 10);
 171         }
 172 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
 173 }
 174
 175 static void mutex_unlock(pthread_mutex_t *mutex)
 176 {
 177         int ret;
 178
 179         ret = pthread_mutex_unlock(mutex);
 180         if (ret)
 181                 urcu_die(ret);
 182 }
 183
 184 #ifdef RCU_MEMBARRIER
 185 static void smp_mb_master(void)
 186 {
 187         if (caa_likely(urcu_memb_has_sys_membarrier)) {
 188                 if (membarrier(urcu_memb_has_sys_membarrier_private_expedited ?
 189                                 MEMBARRIER_CMD_PRIVATE_EXPEDITED :
 190                                 MEMBARRIER_CMD_SHARED, 0))
 191                         urcu_die(errno);
 192         } else {
 193                 cmm_smp_mb();
 194         }
 195 }
 196 #endif
 197
 198 #ifdef RCU_MB
 199 static void smp_mb_master(void)
 200 {
 201         cmm_smp_mb();
 202 }
 203 #endif
 204
 205 #ifdef RCU_SIGNAL
 206 static void force_mb_all_readers(void)
 207 {
 208         struct urcu_reader *index;
 209
 210         /*
 211          * Ask for each threads to execute a cmm_smp_mb() so we can consider the
 212          * compiler barriers around rcu read lock as real memory barriers.
 213          */
 214         if (cds_list_empty(&registry))
 215                 return;
 216         /*
 217          * pthread_kill has a cmm_smp_mb(). But beware, we assume it performs
 218          * a cache flush on architectures with non-coherent cache. Let's play
 219          * safe and don't assume anything : we use cmm_smp_mc() to make sure the
 220          * cache flush is enforced.
 221          */
 222         cds_list_for_each_entry(index, &registry, node) {
 223                 CMM_STORE_SHARED(index->need_mb, 1);
 224                 pthread_kill(index->tid, SIGRCU);
 225         }
 226         /*
 227          * Wait for sighandler (and thus mb()) to execute on every thread.
 228          *
 229          * Note that the pthread_kill() will never be executed on systems
 230          * that correctly deliver signals in a timely manner.  However, it
 231          * is not uncommon for kernels to have bugs that can result in
 232          * lost or unduly delayed signals.
 233          *
 234          * If you are seeing the below pthread_kill() executing much at
 235          * all, we suggest testing the underlying kernel and filing the
 236          * relevant bug report.  For Linux kernels, we recommend getting
 237          * the Linux Test Project (LTP).
 238          */
 239         cds_list_for_each_entry(index, &registry, node) {
 240                 while (CMM_LOAD_SHARED(index->need_mb)) {
 241                         pthread_kill(index->tid, SIGRCU);
 242                         (void) poll(NULL, 0, 1);
 243                 }
 244         }
 245         cmm_smp_mb();   /* read ->need_mb before ending the barrier */
 246 }
 247
 248 static void smp_mb_master(void)
 249 {
 250         force_mb_all_readers();
 251 }
 252 #endif /* #ifdef RCU_SIGNAL */
 253
 254 /*
 255  * synchronize_rcu() waiting. Single thread.
 256  * Always called with rcu_registry lock held. Releases this lock and
 257  * grabs it again. Holds the lock when it returns.
 258  */
 259 static void wait_gp(void)
 260 {
 261         /*
 262          * Read reader_gp before read futex. smp_mb_master() needs to
 263          * be called with the rcu registry lock held in RCU_SIGNAL
 264          * flavor.
 265          */
 266         smp_mb_master();
 267         /* Temporarily unlock the registry lock. */
 268         mutex_unlock(&rcu_registry_lock);
 269         while (uatomic_read(&rcu_gp.futex) == -1) {
 270                 if (!futex_async(&rcu_gp.futex, FUTEX_WAIT, -1, NULL, NULL, 0)) {
 271                         /*
 272                          * Prior queued wakeups queued by unrelated code
 273                          * using the same address can cause futex wait to
 274                          * return 0 even through the futex value is still
 275                          * -1 (spurious wakeups). Check the value again
 276                          * in user-space to validate whether it really
 277                          * differs from -1.
 278                          */
 279                         continue;
 280                 }
 281                 switch (errno) {
 282                 case EAGAIN:
 283                         /* Value already changed. */
 284                         goto end;
 285                 case EINTR:
 286                         /* Retry if interrupted by signal. */
 287                         break;  /* Get out of switch. Check again. */
 288                 default:
 289                         /* Unexpected error. */
 290                         urcu_die(errno);
 291                 }
 292         }
 293 end:
 294         /*
 295          * Re-lock the registry lock before the next loop.
 296          */
 297         mutex_lock(&rcu_registry_lock);
 298 }
 299
 300 /*
 301  * Always called with rcu_registry lock held. Releases this lock between
 302  * iterations and grabs it again. Holds the lock when it returns.
 303  */
 304 static void wait_for_readers(struct cds_list_head *input_readers,
 305                         struct cds_list_head *cur_snap_readers,
 306                         struct cds_list_head *qsreaders)
 307 {
 308         unsigned int wait_loops = 0;
 309         struct urcu_reader *index, *tmp;
 310 #ifdef HAS_INCOHERENT_CACHES
 311         unsigned int wait_gp_loops = 0;
 312 #endif /* HAS_INCOHERENT_CACHES */
 313
 314         /*
 315          * Wait for each thread URCU_TLS(rcu_reader).ctr to either
 316          * indicate quiescence (not nested), or observe the current
 317          * rcu_gp.ctr value.
 318          */
 319         for (;;) {
 320                 if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
 321                         wait_loops++;
 322                 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
 323                         uatomic_dec(&rcu_gp.futex);
 324                         /* Write futex before read reader_gp */
 325                         smp_mb_master();
 326                 }
 327
 328                 cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
 329                         switch (urcu_common_reader_state(&rcu_gp, &index->ctr)) {
 330                         case URCU_READER_ACTIVE_CURRENT:
 331                                 if (cur_snap_readers) {
 332                                         cds_list_move(&index->node,
 333                                                 cur_snap_readers);
 334                                         break;
 335                                 }
 336                                 /* Fall-through */
 337                         case URCU_READER_INACTIVE:
 338                                 cds_list_move(&index->node, qsreaders);
 339                                 break;
 340                         case URCU_READER_ACTIVE_OLD:
 341                                 /*
 342                                  * Old snapshot. Leaving node in
 343                                  * input_readers will make us busy-loop
 344                                  * until the snapshot becomes current or
 345                                  * the reader becomes inactive.
 346                                  */
 347                                 break;
 348                         }
 349                 }
 350
 351 #ifndef HAS_INCOHERENT_CACHES
 352                 if (cds_list_empty(input_readers)) {
 353                         if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
 354                                 /* Read reader_gp before write futex */
 355                                 smp_mb_master();
 356                                 uatomic_set(&rcu_gp.futex, 0);
 357                         }
 358                         break;
 359                 } else {
 360                         if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
 361                                 /* wait_gp unlocks/locks registry lock. */
 362                                 wait_gp();
 363                         } else {
 364                                 /* Temporarily unlock the registry lock. */
 365                                 mutex_unlock(&rcu_registry_lock);
 366                                 caa_cpu_relax();
 367                                 /*
 368                                  * Re-lock the registry lock before the
 369                                  * next loop.
 370                                  */
 371                                 mutex_lock(&rcu_registry_lock);
 372                         }
 373                 }
 374 #else /* #ifndef HAS_INCOHERENT_CACHES */
 375                 /*
 376                  * BUSY-LOOP. Force the reader thread to commit its
 377                  * URCU_TLS(rcu_reader).ctr update to memory if we wait
 378                  * for too long.
 379                  */
 380                 if (cds_list_empty(input_readers)) {
 381                         if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
 382                                 /* Read reader_gp before write futex */
 383                                 smp_mb_master();
 384                                 uatomic_set(&rcu_gp.futex, 0);
 385                         }
 386                         break;
 387                 } else {
 388                         if (wait_gp_loops == KICK_READER_LOOPS) {
 389                                 smp_mb_master();
 390                                 wait_gp_loops = 0;
 391                         }
 392                         if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
 393                                 /* wait_gp unlocks/locks registry lock. */
 394                                 wait_gp();
 395                                 wait_gp_loops++;
 396                         } else {
 397                                 /* Temporarily unlock the registry lock. */
 398                                 mutex_unlock(&rcu_registry_lock);
 399                                 caa_cpu_relax();
 400                                 /*
 401                                  * Re-lock the registry lock before the
 402                                  * next loop.
 403                                  */
 404                                 mutex_lock(&rcu_registry_lock);
 405                         }
 406                 }
 407 #endif /* #else #ifndef HAS_INCOHERENT_CACHES */
 408         }
 409 }
 410
 411 void synchronize_rcu(void)
 412 {
 413         CDS_LIST_HEAD(cur_snap_readers);
 414         CDS_LIST_HEAD(qsreaders);
 415         DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
 416         struct urcu_waiters waiters;
 417
 418         /*
 419          * Add ourself to gp_waiters queue of threads awaiting to wait
 420          * for a grace period. Proceed to perform the grace period only
 421          * if we are the first thread added into the queue.
 422          * The implicit memory barrier before urcu_wait_add()
 423          * orders prior memory accesses of threads put into the wait
 424          * queue before their insertion into the wait queue.
 425          */
 426         if (urcu_wait_add(&gp_waiters, &wait) != 0) {
 427                 /* Not first in queue: will be awakened by another thread. */
 428                 urcu_adaptative_busy_wait(&wait);
 429                 /* Order following memory accesses after grace period. */
 430                 cmm_smp_mb();
 431                 return;
 432         }
 433         /* We won't need to wake ourself up */
 434         urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);
 435
 436         mutex_lock(&rcu_gp_lock);
 437
 438         /*
 439          * Move all waiters into our local queue.
 440          */
 441         urcu_move_waiters(&waiters, &gp_waiters);
 442
 443         mutex_lock(&rcu_registry_lock);
 444
 445         if (cds_list_empty(&registry))
 446                 goto out;
 447
 448         /*
 449          * All threads should read qparity before accessing data structure
 450          * where new ptr points to. Must be done within rcu_registry_lock
 451          * because it iterates on reader threads.
 452          */
 453         /* Write new ptr before changing the qparity */
 454         smp_mb_master();
 455
 456         /*
 457          * Wait for readers to observe original parity or be quiescent.
 458          * wait_for_readers() can release and grab again rcu_registry_lock
 459          * interally.
 460          */
 461         wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
 462
 463         /*
 464          * Must finish waiting for quiescent state for original parity before
 465          * committing next rcu_gp.ctr update to memory. Failure to do so could
 466          * result in the writer waiting forever while new readers are always
 467          * accessing data (no progress).  Enforce compiler-order of load
 468          * URCU_TLS(rcu_reader).ctr before store to rcu_gp.ctr.
 469          */
 470         cmm_barrier();
 471
 472         /*
 473          * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
 474          * model easier to understand. It does not have a big performance impact
 475          * anyway, given this is the write-side.
 476          */
 477         cmm_smp_mb();
 478
 479         /* Switch parity: 0 -> 1, 1 -> 0 */
 480         CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ URCU_GP_CTR_PHASE);
 481
 482         /*
 483          * Must commit rcu_gp.ctr update to memory before waiting for quiescent
 484          * state. Failure to do so could result in the writer waiting forever
 485          * while new readers are always accessing data (no progress). Enforce
 486          * compiler-order of store to rcu_gp.ctr before load rcu_reader ctr.
 487          */
 488         cmm_barrier();
 489
 490         /*
 491          *
 492          * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
 493          * model easier to understand. It does not have a big performance impact
 494          * anyway, given this is the write-side.
 495          */
 496         cmm_smp_mb();
 497
 498         /*
 499          * Wait for readers to observe new parity or be quiescent.
 500          * wait_for_readers() can release and grab again rcu_registry_lock
 501          * interally.
 502          */
 503         wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
 504
 505         /*
 506          * Put quiescent reader list back into registry.
 507          */
 508         cds_list_splice(&qsreaders, &registry);
 509
 510         /*
 511          * Finish waiting for reader threads before letting the old ptr
 512          * being freed. Must be done within rcu_registry_lock because it
 513          * iterates on reader threads.
 514          */
 515         smp_mb_master();
 516 out:
 517         mutex_unlock(&rcu_registry_lock);
 518         mutex_unlock(&rcu_gp_lock);
 519
 520         /*
 521          * Wakeup waiters only after we have completed the grace period
 522          * and have ensured the memory barriers at the end of the grace
 523          * period have been issued.
 524          */
 525         urcu_wake_all_waiters(&waiters);
 526 }
 527 URCU_ATTR_ALIAS(urcu_stringify(synchronize_rcu))
 528 void alias_synchronize_rcu();
 529
 530 /*
 531  * library wrappers to be used by non-LGPL compatible source code.
 532  */
 533
 534 void rcu_read_lock(void)
 535 {
 536         _rcu_read_lock();
 537 }
 538 URCU_ATTR_ALIAS(urcu_stringify(rcu_read_lock))
 539 void alias_rcu_read_lock();
 540
 541 void rcu_read_unlock(void)
 542 {
 543         _rcu_read_unlock();
 544 }
 545 URCU_ATTR_ALIAS(urcu_stringify(rcu_read_unlock))
 546 void alias_rcu_read_unlock();
 547
 548 int rcu_read_ongoing(void)
 549 {
 550         return _rcu_read_ongoing();
 551 }
 552 URCU_ATTR_ALIAS(urcu_stringify(rcu_read_ongoing))
 553 void alias_rcu_read_ongoing();
 554
 555 void rcu_register_thread(void)
 556 {
 557         URCU_TLS(rcu_reader).tid = pthread_self();
 558         assert(URCU_TLS(rcu_reader).need_mb == 0);
 559         assert(!(URCU_TLS(rcu_reader).ctr & URCU_GP_CTR_NEST_MASK));
 560
 561         mutex_lock(&rcu_registry_lock);
 562         assert(!URCU_TLS(rcu_reader).registered);
 563         URCU_TLS(rcu_reader).registered = 1;
 564         rcu_init();     /* In case gcc does not support constructor attribute */
 565         cds_list_add(&URCU_TLS(rcu_reader).node, &registry);
 566         mutex_unlock(&rcu_registry_lock);
 567 }
 568 URCU_ATTR_ALIAS(urcu_stringify(rcu_register_thread))
 569 void alias_rcu_register_thread();
 570
 571 void rcu_unregister_thread(void)
 572 {
 573         mutex_lock(&rcu_registry_lock);
 574         assert(URCU_TLS(rcu_reader).registered);
 575         URCU_TLS(rcu_reader).registered = 0;
 576         cds_list_del(&URCU_TLS(rcu_reader).node);
 577         mutex_unlock(&rcu_registry_lock);
 578 }
 579 URCU_ATTR_ALIAS(urcu_stringify(rcu_unregister_thread))
 580 void alias_rcu_unregister_thread();
 581
 582 #ifdef RCU_MEMBARRIER
 583
 584 #ifdef CONFIG_RCU_FORCE_SYS_MEMBARRIER
 585 static
 586 void rcu_sys_membarrier_status(bool available)
 587 {
 588         if (!available)
 589                 abort();
 590 }
 591 #else
 592 static
 593 void rcu_sys_membarrier_status(bool available)
 594 {
 595         if (!available)
 596                 return;
 597         urcu_memb_has_sys_membarrier = 1;
 598 }
 599 #endif
 600
 601 static
 602 void rcu_sys_membarrier_init(void)
 603 {
 604         bool available = false;
 605         int mask;
 606
 607         mask = membarrier(MEMBARRIER_CMD_QUERY, 0);
 608         if (mask >= 0) {
 609                 if (mask & MEMBARRIER_CMD_PRIVATE_EXPEDITED) {
 610                         if (membarrier(MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED, 0))
 611                                 urcu_die(errno);
 612                         urcu_memb_has_sys_membarrier_private_expedited = 1;
 613                         available = true;
 614                 } else if (mask & MEMBARRIER_CMD_SHARED) {
 615                         available = true;
 616                 }
 617         }
 618         rcu_sys_membarrier_status(available);
 619 }
 620
 621 void rcu_init(void)
 622 {
 623         if (init_done)
 624                 return;
 625         init_done = 1;
 626         rcu_sys_membarrier_init();
 627 }
 628 URCU_ATTR_ALIAS(urcu_stringify(rcu_init))
 629 void alias_rcu_init(void);
 630 #endif
 631
 632 #ifdef RCU_SIGNAL
 633 static void sigrcu_handler(int signo __attribute__((unused)),
 634                 siginfo_t *siginfo __attribute__((unused)),
 635                 void *context __attribute__((unused)))
 636 {
 637         /*
 638          * Executing this cmm_smp_mb() is the only purpose of this signal handler.
 639          * It punctually promotes cmm_barrier() into cmm_smp_mb() on every thread it is
 640          * executed on.
 641          */
 642         cmm_smp_mb();
 643         _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
 644         cmm_smp_mb();
 645 }
 646
 647 /*
 648  * rcu_init constructor. Called when the library is linked, but also when
 649  * reader threads are calling rcu_register_thread().
 650  * Should only be called by a single thread at a given time. This is ensured by
 651  * holing the rcu_registry_lock from rcu_register_thread() or by running
 652  * at library load time, which should not be executed by multiple
 653  * threads nor concurrently with rcu_register_thread() anyway.
 654  */
 655 void rcu_init(void)
 656 {
 657         struct sigaction act;
 658         int ret;
 659
 660         if (init_done)
 661                 return;
 662         init_done = 1;
 663
 664         act.sa_sigaction = sigrcu_handler;
 665         act.sa_flags = SA_SIGINFO | SA_RESTART;
 666         sigemptyset(&act.sa_mask);
 667         ret = sigaction(SIGRCU, &act, NULL);
 668         if (ret)
 669                 urcu_die(errno);
 670 }
 671 URCU_ATTR_ALIAS(urcu_stringify(rcu_init))
 672 void alias_rcu_init(void);
 673
 674 void rcu_exit(void)
 675 {
 676         /*
 677          * Don't unregister the SIGRCU signal handler anymore, because
 678          * call_rcu threads could still be using it shortly before the
 679          * application exits.
 680          * Assertion disabled because call_rcu threads are now rcu
 681          * readers, and left running at exit.
 682          * assert(cds_list_empty(&registry));
 683          */
 684 }
 685 URCU_ATTR_ALIAS(urcu_stringify(rcu_exit))
 686 void alias_rcu_exit(void);
 687
 688 #endif /* #ifdef RCU_SIGNAL */
 689
 690 DEFINE_RCU_FLAVOR(rcu_flavor);
 691 DEFINE_RCU_FLAVOR_ALIAS(rcu_flavor, alias_rcu_flavor);
 692
 693 #include "urcu-call-rcu-impl.h"
 694 #include "urcu-defer-impl.h"