urcu-bp.c

   1 /*
   2  * urcu-bp.c
   3  *
   4  * Userspace RCU library, "bulletproof" version.
   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 _GNU_SOURCE
  27 #define _LGPL_SOURCE
  28 #include <stdio.h>
  29 #include <pthread.h>
  30 #include <signal.h>
  31 #include <assert.h>
  32 #include <stdlib.h>
  33 #include <string.h>
  34 #include <errno.h>
  35 #include <poll.h>
  36 #include <unistd.h>
  37 #include <sys/mman.h>
  38
  39 #include "urcu/wfcqueue.h"
  40 #include "urcu/map/urcu-bp.h"
  41 #include "urcu/static/urcu-bp.h"
  42 #include "urcu-pointer.h"
  43 #include "urcu/tls-compat.h"
  44
  45 #include "urcu-die.h"
  46
  47 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
  48 #undef _LGPL_SOURCE
  49 #include "urcu-bp.h"
  50 #define _LGPL_SOURCE
  51
  52 #ifndef MAP_ANONYMOUS
  53 #define MAP_ANONYMOUS MAP_ANON
  54 #endif
  55
  56 #ifdef __linux__
  57 static
  58 void *mremap_wrapper(void *old_address, size_t old_size,
  59                 size_t new_size, int flags)
  60 {
  61         return mremap(old_address, old_size, new_size, flags);
  62 }
  63 #else
  64
  65 #define MREMAP_MAYMOVE  1
  66 #define MREMAP_FIXED    2
  67
  68 /*
  69  * mremap wrapper for non-Linux systems. Maps a RW, anonymous private mapping.
  70  * This is not generic.
  71 */
  72 static
  73 void *mremap_wrapper(void *old_address, size_t old_size,
  74                 size_t new_size, int flags)
  75 {
  76         void *new_address;
  77
  78         assert(flags & MREMAP_MAYMOVE);
  79         assert(!(flags & MREMAP_FIXED));
  80         new_address = mmap(old_address, new_size,
  81                            PROT_READ | PROT_WRITE,
  82                            MAP_ANONYMOUS | MAP_PRIVATE,
  83                            -1, 0);
  84         if (new_address == MAP_FAILED)
  85                 return MAP_FAILED;
  86         if (old_address) {
  87                 memcpy(new_address, old_address, old_size);
  88                 munmap(old_address, old_size);
  89         }
  90         return new_address;
  91 }
  92 #endif
  93
  94 /* Sleep delay in us */
  95 #define RCU_SLEEP_DELAY         1000
  96 #define ARENA_INIT_ALLOC        16
  97
  98 /*
  99  * Active attempts to check for reader Q.S. before calling sleep().
 100  */
 101 #define RCU_QS_ACTIVE_ATTEMPTS 100
 102
 103 void __attribute__((destructor)) rcu_bp_exit(void);
 104
 105 static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
 106
 107 #ifdef DEBUG_YIELD
 108 unsigned int rcu_yield_active;
 109 DEFINE_URCU_TLS(unsigned int, rcu_rand_yield);
 110 #endif
 111
 112 struct rcu_gp rcu_gp = { .ctr = RCU_GP_COUNT };
 113
 114 /*
 115  * Pointer to registry elements. Written to only by each individual reader. Read
 116  * by both the reader and the writers.
 117  */
 118 DEFINE_URCU_TLS(struct rcu_reader *, rcu_reader);
 119
 120 static CDS_LIST_HEAD(registry);
 121
 122 struct registry_arena {
 123         void *p;
 124         size_t len;
 125         size_t used;
 126 };
 127
 128 static struct registry_arena registry_arena;
 129
 130 /* Saved fork signal mask, protected by rcu_gp_lock */
 131 static sigset_t saved_fork_signal_mask;
 132
 133 static void rcu_gc_registry(void);
 134
 135 static void mutex_lock(pthread_mutex_t *mutex)
 136 {
 137         int ret;
 138
 139 #ifndef DISTRUST_SIGNALS_EXTREME
 140         ret = pthread_mutex_lock(mutex);
 141         if (ret)
 142                 urcu_die(ret);
 143 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
 144         while ((ret = pthread_mutex_trylock(mutex)) != 0) {
 145                 if (ret != EBUSY && ret != EINTR)
 146                         urcu_die(ret);
 147                 poll(NULL,0,10);
 148         }
 149 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
 150 }
 151
 152 static void mutex_unlock(pthread_mutex_t *mutex)
 153 {
 154         int ret;
 155
 156         ret = pthread_mutex_unlock(mutex);
 157         if (ret)
 158                 urcu_die(ret);
 159 }
 160
 161 static void wait_for_readers(struct cds_list_head *input_readers,
 162                         struct cds_list_head *cur_snap_readers,
 163                         struct cds_list_head *qsreaders)
 164 {
 165         int wait_loops = 0;
 166         struct rcu_reader *index, *tmp;
 167
 168         /*
 169          * Wait for each thread URCU_TLS(rcu_reader).ctr to either
 170          * indicate quiescence (not nested), or observe the current
 171          * rcu_gp.ctr value.
 172          */
 173         for (;;) {
 174                 wait_loops++;
 175                 cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
 176                         switch (rcu_reader_state(&index->ctr)) {
 177                         case RCU_READER_ACTIVE_CURRENT:
 178                                 if (cur_snap_readers) {
 179                                         cds_list_move(&index->node,
 180                                                 cur_snap_readers);
 181                                         break;
 182                                 }
 183                                 /* Fall-through */
 184                         case RCU_READER_INACTIVE:
 185                                 cds_list_move(&index->node, qsreaders);
 186                                 break;
 187                         case RCU_READER_ACTIVE_OLD:
 188                                 /*
 189                                  * Old snapshot. Leaving node in
 190                                  * input_readers will make us busy-loop
 191                                  * until the snapshot becomes current or
 192                                  * the reader becomes inactive.
 193                                  */
 194                                 break;
 195                         }
 196                 }
 197
 198                 if (cds_list_empty(input_readers)) {
 199                         break;
 200                 } else {
 201                         if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
 202                                 usleep(RCU_SLEEP_DELAY);
 203                         else
 204                                 caa_cpu_relax();
 205                 }
 206         }
 207 }
 208
 209 void synchronize_rcu(void)
 210 {
 211         CDS_LIST_HEAD(cur_snap_readers);
 212         CDS_LIST_HEAD(qsreaders);
 213         sigset_t newmask, oldmask;
 214         int ret;
 215
 216         ret = sigemptyset(&newmask);
 217         assert(!ret);
 218         ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
 219         assert(!ret);
 220
 221         mutex_lock(&rcu_gp_lock);
 222
 223         if (cds_list_empty(&registry))
 224                 goto out;
 225
 226         /* All threads should read qparity before accessing data structure
 227          * where new ptr points to. */
 228         /* Write new ptr before changing the qparity */
 229         cmm_smp_mb();
 230
 231         /* Remove old registry elements */
 232         rcu_gc_registry();
 233
 234         /*
 235          * Wait for readers to observe original parity or be quiescent.
 236          */
 237         wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
 238
 239         /*
 240          * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
 241          * model easier to understand. It does not have a big performance impact
 242          * anyway, given this is the write-side.
 243          */
 244         cmm_smp_mb();
 245
 246         /* Switch parity: 0 -> 1, 1 -> 0 */
 247         CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR_PHASE);
 248
 249         /*
 250          * Must commit qparity update to memory before waiting for other parity
 251          * quiescent state. Failure to do so could result in the writer waiting
 252          * forever while new readers are always accessing data (no progress).
 253          * Ensured by CMM_STORE_SHARED and CMM_LOAD_SHARED.
 254          */
 255
 256         /*
 257          * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
 258          * model easier to understand. It does not have a big performance impact
 259          * anyway, given this is the write-side.
 260          */
 261         cmm_smp_mb();
 262
 263         /*
 264          * Wait for readers to observe new parity or be quiescent.
 265          */
 266         wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
 267
 268         /*
 269          * Put quiescent reader list back into registry.
 270          */
 271         cds_list_splice(&qsreaders, &registry);
 272
 273         /*
 274          * Finish waiting for reader threads before letting the old ptr being
 275          * freed.
 276          */
 277         cmm_smp_mb();
 278 out:
 279         mutex_unlock(&rcu_gp_lock);
 280         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 281         assert(!ret);
 282 }
 283
 284 /*
 285  * library wrappers to be used by non-LGPL compatible source code.
 286  */
 287
 288 void rcu_read_lock(void)
 289 {
 290         _rcu_read_lock();
 291 }
 292
 293 void rcu_read_unlock(void)
 294 {
 295         _rcu_read_unlock();
 296 }
 297
 298 int rcu_read_ongoing(void)
 299 {
 300         return _rcu_read_ongoing();
 301 }
 302
 303 /*
 304  * only grow for now.
 305  */
 306 static void resize_arena(struct registry_arena *arena, size_t len)
 307 {
 308         void *new_arena;
 309
 310         if (!arena->p)
 311                 new_arena = mmap(arena->p, len,
 312                                  PROT_READ | PROT_WRITE,
 313                                  MAP_ANONYMOUS | MAP_PRIVATE,
 314                                  -1, 0);
 315         else
 316                 new_arena = mremap_wrapper(arena->p, arena->len,
 317                                         len, MREMAP_MAYMOVE);
 318         assert(new_arena != MAP_FAILED);
 319
 320         /*
 321          * re-used the same region ?
 322          */
 323         if (new_arena == arena->p)
 324                 return;
 325
 326         bzero(new_arena + arena->len, len - arena->len);
 327         arena->p = new_arena;
 328 }
 329
 330 /* Called with signals off and mutex locked */
 331 static void add_thread(void)
 332 {
 333         struct rcu_reader *rcu_reader_reg;
 334
 335         if (registry_arena.len
 336             < registry_arena.used + sizeof(struct rcu_reader))
 337                 resize_arena(&registry_arena,
 338                 caa_max(registry_arena.len << 1, ARENA_INIT_ALLOC));
 339         /*
 340          * Find a free spot.
 341          */
 342         for (rcu_reader_reg = registry_arena.p;
 343              (void *)rcu_reader_reg < registry_arena.p + registry_arena.len;
 344              rcu_reader_reg++) {
 345                 if (!rcu_reader_reg->alloc)
 346                         break;
 347         }
 348         rcu_reader_reg->alloc = 1;
 349         registry_arena.used += sizeof(struct rcu_reader);
 350
 351         /* Add to registry */
 352         rcu_reader_reg->tid = pthread_self();
 353         assert(rcu_reader_reg->ctr == 0);
 354         cds_list_add(&rcu_reader_reg->node, &registry);
 355         URCU_TLS(rcu_reader) = rcu_reader_reg;
 356 }
 357
 358 /* Called with signals off and mutex locked */
 359 static void rcu_gc_registry(void)
 360 {
 361         struct rcu_reader *rcu_reader_reg;
 362         pthread_t tid;
 363         int ret;
 364
 365         for (rcu_reader_reg = registry_arena.p;
 366              (void *)rcu_reader_reg < registry_arena.p + registry_arena.len;
 367              rcu_reader_reg++) {
 368                 if (!rcu_reader_reg->alloc)
 369                         continue;
 370                 tid = rcu_reader_reg->tid;
 371                 ret = pthread_kill(tid, 0);
 372                 assert(ret != EINVAL);
 373                 if (ret == ESRCH) {
 374                         cds_list_del(&rcu_reader_reg->node);
 375                         rcu_reader_reg->ctr = 0;
 376                         rcu_reader_reg->alloc = 0;
 377                         registry_arena.used -= sizeof(struct rcu_reader);
 378                 }
 379         }
 380 }
 381
 382 /* Disable signals, take mutex, add to registry */
 383 void rcu_bp_register(void)
 384 {
 385         sigset_t newmask, oldmask;
 386         int ret;
 387
 388         ret = sigemptyset(&newmask);
 389         assert(!ret);
 390         ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
 391         assert(!ret);
 392
 393         /*
 394          * Check if a signal concurrently registered our thread since
 395          * the check in rcu_read_lock(). */
 396         if (URCU_TLS(rcu_reader))
 397                 goto end;
 398
 399         mutex_lock(&rcu_gp_lock);
 400         add_thread();
 401         mutex_unlock(&rcu_gp_lock);
 402 end:
 403         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 404         assert(!ret);
 405 }
 406
 407 void rcu_bp_exit(void)
 408 {
 409         if (registry_arena.p)
 410                 munmap(registry_arena.p, registry_arena.len);
 411 }
 412
 413 /*
 414  * Holding the rcu_gp_lock across fork will make sure we fork() don't race with
 415  * a concurrent thread executing with this same lock held. This ensures that the
 416  * registry is in a coherent state in the child.
 417  */
 418 void rcu_bp_before_fork(void)
 419 {
 420         sigset_t newmask, oldmask;
 421         int ret;
 422
 423         ret = sigemptyset(&newmask);
 424         assert(!ret);
 425         ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
 426         assert(!ret);
 427         mutex_lock(&rcu_gp_lock);
 428         saved_fork_signal_mask = oldmask;
 429 }
 430
 431 void rcu_bp_after_fork_parent(void)
 432 {
 433         sigset_t oldmask;
 434         int ret;
 435
 436         oldmask = saved_fork_signal_mask;
 437         mutex_unlock(&rcu_gp_lock);
 438         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 439         assert(!ret);
 440 }
 441
 442 void rcu_bp_after_fork_child(void)
 443 {
 444         sigset_t oldmask;
 445         int ret;
 446
 447         rcu_gc_registry();
 448         oldmask = saved_fork_signal_mask;
 449         mutex_unlock(&rcu_gp_lock);
 450         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 451         assert(!ret);
 452 }
 453
 454 void *rcu_dereference_sym_bp(void *p)
 455 {
 456         return _rcu_dereference(p);
 457 }
 458
 459 void *rcu_set_pointer_sym_bp(void **p, void *v)
 460 {
 461         cmm_wmb();
 462         uatomic_set(p, v);
 463         return v;
 464 }
 465
 466 void *rcu_xchg_pointer_sym_bp(void **p, void *v)
 467 {
 468         cmm_wmb();
 469         return uatomic_xchg(p, v);
 470 }
 471
 472 void *rcu_cmpxchg_pointer_sym_bp(void **p, void *old, void *_new)
 473 {
 474         cmm_wmb();
 475         return uatomic_cmpxchg(p, old, _new);
 476 }
 477
 478 DEFINE_RCU_FLAVOR(rcu_flavor);
 479
 480 #include "urcu-call-rcu-impl.h"
 481 #include "urcu-defer-impl.h"