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