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 #include <stdio.h>
  28 #include <pthread.h>
  29 #include <signal.h>
  30 #include <assert.h>
  31 #include <stdlib.h>
  32 #include <string.h>
  33 #include <errno.h>
  34 #include <poll.h>
  35 #include <unistd.h>
  36 #include <sys/mman.h>
  37
  38 #include "urcu/map/urcu-bp.h"
  39
  40 #include "urcu/static/urcu-bp.h"
  41 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
  42 #include "urcu-bp.h"
  43
  44 #ifndef MAP_ANONYMOUS
  45 #define MAP_ANONYMOUS MAP_ANON
  46 #endif
  47
  48 /* Sleep delay in us */
  49 #define RCU_SLEEP_DELAY         1000
  50 #define ARENA_INIT_ALLOC        16
  51
  52 void __attribute__((destructor)) rcu_bp_exit(void);
  53
  54 static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
  55
  56 #ifdef DEBUG_YIELD
  57 unsigned int yield_active;
  58 unsigned int __thread rand_yield;
  59 #endif
  60
  61 /*
  62  * Global grace period counter.
  63  * Contains the current RCU_GP_CTR_PHASE.
  64  * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
  65  * Written to only by writer with mutex taken. Read by both writer and readers.
  66  */
  67 long rcu_gp_ctr = RCU_GP_COUNT;
  68
  69 /*
  70  * Pointer to registry elements. Written to only by each individual reader. Read
  71  * by both the reader and the writers.
  72  */
  73 struct rcu_reader __thread *rcu_reader;
  74
  75 static CDS_LIST_HEAD(registry);
  76
  77 struct registry_arena {
  78         void *p;
  79         size_t len;
  80         size_t used;
  81 };
  82
  83 static struct registry_arena registry_arena;
  84
  85 /* Saved fork signal mask, protected by rcu_gp_lock */
  86 static sigset_t saved_fork_signal_mask;
  87
  88 static void rcu_gc_registry(void);
  89
  90 static void mutex_lock(pthread_mutex_t *mutex)
  91 {
  92         int ret;
  93
  94 #ifndef DISTRUST_SIGNALS_EXTREME
  95         ret = pthread_mutex_lock(mutex);
  96         if (ret) {
  97                 perror("Error in pthread mutex lock");
  98                 exit(-1);
  99         }
 100 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
 101         while ((ret = pthread_mutex_trylock(mutex)) != 0) {
 102                 if (ret != EBUSY && ret != EINTR) {
 103                         printf("ret = %d, errno = %d\n", ret, errno);
 104                         perror("Error in pthread mutex lock");
 105                         exit(-1);
 106                 }
 107                 poll(NULL,0,10);
 108         }
 109 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
 110 }
 111
 112 static void mutex_unlock(pthread_mutex_t *mutex)
 113 {
 114         int ret;
 115
 116         ret = pthread_mutex_unlock(mutex);
 117         if (ret) {
 118                 perror("Error in pthread mutex unlock");
 119                 exit(-1);
 120         }
 121 }
 122
 123 void update_counter_and_wait(void)
 124 {
 125         CDS_LIST_HEAD(qsreaders);
 126         int wait_loops = 0;
 127         struct rcu_reader *index, *tmp;
 128
 129         /* Switch parity: 0 -> 1, 1 -> 0 */
 130         CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
 131
 132         /*
 133          * Must commit qparity update to memory before waiting for other parity
 134          * quiescent state. Failure to do so could result in the writer waiting
 135          * forever while new readers are always accessing data (no progress).
 136          * Ensured by CMM_STORE_SHARED and CMM_LOAD_SHARED.
 137          */
 138
 139         /*
 140          * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
 141          * model easier to understand. It does not have a big performance impact
 142          * anyway, given this is the write-side.
 143          */
 144         cmm_smp_mb();
 145
 146         /*
 147          * Wait for each thread rcu_reader.ctr count to become 0.
 148          */
 149         for (;;) {
 150                 wait_loops++;
 151                 cds_list_for_each_entry_safe(index, tmp, &registry, node) {
 152                         if (!rcu_old_gp_ongoing(&index->ctr))
 153                                 cds_list_move(&index->node, &qsreaders);
 154                 }
 155
 156                 if (cds_list_empty(&registry)) {
 157                         break;
 158                 } else {
 159                         if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
 160                                 usleep(RCU_SLEEP_DELAY);
 161                         else
 162                                 caa_cpu_relax();
 163                 }
 164         }
 165         /* put back the reader list in the registry */
 166         cds_list_splice(&qsreaders, &registry);
 167 }
 168
 169 void synchronize_rcu(void)
 170 {
 171         sigset_t newmask, oldmask;
 172         int ret;
 173
 174         ret = sigemptyset(&newmask);
 175         assert(!ret);
 176         ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
 177         assert(!ret);
 178
 179         mutex_lock(&rcu_gp_lock);
 180
 181         if (cds_list_empty(&registry))
 182                 goto out;
 183
 184         /* All threads should read qparity before accessing data structure
 185          * where new ptr points to. */
 186         /* Write new ptr before changing the qparity */
 187         cmm_smp_mb();
 188
 189         /* Remove old registry elements */
 190         rcu_gc_registry();
 191
 192         /*
 193          * Wait for previous parity to be empty of readers.
 194          */
 195         update_counter_and_wait();      /* 0 -> 1, wait readers in parity 0 */
 196
 197         /*
 198          * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
 199          * model easier to understand. It does not have a big performance impact
 200          * anyway, given this is the write-side.
 201          */
 202         cmm_smp_mb();
 203
 204         /*
 205          * Wait for previous parity to be empty of readers.
 206          */
 207         update_counter_and_wait();      /* 1 -> 0, wait readers in parity 1 */
 208
 209         /*
 210          * Finish waiting for reader threads before letting the old ptr being
 211          * freed.
 212          */
 213         cmm_smp_mb();
 214 out:
 215         mutex_unlock(&rcu_gp_lock);
 216         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 217         assert(!ret);
 218 }
 219
 220 /*
 221  * library wrappers to be used by non-LGPL compatible source code.
 222  */
 223
 224 void rcu_read_lock(void)
 225 {
 226         _rcu_read_lock();
 227 }
 228
 229 void rcu_read_unlock(void)
 230 {
 231         _rcu_read_unlock();
 232 }
 233
 234 /*
 235  * only grow for now.
 236  */
 237 static void resize_arena(struct registry_arena *arena, size_t len)
 238 {
 239         void *new_arena;
 240
 241         if (!arena->p)
 242                 new_arena = mmap(arena->p, len,
 243                                  PROT_READ | PROT_WRITE,
 244                                  MAP_ANONYMOUS | MAP_PRIVATE,
 245                                  -1, 0);
 246         else
 247                 new_arena = mremap(arena->p, arena->len,
 248                                    len, MREMAP_MAYMOVE);
 249         assert(new_arena != MAP_FAILED);
 250
 251         /*
 252          * re-used the same region ?
 253          */
 254         if (new_arena == arena->p)
 255                 return;
 256
 257         bzero(new_arena + arena->len, len - arena->len);
 258         arena->p = new_arena;
 259 }
 260
 261 /* Called with signals off and mutex locked */
 262 static void add_thread(void)
 263 {
 264         struct rcu_reader *rcu_reader_reg;
 265
 266         if (registry_arena.len
 267             < registry_arena.used + sizeof(struct rcu_reader))
 268                 resize_arena(&registry_arena,
 269                 max(registry_arena.len << 1, ARENA_INIT_ALLOC));
 270         /*
 271          * Find a free spot.
 272          */
 273         for (rcu_reader_reg = registry_arena.p;
 274              (void *)rcu_reader_reg < registry_arena.p + registry_arena.len;
 275              rcu_reader_reg++) {
 276                 if (!rcu_reader_reg->alloc)
 277                         break;
 278         }
 279         rcu_reader_reg->alloc = 1;
 280         registry_arena.used += sizeof(struct rcu_reader);
 281
 282         /* Add to registry */
 283         rcu_reader_reg->tid = pthread_self();
 284         assert(rcu_reader_reg->ctr == 0);
 285         cds_list_add(&rcu_reader_reg->node, &registry);
 286         rcu_reader = rcu_reader_reg;
 287 }
 288
 289 /* Called with signals off and mutex locked */
 290 static void rcu_gc_registry(void)
 291 {
 292         struct rcu_reader *rcu_reader_reg;
 293         pthread_t tid;
 294         int ret;
 295
 296         for (rcu_reader_reg = registry_arena.p;
 297              (void *)rcu_reader_reg < registry_arena.p + registry_arena.len;
 298              rcu_reader_reg++) {
 299                 if (!rcu_reader_reg->alloc)
 300                         continue;
 301                 tid = rcu_reader_reg->tid;
 302                 ret = pthread_kill(tid, 0);
 303                 assert(ret != EINVAL);
 304                 if (ret == ESRCH) {
 305                         cds_list_del(&rcu_reader_reg->node);
 306                         rcu_reader_reg->ctr = 0;
 307                         rcu_reader_reg->alloc = 0;
 308                         registry_arena.used -= sizeof(struct rcu_reader);
 309                 }
 310         }
 311 }
 312
 313 /* Disable signals, take mutex, add to registry */
 314 void rcu_bp_register(void)
 315 {
 316         sigset_t newmask, oldmask;
 317         int ret;
 318
 319         ret = sigemptyset(&newmask);
 320         assert(!ret);
 321         ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
 322         assert(!ret);
 323
 324         /*
 325          * Check if a signal concurrently registered our thread since
 326          * the check in rcu_read_lock(). */
 327         if (rcu_reader)
 328                 goto end;
 329
 330         mutex_lock(&rcu_gp_lock);
 331         add_thread();
 332         mutex_unlock(&rcu_gp_lock);
 333 end:
 334         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 335         assert(!ret);
 336 }
 337
 338 void rcu_bp_exit()
 339 {
 340         munmap(registry_arena.p, registry_arena.len);
 341 }
 342
 343 /*
 344  * Holding the rcu_gp_lock across fork will make sure we fork() don't race with
 345  * a concurrent thread executing with this same lock held. This ensures that the
 346  * registry is in a coherent state in the child.
 347  */
 348 void rcu_bp_before_fork(void)
 349 {
 350         sigset_t newmask, oldmask;
 351         int ret;
 352
 353         ret = sigemptyset(&newmask);
 354         assert(!ret);
 355         ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
 356         assert(!ret);
 357         mutex_lock(&rcu_gp_lock);
 358         saved_fork_signal_mask = oldmask;
 359 }
 360
 361 void rcu_bp_after_fork_parent(void)
 362 {
 363         sigset_t oldmask;
 364         int ret;
 365
 366         oldmask = saved_fork_signal_mask;
 367         mutex_unlock(&rcu_gp_lock);
 368         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 369         assert(!ret);
 370 }
 371
 372 void rcu_bp_after_fork_child(void)
 373 {
 374         sigset_t oldmask;
 375         int ret;
 376
 377         rcu_gc_registry();
 378         oldmask = saved_fork_signal_mask;
 379         mutex_unlock(&rcu_gp_lock);
 380         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 381         assert(!ret);
 382 }
 383
 384 #include "urcu-call-rcu-impl.h"
 385 #include "urcu-defer-impl.h"