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