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 /*
 113  * Global grace period counter.
 114  * Contains the current RCU_GP_CTR_PHASE.
 115  * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
 116  * Written to only by writer with mutex taken. Read by both writer and readers.
 117  */
 118 unsigned long rcu_gp_ctr = RCU_GP_COUNT;
 119
 120 /*
 121  * Pointer to registry elements. Written to only by each individual reader. Read
 122  * by both the reader and the writers.
 123  */
 124 DEFINE_URCU_TLS(struct rcu_reader *, rcu_reader);
 125
 126 static CDS_LIST_HEAD(registry);
 127
 128 struct registry_arena {
 129         void *p;
 130         size_t len;
 131         size_t used;
 132 };
 133
 134 static struct registry_arena registry_arena;
 135
 136 /* Saved fork signal mask, protected by rcu_gp_lock */
 137 static sigset_t saved_fork_signal_mask;
 138
 139 static void rcu_gc_registry(void);
 140
 141 static void mutex_lock(pthread_mutex_t *mutex)
 142 {
 143         int ret;
 144
 145 #ifndef DISTRUST_SIGNALS_EXTREME
 146         ret = pthread_mutex_lock(mutex);
 147         if (ret)
 148                 urcu_die(ret);
 149 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
 150         while ((ret = pthread_mutex_trylock(mutex)) != 0) {
 151                 if (ret != EBUSY && ret != EINTR)
 152                         urcu_die(ret);
 153                 poll(NULL,0,10);
 154         }
 155 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
 156 }
 157
 158 static void mutex_unlock(pthread_mutex_t *mutex)
 159 {
 160         int ret;
 161
 162         ret = pthread_mutex_unlock(mutex);
 163         if (ret)
 164                 urcu_die(ret);
 165 }
 166
 167 static void wait_for_readers(struct cds_list_head *input_readers,
 168                         struct cds_list_head *cur_snap_readers,
 169                         struct cds_list_head *qsreaders)
 170 {
 171         int wait_loops = 0;
 172         struct rcu_reader *index, *tmp;
 173
 174         /*
 175          * Wait for each thread URCU_TLS(rcu_reader).ctr to either
 176          * indicate quiescence (not nested), or observe the current
 177          * rcu_gp_ctr value.
 178          */
 179         for (;;) {
 180                 wait_loops++;
 181                 cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
 182                         switch (rcu_reader_state(&index->ctr)) {
 183                         case RCU_READER_ACTIVE_CURRENT:
 184                                 if (cur_snap_readers) {
 185                                         cds_list_move(&index->node,
 186                                                 cur_snap_readers);
 187                                         break;
 188                                 }
 189                                 /* Fall-through */
 190                         case RCU_READER_INACTIVE:
 191                                 cds_list_move(&index->node, qsreaders);
 192                                 break;
 193                         case RCU_READER_ACTIVE_OLD:
 194                                 /*
 195                                  * Old snapshot. Leaving node in
 196                                  * input_readers will make us busy-loop
 197                                  * until the snapshot becomes current or
 198                                  * the reader becomes inactive.
 199                                  */
 200                                 break;
 201                         }
 202                 }
 203
 204                 if (cds_list_empty(input_readers)) {
 205                         break;
 206                 } else {
 207                         if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
 208                                 usleep(RCU_SLEEP_DELAY);
 209                         else
 210                                 caa_cpu_relax();
 211                 }
 212         }
 213 }
 214
 215 void synchronize_rcu(void)
 216 {
 217         CDS_LIST_HEAD(cur_snap_readers);
 218         CDS_LIST_HEAD(qsreaders);
 219         sigset_t newmask, oldmask;
 220         int ret;
 221
 222         ret = sigemptyset(&newmask);
 223         assert(!ret);
 224         ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
 225         assert(!ret);
 226
 227         mutex_lock(&rcu_gp_lock);
 228
 229         if (cds_list_empty(&registry))
 230                 goto out;
 231
 232         /* All threads should read qparity before accessing data structure
 233          * where new ptr points to. */
 234         /* Write new ptr before changing the qparity */
 235         cmm_smp_mb();
 236
 237         /* Remove old registry elements */
 238         rcu_gc_registry();
 239
 240         /*
 241          * Wait for readers to observe original parity or be quiescent.
 242          */
 243         wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
 244
 245         /*
 246          * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
 247          * model easier to understand. It does not have a big performance impact
 248          * anyway, given this is the write-side.
 249          */
 250         cmm_smp_mb();
 251
 252         /* Switch parity: 0 -> 1, 1 -> 0 */
 253         CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
 254
 255         /*
 256          * Must commit qparity update to memory before waiting for other parity
 257          * quiescent state. Failure to do so could result in the writer waiting
 258          * forever while new readers are always accessing data (no progress).
 259          * Ensured by CMM_STORE_SHARED and CMM_LOAD_SHARED.
 260          */
 261
 262         /*
 263          * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
 264          * model easier to understand. It does not have a big performance impact
 265          * anyway, given this is the write-side.
 266          */
 267         cmm_smp_mb();
 268
 269         /*
 270          * Wait for readers to observe new parity or be quiescent.
 271          */
 272         wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
 273
 274         /*
 275          * Put quiescent reader list back into registry.
 276          */
 277         cds_list_splice(&qsreaders, &registry);
 278
 279         /*
 280          * Finish waiting for reader threads before letting the old ptr being
 281          * freed.
 282          */
 283         cmm_smp_mb();
 284 out:
 285         mutex_unlock(&rcu_gp_lock);
 286         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 287         assert(!ret);
 288 }
 289
 290 /*
 291  * library wrappers to be used by non-LGPL compatible source code.
 292  */
 293
 294 void rcu_read_lock(void)
 295 {
 296         _rcu_read_lock();
 297 }
 298
 299 void rcu_read_unlock(void)
 300 {
 301         _rcu_read_unlock();
 302 }
 303
 304 int rcu_read_ongoing(void)
 305 {
 306         return _rcu_read_ongoing();
 307 }
 308
 309 /*
 310  * only grow for now.
 311  */
 312 static void resize_arena(struct registry_arena *arena, size_t len)
 313 {
 314         void *new_arena;
 315
 316         if (!arena->p)
 317                 new_arena = mmap(arena->p, len,
 318                                  PROT_READ | PROT_WRITE,
 319                                  MAP_ANONYMOUS | MAP_PRIVATE,
 320                                  -1, 0);
 321         else
 322                 new_arena = mremap_wrapper(arena->p, arena->len,
 323                                         len, MREMAP_MAYMOVE);
 324         assert(new_arena != MAP_FAILED);
 325
 326         /*
 327          * re-used the same region ?
 328          */
 329         if (new_arena == arena->p)
 330                 return;
 331
 332         bzero(new_arena + arena->len, len - arena->len);
 333         arena->p = new_arena;
 334 }
 335
 336 /* Called with signals off and mutex locked */
 337 static void add_thread(void)
 338 {
 339         struct rcu_reader *rcu_reader_reg;
 340
 341         if (registry_arena.len
 342             < registry_arena.used + sizeof(struct rcu_reader))
 343                 resize_arena(&registry_arena,
 344                 caa_max(registry_arena.len << 1, ARENA_INIT_ALLOC));
 345         /*
 346          * Find a free spot.
 347          */
 348         for (rcu_reader_reg = registry_arena.p;
 349              (void *)rcu_reader_reg < registry_arena.p + registry_arena.len;
 350              rcu_reader_reg++) {
 351                 if (!rcu_reader_reg->alloc)
 352                         break;
 353         }
 354         rcu_reader_reg->alloc = 1;
 355         registry_arena.used += sizeof(struct rcu_reader);
 356
 357         /* Add to registry */
 358         rcu_reader_reg->tid = pthread_self();
 359         assert(rcu_reader_reg->ctr == 0);
 360         cds_list_add(&rcu_reader_reg->node, &registry);
 361         URCU_TLS(rcu_reader) = rcu_reader_reg;
 362 }
 363
 364 /* Called with signals off and mutex locked */
 365 static void rcu_gc_registry(void)
 366 {
 367         struct rcu_reader *rcu_reader_reg;
 368         pthread_t tid;
 369         int ret;
 370
 371         for (rcu_reader_reg = registry_arena.p;
 372              (void *)rcu_reader_reg < registry_arena.p + registry_arena.len;
 373              rcu_reader_reg++) {
 374                 if (!rcu_reader_reg->alloc)
 375                         continue;
 376                 tid = rcu_reader_reg->tid;
 377                 ret = pthread_kill(tid, 0);
 378                 assert(ret != EINVAL);
 379                 if (ret == ESRCH) {
 380                         cds_list_del(&rcu_reader_reg->node);
 381                         rcu_reader_reg->ctr = 0;
 382                         rcu_reader_reg->alloc = 0;
 383                         registry_arena.used -= sizeof(struct rcu_reader);
 384                 }
 385         }
 386 }
 387
 388 /* Disable signals, take mutex, add to registry */
 389 void rcu_bp_register(void)
 390 {
 391         sigset_t newmask, oldmask;
 392         int ret;
 393
 394         ret = sigemptyset(&newmask);
 395         assert(!ret);
 396         ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
 397         assert(!ret);
 398
 399         /*
 400          * Check if a signal concurrently registered our thread since
 401          * the check in rcu_read_lock(). */
 402         if (URCU_TLS(rcu_reader))
 403                 goto end;
 404
 405         mutex_lock(&rcu_gp_lock);
 406         add_thread();
 407         mutex_unlock(&rcu_gp_lock);
 408 end:
 409         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 410         assert(!ret);
 411 }
 412
 413 void rcu_bp_exit(void)
 414 {
 415         if (registry_arena.p)
 416                 munmap(registry_arena.p, registry_arena.len);
 417 }
 418
 419 /*
 420  * Holding the rcu_gp_lock across fork will make sure we fork() don't race with
 421  * a concurrent thread executing with this same lock held. This ensures that the
 422  * registry is in a coherent state in the child.
 423  */
 424 void rcu_bp_before_fork(void)
 425 {
 426         sigset_t newmask, oldmask;
 427         int ret;
 428
 429         ret = sigemptyset(&newmask);
 430         assert(!ret);
 431         ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
 432         assert(!ret);
 433         mutex_lock(&rcu_gp_lock);
 434         saved_fork_signal_mask = oldmask;
 435 }
 436
 437 void rcu_bp_after_fork_parent(void)
 438 {
 439         sigset_t oldmask;
 440         int ret;
 441
 442         oldmask = saved_fork_signal_mask;
 443         mutex_unlock(&rcu_gp_lock);
 444         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 445         assert(!ret);
 446 }
 447
 448 void rcu_bp_after_fork_child(void)
 449 {
 450         sigset_t oldmask;
 451         int ret;
 452
 453         rcu_gc_registry();
 454         oldmask = saved_fork_signal_mask;
 455         mutex_unlock(&rcu_gp_lock);
 456         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 457         assert(!ret);
 458 }
 459
 460 void *rcu_dereference_sym_bp(void *p)
 461 {
 462         return _rcu_dereference(p);
 463 }
 464
 465 void *rcu_set_pointer_sym_bp(void **p, void *v)
 466 {
 467         cmm_wmb();
 468         uatomic_set(p, v);
 469         return v;
 470 }
 471
 472 void *rcu_xchg_pointer_sym_bp(void **p, void *v)
 473 {
 474         cmm_wmb();
 475         return uatomic_xchg(p, v);
 476 }
 477
 478 void *rcu_cmpxchg_pointer_sym_bp(void **p, void *old, void *_new)
 479 {
 480         cmm_wmb();
 481         return uatomic_cmpxchg(p, old, _new);
 482 }
 483
 484 DEFINE_RCU_FLAVOR(rcu_flavor);
 485
 486 #include "urcu-call-rcu-impl.h"
 487 #include "urcu-defer-impl.h"