src/urcu-call-rcu-impl.h

   1 /*
   2  * urcu-call-rcu.c
   3  *
   4  * Userspace RCU library - batch memory reclamation with kernel API
   5  *
   6  * Copyright (c) 2010 Paul E. McKenney <paulmck@linux.vnet.ibm.com>
   7  *
   8  * This library is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License as published by the Free Software Foundation; either
  11  * version 2.1 of the License, or (at your option) any later version.
  12  *
  13  * This library is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public
  19  * License along with this library; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  21  */
  22
  23 #define _LGPL_SOURCE
  24 #include <stdio.h>
  25 #include <pthread.h>
  26 #include <signal.h>
  27 #include <assert.h>
  28 #include <stdlib.h>
  29 #include <stdint.h>
  30 #include <string.h>
  31 #include <errno.h>
  32 #include <poll.h>
  33 #include <sys/time.h>
  34 #include <unistd.h>
  35 #include <sched.h>
  36
  37 #include "compat-getcpu.h"
  38 #include <urcu/wfcqueue.h>
  39 #include <urcu/call-rcu.h>
  40 #include <urcu/pointer.h>
  41 #include <urcu/list.h>
  42 #include <urcu/futex.h>
  43 #include <urcu/tls-compat.h>
  44 #include <urcu/ref.h>
  45 #include "urcu-die.h"
  46 #include "urcu-utils.h"
  47 #include "compat-smp.h"
  48
  49 #define SET_AFFINITY_CHECK_PERIOD               (1U << 8)       /* 256 */
  50 #define SET_AFFINITY_CHECK_PERIOD_MASK          (SET_AFFINITY_CHECK_PERIOD - 1)
  51
  52 /* Data structure that identifies a call_rcu thread. */
  53
  54 struct call_rcu_data {
  55         /*
  56          * We do not align head on a different cache-line than tail
  57          * mainly because call_rcu callback-invocation threads use
  58          * batching ("splice") to get an entire list of callbacks, which
  59          * effectively empties the queue, and requires to touch the tail
  60          * anyway.
  61          */
  62         struct cds_wfcq_tail cbs_tail;
  63         struct cds_wfcq_head cbs_head;
  64         unsigned long flags;
  65         int32_t futex;
  66         unsigned long qlen; /* maintained for debugging. */
  67         pthread_t tid;
  68         int cpu_affinity;
  69         unsigned long gp_count;
  70         struct cds_list_head list;
  71 } __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
  72
  73 struct call_rcu_completion {
  74         int barrier_count;
  75         int32_t futex;
  76         struct urcu_ref ref;
  77 };
  78
  79 struct call_rcu_completion_work {
  80         struct rcu_head head;
  81         struct call_rcu_completion *completion;
  82 };
  83
  84 enum crdf_flags {
  85         CRDF_FLAG_JOIN_THREAD = (1 << 0),
  86 };
  87
  88 /*
  89  * List of all call_rcu_data structures to keep valgrind happy.
  90  * Protected by call_rcu_mutex.
  91  */
  92
  93 static CDS_LIST_HEAD(call_rcu_data_list);
  94
  95 /* Link a thread using call_rcu() to its call_rcu thread. */
  96
  97 static DEFINE_URCU_TLS(struct call_rcu_data *, thread_call_rcu_data);
  98
  99 /*
 100  * Guard call_rcu thread creation and atfork handlers.
 101  */
 102 static pthread_mutex_t call_rcu_mutex = PTHREAD_MUTEX_INITIALIZER;
 103
 104 /* If a given thread does not have its own call_rcu thread, this is default. */
 105
 106 static struct call_rcu_data *default_call_rcu_data;
 107
 108 static struct urcu_atfork *registered_rculfhash_atfork;
 109
 110 /*
 111  * If the sched_getcpu() and sysconf(_SC_NPROCESSORS_CONF) calls are
 112  * available, then we can have call_rcu threads assigned to individual
 113  * CPUs rather than only to specific threads.
 114  */
 115
 116 #if defined(HAVE_SYSCONF) && (defined(HAVE_SCHED_GETCPU) || defined(HAVE_GETCPUID))
 117
 118 /*
 119  * Pointer to array of pointers to per-CPU call_rcu_data structures
 120  * and # CPUs. per_cpu_call_rcu_data is a RCU-protected pointer to an
 121  * array of RCU-protected pointers to call_rcu_data. call_rcu acts as a
 122  * RCU read-side and reads per_cpu_call_rcu_data and the per-cpu pointer
 123  * without mutex. The call_rcu_mutex protects updates.
 124  */
 125
 126 static struct call_rcu_data **per_cpu_call_rcu_data;
 127 static long cpus_array_len;
 128
 129 static void cpus_array_len_reset(void)
 130 {
 131         cpus_array_len = 0;
 132 }
 133
 134 /* Allocate the array if it has not already been allocated. */
 135
 136 static void alloc_cpu_call_rcu_data(void)
 137 {
 138         struct call_rcu_data **p;
 139         static int warned = 0;
 140
 141         if (cpus_array_len != 0)
 142                 return;
 143         cpus_array_len = get_possible_cpus_array_len();
 144         if (cpus_array_len <= 0) {
 145                 return;
 146         }
 147         p = malloc(cpus_array_len * sizeof(*per_cpu_call_rcu_data));
 148         if (p != NULL) {
 149                 memset(p, '\0', cpus_array_len * sizeof(*per_cpu_call_rcu_data));
 150                 rcu_set_pointer(&per_cpu_call_rcu_data, p);
 151         } else {
 152                 if (!warned) {
 153                         fprintf(stderr, "[error] liburcu: unable to allocate per-CPU pointer array\n");
 154                 }
 155                 warned = 1;
 156         }
 157 }
 158
 159 #else /* #if defined(HAVE_SYSCONF) && defined(HAVE_SCHED_GETCPU) */
 160
 161 /*
 162  * per_cpu_call_rcu_data should be constant, but some functions below, used both
 163  * for cases where cpu number is available and not available, assume it it not
 164  * constant.
 165  */
 166 static struct call_rcu_data **per_cpu_call_rcu_data = NULL;
 167 static const long cpus_array_len = -1;
 168
 169 static void cpus_array_len_reset(void)
 170 {
 171 }
 172
 173 static void alloc_cpu_call_rcu_data(void)
 174 {
 175 }
 176
 177 #endif /* #else #if defined(HAVE_SYSCONF) && defined(HAVE_SCHED_GETCPU) */
 178
 179 /* Acquire the specified pthread mutex. */
 180
 181 static void call_rcu_lock(pthread_mutex_t *pmp)
 182 {
 183         int ret;
 184
 185         ret = pthread_mutex_lock(pmp);
 186         if (ret)
 187                 urcu_die(ret);
 188 }
 189
 190 /* Release the specified pthread mutex. */
 191
 192 static void call_rcu_unlock(pthread_mutex_t *pmp)
 193 {
 194         int ret;
 195
 196         ret = pthread_mutex_unlock(pmp);
 197         if (ret)
 198                 urcu_die(ret);
 199 }
 200
 201 /*
 202  * Periodically retry setting CPU affinity if we migrate.
 203  * Losing affinity can be caused by CPU hotunplug/hotplug, or by
 204  * cpuset(7).
 205  */
 206 #ifdef HAVE_SCHED_SETAFFINITY
 207 static
 208 int set_thread_cpu_affinity(struct call_rcu_data *crdp)
 209 {
 210         cpu_set_t mask;
 211         int ret;
 212
 213         if (crdp->cpu_affinity < 0)
 214                 return 0;
 215         if (++crdp->gp_count & SET_AFFINITY_CHECK_PERIOD_MASK)
 216                 return 0;
 217         if (urcu_sched_getcpu() == crdp->cpu_affinity)
 218                 return 0;
 219
 220         CPU_ZERO(&mask);
 221         CPU_SET(crdp->cpu_affinity, &mask);
 222 #if SCHED_SETAFFINITY_ARGS == 2
 223         ret = sched_setaffinity(0, &mask);
 224 #else
 225         ret = sched_setaffinity(0, sizeof(mask), &mask);
 226 #endif
 227         /*
 228          * EINVAL is fine: can be caused by hotunplugged CPUs, or by
 229          * cpuset(7). This is why we should always retry if we detect
 230          * migration.
 231          */
 232         if (ret && errno == EINVAL) {
 233                 ret = 0;
 234                 errno = 0;
 235         }
 236         return ret;
 237 }
 238 #else
 239 static
 240 int set_thread_cpu_affinity(struct call_rcu_data *crdp __attribute__((unused)))
 241 {
 242         return 0;
 243 }
 244 #endif
 245
 246 static void call_rcu_wait(struct call_rcu_data *crdp)
 247 {
 248         /* Read call_rcu list before read futex */
 249         cmm_smp_mb();
 250         while (uatomic_read(&crdp->futex) == -1) {
 251                 if (!futex_async(&crdp->futex, FUTEX_WAIT, -1, NULL, NULL, 0)) {
 252                         /*
 253                          * Prior queued wakeups queued by unrelated code
 254                          * using the same address can cause futex wait to
 255                          * return 0 even through the futex value is still
 256                          * -1 (spurious wakeups). Check the value again
 257                          * in user-space to validate whether it really
 258                          * differs from -1.
 259                          */
 260                         continue;
 261                 }
 262                 switch (errno) {
 263                 case EAGAIN:
 264                         /* Value already changed. */
 265                         return;
 266                 case EINTR:
 267                         /* Retry if interrupted by signal. */
 268                         break;  /* Get out of switch. Check again. */
 269                 default:
 270                         /* Unexpected error. */
 271                         urcu_die(errno);
 272                 }
 273         }
 274 }
 275
 276 static void call_rcu_wake_up(struct call_rcu_data *crdp)
 277 {
 278         /* Write to call_rcu list before reading/writing futex */
 279         cmm_smp_mb();
 280         if (caa_unlikely(uatomic_read(&crdp->futex) == -1)) {
 281                 uatomic_set(&crdp->futex, 0);
 282                 if (futex_async(&crdp->futex, FUTEX_WAKE, 1,
 283                                 NULL, NULL, 0) < 0)
 284                         urcu_die(errno);
 285         }
 286 }
 287
 288 static void call_rcu_completion_wait(struct call_rcu_completion *completion)
 289 {
 290         /* Read completion barrier count before read futex */
 291         cmm_smp_mb();
 292         while (uatomic_read(&completion->futex) == -1) {
 293                 if (!futex_async(&completion->futex, FUTEX_WAIT, -1, NULL, NULL, 0)) {
 294                         /*
 295                          * Prior queued wakeups queued by unrelated code
 296                          * using the same address can cause futex wait to
 297                          * return 0 even through the futex value is still
 298                          * -1 (spurious wakeups). Check the value again
 299                          * in user-space to validate whether it really
 300                          * differs from -1.
 301                          */
 302                         continue;
 303                 }
 304                 switch (errno) {
 305                 case EAGAIN:
 306                         /* Value already changed. */
 307                         return;
 308                 case EINTR:
 309                         /* Retry if interrupted by signal. */
 310                         break;  /* Get out of switch. Check again. */
 311                 default:
 312                         /* Unexpected error. */
 313                         urcu_die(errno);
 314                 }
 315         }
 316 }
 317
 318 static void call_rcu_completion_wake_up(struct call_rcu_completion *completion)
 319 {
 320         /* Write to completion barrier count before reading/writing futex */
 321         cmm_smp_mb();
 322         if (caa_unlikely(uatomic_read(&completion->futex) == -1)) {
 323                 uatomic_set(&completion->futex, 0);
 324                 if (futex_async(&completion->futex, FUTEX_WAKE, 1,
 325                                 NULL, NULL, 0) < 0)
 326                         urcu_die(errno);
 327         }
 328 }
 329
 330 /* This is the code run by each call_rcu thread. */
 331
 332 static void *call_rcu_thread(void *arg)
 333 {
 334         unsigned long cbcount;
 335         struct call_rcu_data *crdp = (struct call_rcu_data *) arg;
 336         int rt = !!(uatomic_read(&crdp->flags) & URCU_CALL_RCU_RT);
 337
 338         if (set_thread_cpu_affinity(crdp))
 339                 urcu_die(errno);
 340
 341         /*
 342          * If callbacks take a read-side lock, we need to be registered.
 343          */
 344         rcu_register_thread();
 345
 346         URCU_TLS(thread_call_rcu_data) = crdp;
 347         if (!rt) {
 348                 uatomic_dec(&crdp->futex);
 349                 /* Decrement futex before reading call_rcu list */
 350                 cmm_smp_mb();
 351         }
 352         for (;;) {
 353                 struct cds_wfcq_head cbs_tmp_head;
 354                 struct cds_wfcq_tail cbs_tmp_tail;
 355                 struct cds_wfcq_node *cbs, *cbs_tmp_n;
 356                 enum cds_wfcq_ret splice_ret;
 357
 358                 if (set_thread_cpu_affinity(crdp))
 359                         urcu_die(errno);
 360
 361                 if (uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSE) {
 362                         /*
 363                          * Pause requested. Become quiescent: remove
 364                          * ourself from all global lists, and don't
 365                          * process any callback. The callback lists may
 366                          * still be non-empty though.
 367                          */
 368                         rcu_unregister_thread();
 369                         cmm_smp_mb__before_uatomic_or();
 370                         uatomic_or(&crdp->flags, URCU_CALL_RCU_PAUSED);
 371                         while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSE) != 0)
 372                                 (void) poll(NULL, 0, 1);
 373                         uatomic_and(&crdp->flags, ~URCU_CALL_RCU_PAUSED);
 374                         cmm_smp_mb__after_uatomic_and();
 375                         rcu_register_thread();
 376                 }
 377
 378                 cds_wfcq_init(&cbs_tmp_head, &cbs_tmp_tail);
 379                 splice_ret = __cds_wfcq_splice_blocking(&cbs_tmp_head,
 380                         &cbs_tmp_tail, &crdp->cbs_head, &crdp->cbs_tail);
 381                 assert(splice_ret != CDS_WFCQ_RET_WOULDBLOCK);
 382                 assert(splice_ret != CDS_WFCQ_RET_DEST_NON_EMPTY);
 383                 if (splice_ret != CDS_WFCQ_RET_SRC_EMPTY) {
 384                         synchronize_rcu();
 385                         cbcount = 0;
 386                         __cds_wfcq_for_each_blocking_safe(&cbs_tmp_head,
 387                                         &cbs_tmp_tail, cbs, cbs_tmp_n) {
 388                                 struct rcu_head *rhp;
 389
 390                                 rhp = caa_container_of(cbs,
 391                                         struct rcu_head, next);
 392                                 rhp->func(rhp);
 393                                 cbcount++;
 394                         }
 395                         uatomic_sub(&crdp->qlen, cbcount);
 396                 }
 397                 if (uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOP)
 398                         break;
 399                 rcu_thread_offline();
 400                 if (!rt) {
 401                         if (cds_wfcq_empty(&crdp->cbs_head,
 402                                         &crdp->cbs_tail)) {
 403                                 call_rcu_wait(crdp);
 404                                 (void) poll(NULL, 0, 10);
 405                                 uatomic_dec(&crdp->futex);
 406                                 /*
 407                                  * Decrement futex before reading
 408                                  * call_rcu list.
 409                                  */
 410                                 cmm_smp_mb();
 411                         } else {
 412                                 (void) poll(NULL, 0, 10);
 413                         }
 414                 } else {
 415                         (void) poll(NULL, 0, 10);
 416                 }
 417                 rcu_thread_online();
 418         }
 419         if (!rt) {
 420                 /*
 421                  * Read call_rcu list before write futex.
 422                  */
 423                 cmm_smp_mb();
 424                 uatomic_set(&crdp->futex, 0);
 425         }
 426         uatomic_or(&crdp->flags, URCU_CALL_RCU_STOPPED);
 427         rcu_unregister_thread();
 428         return NULL;
 429 }
 430
 431 /*
 432  * Create both a call_rcu thread and the corresponding call_rcu_data
 433  * structure, linking the structure in as specified.  Caller must hold
 434  * call_rcu_mutex.
 435  */
 436
 437 static void call_rcu_data_init(struct call_rcu_data **crdpp,
 438                                unsigned long flags,
 439                                int cpu_affinity)
 440 {
 441         struct call_rcu_data *crdp;
 442         int ret;
 443
 444         crdp = malloc(sizeof(*crdp));
 445         if (crdp == NULL)
 446                 urcu_die(errno);
 447         memset(crdp, '\0', sizeof(*crdp));
 448         cds_wfcq_init(&crdp->cbs_head, &crdp->cbs_tail);
 449         crdp->qlen = 0;
 450         crdp->futex = 0;
 451         crdp->flags = flags;
 452         cds_list_add(&crdp->list, &call_rcu_data_list);
 453         crdp->cpu_affinity = cpu_affinity;
 454         crdp->gp_count = 0;
 455         rcu_set_pointer(crdpp, crdp);
 456
 457         ret = pthread_create(&crdp->tid, NULL, call_rcu_thread, crdp);
 458         if (ret)
 459                 urcu_die(ret);
 460 }
 461
 462 /*
 463  * Return a pointer to the call_rcu_data structure for the specified
 464  * CPU, returning NULL if there is none.  We cannot automatically
 465  * created it because the platform we are running on might not define
 466  * urcu_sched_getcpu().
 467  *
 468  * The call to this function and use of the returned call_rcu_data
 469  * should be protected by RCU read-side lock.
 470  */
 471
 472 struct call_rcu_data *get_cpu_call_rcu_data(int cpu)
 473 {
 474         static int warned = 0;
 475         struct call_rcu_data **pcpu_crdp;
 476
 477         pcpu_crdp = rcu_dereference(per_cpu_call_rcu_data);
 478         if (pcpu_crdp == NULL)
 479                 return NULL;
 480         if (!warned && cpus_array_len > 0 && (cpu < 0 || cpus_array_len <= cpu)) {
 481                 fprintf(stderr, "[error] liburcu: get CPU # out of range\n");
 482                 warned = 1;
 483         }
 484         if (cpu < 0 || cpus_array_len <= cpu)
 485                 return NULL;
 486         return rcu_dereference(pcpu_crdp[cpu]);
 487 }
 488 URCU_ATTR_ALIAS(urcu_stringify(get_cpu_call_rcu_data))
 489 struct call_rcu_data *alias_get_cpu_call_rcu_data();
 490
 491 /*
 492  * Return the tid corresponding to the call_rcu thread whose
 493  * call_rcu_data structure is specified.
 494  */
 495
 496 pthread_t get_call_rcu_thread(struct call_rcu_data *crdp)
 497 {
 498         return crdp->tid;
 499 }
 500 URCU_ATTR_ALIAS(urcu_stringify(get_call_rcu_thread))
 501 pthread_t alias_get_call_rcu_thread();
 502
 503 /*
 504  * Create a call_rcu_data structure (with thread) and return a pointer.
 505  */
 506
 507 static struct call_rcu_data *__create_call_rcu_data(unsigned long flags,
 508                                                     int cpu_affinity)
 509 {
 510         struct call_rcu_data *crdp;
 511
 512         call_rcu_data_init(&crdp, flags, cpu_affinity);
 513         return crdp;
 514 }
 515
 516 URCU_ATTR_ALIAS(urcu_stringify(create_call_rcu_data))
 517 struct call_rcu_data *alias_create_call_rcu_data();
 518 struct call_rcu_data *create_call_rcu_data(unsigned long flags,
 519                                            int cpu_affinity)
 520 {
 521         struct call_rcu_data *crdp;
 522
 523         call_rcu_lock(&call_rcu_mutex);
 524         crdp = __create_call_rcu_data(flags, cpu_affinity);
 525         call_rcu_unlock(&call_rcu_mutex);
 526         return crdp;
 527 }
 528
 529 /*
 530  * Set the specified CPU to use the specified call_rcu_data structure.
 531  *
 532  * Use NULL to remove a CPU's call_rcu_data structure, but it is
 533  * the caller's responsibility to dispose of the removed structure.
 534  * Use get_cpu_call_rcu_data() to obtain a pointer to the old structure
 535  * (prior to NULLing it out, of course).
 536  *
 537  * The caller must wait for a grace-period to pass between return from
 538  * set_cpu_call_rcu_data() and call to call_rcu_data_free() passing the
 539  * previous call rcu data as argument.
 540  */
 541
 542 int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp)
 543 {
 544         static int warned = 0;
 545
 546         call_rcu_lock(&call_rcu_mutex);
 547         alloc_cpu_call_rcu_data();
 548         if (cpu < 0 || cpus_array_len <= cpu) {
 549                 if (!warned) {
 550                         fprintf(stderr, "[error] liburcu: set CPU # out of range\n");
 551                         warned = 1;
 552                 }
 553                 call_rcu_unlock(&call_rcu_mutex);
 554                 errno = EINVAL;
 555                 return -EINVAL;
 556         }
 557
 558         if (per_cpu_call_rcu_data == NULL) {
 559                 call_rcu_unlock(&call_rcu_mutex);
 560                 errno = ENOMEM;
 561                 return -ENOMEM;
 562         }
 563
 564         if (per_cpu_call_rcu_data[cpu] != NULL && crdp != NULL) {
 565                 call_rcu_unlock(&call_rcu_mutex);
 566                 errno = EEXIST;
 567                 return -EEXIST;
 568         }
 569
 570         rcu_set_pointer(&per_cpu_call_rcu_data[cpu], crdp);
 571         call_rcu_unlock(&call_rcu_mutex);
 572         return 0;
 573 }
 574 URCU_ATTR_ALIAS(urcu_stringify(set_cpu_call_rcu_data))
 575 int alias_set_cpu_call_rcu_data();
 576
 577 /*
 578  * Return a pointer to the default call_rcu_data structure, creating
 579  * one if need be.
 580  *
 581  * The call to this function with intent to use the returned
 582  * call_rcu_data should be protected by RCU read-side lock.
 583  */
 584
 585 struct call_rcu_data *get_default_call_rcu_data(void)
 586 {
 587         struct call_rcu_data *crdp;
 588
 589         crdp = rcu_dereference(default_call_rcu_data);
 590         if (crdp != NULL)
 591                 return crdp;
 592
 593         call_rcu_lock(&call_rcu_mutex);
 594         if (default_call_rcu_data == NULL)
 595                 call_rcu_data_init(&default_call_rcu_data, 0, -1);
 596         crdp = default_call_rcu_data;
 597         call_rcu_unlock(&call_rcu_mutex);
 598
 599         return crdp;
 600 }
 601 URCU_ATTR_ALIAS(urcu_stringify(get_default_call_rcu_data))
 602 struct call_rcu_data *alias_get_default_call_rcu_data();
 603
 604 /*
 605  * Return the call_rcu_data structure that applies to the currently
 606  * running thread.  Any call_rcu_data structure assigned specifically
 607  * to this thread has first priority, followed by any call_rcu_data
 608  * structure assigned to the CPU on which the thread is running,
 609  * followed by the default call_rcu_data structure.  If there is not
 610  * yet a default call_rcu_data structure, one will be created.
 611  *
 612  * Calls to this function and use of the returned call_rcu_data should
 613  * be protected by RCU read-side lock.
 614  */
 615 struct call_rcu_data *get_call_rcu_data(void)
 616 {
 617         struct call_rcu_data *crd;
 618
 619         if (URCU_TLS(thread_call_rcu_data) != NULL)
 620                 return URCU_TLS(thread_call_rcu_data);
 621
 622         if (cpus_array_len > 0) {
 623                 crd = get_cpu_call_rcu_data(urcu_sched_getcpu());
 624                 if (crd)
 625                         return crd;
 626         }
 627
 628         return get_default_call_rcu_data();
 629 }
 630 URCU_ATTR_ALIAS(urcu_stringify(get_call_rcu_data))
 631 struct call_rcu_data *alias_get_call_rcu_data();
 632
 633 /*
 634  * Return a pointer to this task's call_rcu_data if there is one.
 635  */
 636
 637 struct call_rcu_data *get_thread_call_rcu_data(void)
 638 {
 639         return URCU_TLS(thread_call_rcu_data);
 640 }
 641 URCU_ATTR_ALIAS(urcu_stringify(get_thread_call_rcu_data))
 642 struct call_rcu_data *alias_get_thread_call_rcu_data();
 643
 644 /*
 645  * Set this task's call_rcu_data structure as specified, regardless
 646  * of whether or not this task already had one.  (This allows switching
 647  * to and from real-time call_rcu threads, for example.)
 648  *
 649  * Use NULL to remove a thread's call_rcu_data structure, but it is
 650  * the caller's responsibility to dispose of the removed structure.
 651  * Use get_thread_call_rcu_data() to obtain a pointer to the old structure
 652  * (prior to NULLing it out, of course).
 653  */
 654
 655 void set_thread_call_rcu_data(struct call_rcu_data *crdp)
 656 {
 657         URCU_TLS(thread_call_rcu_data) = crdp;
 658 }
 659 URCU_ATTR_ALIAS(urcu_stringify(set_thread_call_rcu_data))
 660 void alias_set_thread_call_rcu_data();
 661
 662 /*
 663  * Create a separate call_rcu thread for each CPU.  This does not
 664  * replace a pre-existing call_rcu thread -- use the set_cpu_call_rcu_data()
 665  * function if you want that behavior. Should be paired with
 666  * free_all_cpu_call_rcu_data() to teardown these call_rcu worker
 667  * threads.
 668  */
 669
 670 int create_all_cpu_call_rcu_data(unsigned long flags)
 671 {
 672         int i;
 673         struct call_rcu_data *crdp;
 674         int ret;
 675
 676         call_rcu_lock(&call_rcu_mutex);
 677         alloc_cpu_call_rcu_data();
 678         call_rcu_unlock(&call_rcu_mutex);
 679         if (cpus_array_len <= 0) {
 680                 errno = EINVAL;
 681                 return -EINVAL;
 682         }
 683         if (per_cpu_call_rcu_data == NULL) {
 684                 errno = ENOMEM;
 685                 return -ENOMEM;
 686         }
 687         for (i = 0; i < cpus_array_len; i++) {
 688                 call_rcu_lock(&call_rcu_mutex);
 689                 if (get_cpu_call_rcu_data(i)) {
 690                         call_rcu_unlock(&call_rcu_mutex);
 691                         continue;
 692                 }
 693                 crdp = __create_call_rcu_data(flags, i);
 694                 if (crdp == NULL) {
 695                         call_rcu_unlock(&call_rcu_mutex);
 696                         errno = ENOMEM;
 697                         return -ENOMEM;
 698                 }
 699                 call_rcu_unlock(&call_rcu_mutex);
 700                 if ((ret = set_cpu_call_rcu_data(i, crdp)) != 0) {
 701                         call_rcu_data_free(crdp);
 702
 703                         /* it has been created by other thread */
 704                         if (ret == -EEXIST)
 705                                 continue;
 706
 707                         return ret;
 708                 }
 709         }
 710         return 0;
 711 }
 712 URCU_ATTR_ALIAS(urcu_stringify(create_all_cpu_call_rcu_data))
 713 int alias_create_all_cpu_call_rcu_data();
 714
 715 /*
 716  * Wake up the call_rcu thread corresponding to the specified
 717  * call_rcu_data structure.
 718  */
 719 static void wake_call_rcu_thread(struct call_rcu_data *crdp)
 720 {
 721         if (!(_CMM_LOAD_SHARED(crdp->flags) & URCU_CALL_RCU_RT))
 722                 call_rcu_wake_up(crdp);
 723 }
 724
 725 static void _call_rcu(struct rcu_head *head,
 726                       void (*func)(struct rcu_head *head),
 727                       struct call_rcu_data *crdp)
 728 {
 729         cds_wfcq_node_init(&head->next);
 730         head->func = func;
 731         cds_wfcq_enqueue(&crdp->cbs_head, &crdp->cbs_tail, &head->next);
 732         uatomic_inc(&crdp->qlen);
 733         wake_call_rcu_thread(crdp);
 734 }
 735
 736 /*
 737  * Schedule a function to be invoked after a following grace period.
 738  * This is the only function that must be called -- the others are
 739  * only present to allow applications to tune their use of RCU for
 740  * maximum performance.
 741  *
 742  * Note that unless a call_rcu thread has not already been created,
 743  * the first invocation of call_rcu() will create one.  So, if you
 744  * need the first invocation of call_rcu() to be fast, make sure
 745  * to create a call_rcu thread first.  One way to accomplish this is
 746  * "get_call_rcu_data();", and another is create_all_cpu_call_rcu_data().
 747  *
 748  * call_rcu must be called by registered RCU read-side threads.
 749  */
 750 void call_rcu(struct rcu_head *head,
 751               void (*func)(struct rcu_head *head))
 752 {
 753         struct call_rcu_data *crdp;
 754
 755         /* Holding rcu read-side lock across use of per-cpu crdp */
 756         _rcu_read_lock();
 757         crdp = get_call_rcu_data();
 758         _call_rcu(head, func, crdp);
 759         _rcu_read_unlock();
 760 }
 761 URCU_ATTR_ALIAS(urcu_stringify(call_rcu)) void alias_call_rcu();
 762
 763 /*
 764  * Free up the specified call_rcu_data structure, terminating the
 765  * associated call_rcu thread.  The caller must have previously
 766  * removed the call_rcu_data structure from per-thread or per-CPU
 767  * usage.  For example, set_cpu_call_rcu_data(cpu, NULL) for per-CPU
 768  * call_rcu_data structures or set_thread_call_rcu_data(NULL) for
 769  * per-thread call_rcu_data structures.
 770  *
 771  * We silently refuse to free up the default call_rcu_data structure
 772  * because that is where we put any leftover callbacks.  Note that
 773  * the possibility of self-spawning callbacks makes it impossible
 774  * to execute all the callbacks in finite time without putting any
 775  * newly spawned callbacks somewhere else.  The "somewhere else" of
 776  * last resort is the default call_rcu_data structure.
 777  *
 778  * We also silently refuse to free NULL pointers.  This simplifies
 779  * the calling code.
 780  *
 781  * The caller must wait for a grace-period to pass between return from
 782  * set_cpu_call_rcu_data() and call to call_rcu_data_free() passing the
 783  * previous call rcu data as argument.
 784  *
 785  * Note: introducing __cds_wfcq_splice_blocking() in this function fixed
 786  * a list corruption bug in the 0.7.x series. The equivalent fix
 787  * appeared in 0.6.8 for the stable-0.6 branch.
 788  */
 789 static
 790 void _call_rcu_data_free(struct call_rcu_data *crdp, unsigned int flags)
 791 {
 792         if (crdp == NULL || crdp == default_call_rcu_data) {
 793                 return;
 794         }
 795         if ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0) {
 796                 uatomic_or(&crdp->flags, URCU_CALL_RCU_STOP);
 797                 wake_call_rcu_thread(crdp);
 798                 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0)
 799                         (void) poll(NULL, 0, 1);
 800         }
 801         call_rcu_lock(&call_rcu_mutex);
 802         if (!cds_wfcq_empty(&crdp->cbs_head, &crdp->cbs_tail)) {
 803                 call_rcu_unlock(&call_rcu_mutex);
 804                 /* Create default call rcu data if need be. */
 805                 /* CBs queued here will be handed to the default list. */
 806                 (void) get_default_call_rcu_data();
 807                 call_rcu_lock(&call_rcu_mutex);
 808                 __cds_wfcq_splice_blocking(&default_call_rcu_data->cbs_head,
 809                         &default_call_rcu_data->cbs_tail,
 810                         &crdp->cbs_head, &crdp->cbs_tail);
 811                 uatomic_add(&default_call_rcu_data->qlen,
 812                             uatomic_read(&crdp->qlen));
 813                 wake_call_rcu_thread(default_call_rcu_data);
 814         }
 815
 816         cds_list_del(&crdp->list);
 817         call_rcu_unlock(&call_rcu_mutex);
 818
 819         if (flags & CRDF_FLAG_JOIN_THREAD) {
 820                 int ret;
 821
 822                 ret = pthread_join(get_call_rcu_thread(crdp), NULL);
 823                 if (ret)
 824                         urcu_die(ret);
 825         }
 826         free(crdp);
 827 }
 828 URCU_ATTR_ALIAS(urcu_stringify(call_rcu_data_free))
 829 void alias_call_rcu_data_free();
 830
 831 void call_rcu_data_free(struct call_rcu_data *crdp)
 832 {
 833         _call_rcu_data_free(crdp, CRDF_FLAG_JOIN_THREAD);
 834 }
 835
 836 /*
 837  * Clean up all the per-CPU call_rcu threads.
 838  */
 839 void free_all_cpu_call_rcu_data(void)
 840 {
 841         int cpu;
 842         struct call_rcu_data **crdp;
 843         static int warned = 0;
 844
 845         if (cpus_array_len <= 0)
 846                 return;
 847
 848         crdp = malloc(sizeof(*crdp) * cpus_array_len);
 849         if (!crdp) {
 850                 if (!warned) {
 851                         fprintf(stderr, "[error] liburcu: unable to allocate per-CPU pointer array\n");
 852                 }
 853                 warned = 1;
 854                 return;
 855         }
 856
 857         for (cpu = 0; cpu < cpus_array_len; cpu++) {
 858                 crdp[cpu] = get_cpu_call_rcu_data(cpu);
 859                 if (crdp[cpu] == NULL)
 860                         continue;
 861                 set_cpu_call_rcu_data(cpu, NULL);
 862         }
 863         /*
 864          * Wait for call_rcu sites acting as RCU readers of the
 865          * call_rcu_data to become quiescent.
 866          */
 867         synchronize_rcu();
 868         for (cpu = 0; cpu < cpus_array_len; cpu++) {
 869                 if (crdp[cpu] == NULL)
 870                         continue;
 871                 call_rcu_data_free(crdp[cpu]);
 872         }
 873         free(crdp);
 874 }
 875 #ifdef RCU_QSBR
 876 /* ABI6 has a non-namespaced free_all_cpu_call_rcu_data for qsbr */
 877 #undef free_all_cpu_call_rcu_data
 878 URCU_ATTR_ALIAS("urcu_qsbr_free_all_cpu_call_rcu_data")
 879 void free_all_cpu_call_rcu_data();
 880 #define free_all_cpu_call_rcu_data urcu_qsbr_free_all_cpu_call_rcu_data
 881 #else
 882 URCU_ATTR_ALIAS(urcu_stringify(free_all_cpu_call_rcu_data))
 883 void alias_free_all_cpu_call_rcu_data();
 884 #endif
 885
 886 static
 887 void free_completion(struct urcu_ref *ref)
 888 {
 889         struct call_rcu_completion *completion;
 890
 891         completion = caa_container_of(ref, struct call_rcu_completion, ref);
 892         free(completion);
 893 }
 894
 895 static
 896 void _rcu_barrier_complete(struct rcu_head *head)
 897 {
 898         struct call_rcu_completion_work *work;
 899         struct call_rcu_completion *completion;
 900
 901         work = caa_container_of(head, struct call_rcu_completion_work, head);
 902         completion = work->completion;
 903         if (!uatomic_sub_return(&completion->barrier_count, 1))
 904                 call_rcu_completion_wake_up(completion);
 905         urcu_ref_put(&completion->ref, free_completion);
 906         free(work);
 907 }
 908
 909 /*
 910  * Wait for all in-flight call_rcu callbacks to complete execution.
 911  */
 912 void rcu_barrier(void)
 913 {
 914         struct call_rcu_data *crdp;
 915         struct call_rcu_completion *completion;
 916         int count = 0;
 917         int was_online;
 918
 919         /* Put in offline state in QSBR. */
 920         was_online = _rcu_read_ongoing();
 921         if (was_online)
 922                 rcu_thread_offline();
 923         /*
 924          * Calling a rcu_barrier() within a RCU read-side critical
 925          * section is an error.
 926          */
 927         if (_rcu_read_ongoing()) {
 928                 static int warned = 0;
 929
 930                 if (!warned) {
 931                         fprintf(stderr, "[error] liburcu: rcu_barrier() called from within RCU read-side critical section.\n");
 932                 }
 933                 warned = 1;
 934                 goto online;
 935         }
 936
 937         completion = calloc(sizeof(*completion), 1);
 938         if (!completion)
 939                 urcu_die(errno);
 940
 941         call_rcu_lock(&call_rcu_mutex);
 942         cds_list_for_each_entry(crdp, &call_rcu_data_list, list)
 943                 count++;
 944
 945         /* Referenced by rcu_barrier() and each call_rcu thread. */
 946         urcu_ref_set(&completion->ref, count + 1);
 947         completion->barrier_count = count;
 948
 949         cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
 950                 struct call_rcu_completion_work *work;
 951
 952                 work = calloc(sizeof(*work), 1);
 953                 if (!work)
 954                         urcu_die(errno);
 955                 work->completion = completion;
 956                 _call_rcu(&work->head, _rcu_barrier_complete, crdp);
 957         }
 958         call_rcu_unlock(&call_rcu_mutex);
 959
 960         /* Wait for them */
 961         for (;;) {
 962                 uatomic_dec(&completion->futex);
 963                 /* Decrement futex before reading barrier_count */
 964                 cmm_smp_mb();
 965                 if (!uatomic_read(&completion->barrier_count))
 966                         break;
 967                 call_rcu_completion_wait(completion);
 968         }
 969
 970         urcu_ref_put(&completion->ref, free_completion);
 971
 972 online:
 973         if (was_online)
 974                 rcu_thread_online();
 975 }
 976 URCU_ATTR_ALIAS(urcu_stringify(rcu_barrier))
 977 void alias_rcu_barrier();
 978
 979 /*
 980  * Acquire the call_rcu_mutex in order to ensure that the child sees
 981  * all of the call_rcu() data structures in a consistent state. Ensure
 982  * that all call_rcu threads are in a quiescent state across fork.
 983  * Suitable for pthread_atfork() and friends.
 984  */
 985 void call_rcu_before_fork(void)
 986 {
 987         struct call_rcu_data *crdp;
 988         struct urcu_atfork *atfork;
 989
 990         call_rcu_lock(&call_rcu_mutex);
 991
 992         atfork = registered_rculfhash_atfork;
 993         if (atfork)
 994                 atfork->before_fork(atfork->priv);
 995
 996         cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
 997                 uatomic_or(&crdp->flags, URCU_CALL_RCU_PAUSE);
 998                 cmm_smp_mb__after_uatomic_or();
 999                 wake_call_rcu_thread(crdp);
1000         }
1001         cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
1002                 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSED) == 0)
1003                         (void) poll(NULL, 0, 1);
1004         }
1005 }
1006 URCU_ATTR_ALIAS(urcu_stringify(call_rcu_before_fork))
1007 void alias_call_rcu_before_fork();
1008
1009 /*
1010  * Clean up call_rcu data structures in the parent of a successful fork()
1011  * that is not followed by exec() in the child.  Suitable for
1012  * pthread_atfork() and friends.
1013  */
1014 void call_rcu_after_fork_parent(void)
1015 {
1016         struct call_rcu_data *crdp;
1017         struct urcu_atfork *atfork;
1018
1019         cds_list_for_each_entry(crdp, &call_rcu_data_list, list)
1020                 uatomic_and(&crdp->flags, ~URCU_CALL_RCU_PAUSE);
1021         cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
1022                 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSED) != 0)
1023                         (void) poll(NULL, 0, 1);
1024         }
1025         atfork = registered_rculfhash_atfork;
1026         if (atfork)
1027                 atfork->after_fork_parent(atfork->priv);
1028         call_rcu_unlock(&call_rcu_mutex);
1029 }
1030 URCU_ATTR_ALIAS(urcu_stringify(call_rcu_after_fork_parent))
1031 void alias_call_rcu_after_fork_parent();
1032
1033 /*
1034  * Clean up call_rcu data structures in the child of a successful fork()
1035  * that is not followed by exec().  Suitable for pthread_atfork() and
1036  * friends.
1037  */
1038 void call_rcu_after_fork_child(void)
1039 {
1040         struct call_rcu_data *crdp, *next;
1041         struct urcu_atfork *atfork;
1042
1043         /* Release the mutex. */
1044         call_rcu_unlock(&call_rcu_mutex);
1045
1046         atfork = registered_rculfhash_atfork;
1047         if (atfork)
1048                 atfork->after_fork_child(atfork->priv);
1049
1050         /* Do nothing when call_rcu() has not been used */
1051         if (cds_list_empty(&call_rcu_data_list))
1052                 return;
1053
1054         /*
1055          * Allocate a new default call_rcu_data structure in order
1056          * to get a working call_rcu thread to go with it.
1057          */
1058         default_call_rcu_data = NULL;
1059         (void)get_default_call_rcu_data();
1060
1061         /* Cleanup call_rcu_data pointers before use */
1062         cpus_array_len_reset();
1063         free(per_cpu_call_rcu_data);
1064         rcu_set_pointer(&per_cpu_call_rcu_data, NULL);
1065         URCU_TLS(thread_call_rcu_data) = NULL;
1066
1067         /*
1068          * Dispose of all of the rest of the call_rcu_data structures.
1069          * Leftover call_rcu callbacks will be merged into the new
1070          * default call_rcu thread queue.
1071          */
1072         cds_list_for_each_entry_safe(crdp, next, &call_rcu_data_list, list) {
1073                 if (crdp == default_call_rcu_data)
1074                         continue;
1075                 uatomic_set(&crdp->flags, URCU_CALL_RCU_STOPPED);
1076                 /*
1077                  * Do not join the thread because it does not exist in
1078                  * the child.
1079                  */
1080                 _call_rcu_data_free(crdp, 0);
1081         }
1082 }
1083 URCU_ATTR_ALIAS(urcu_stringify(call_rcu_after_fork_child))
1084 void alias_call_rcu_after_fork_child();
1085
1086 void urcu_register_rculfhash_atfork(struct urcu_atfork *atfork)
1087 {
1088         if (CMM_LOAD_SHARED(registered_rculfhash_atfork))
1089                 return;
1090         call_rcu_lock(&call_rcu_mutex);
1091         if (!registered_rculfhash_atfork)
1092                 registered_rculfhash_atfork = atfork;
1093         call_rcu_unlock(&call_rcu_mutex);
1094 }
1095 URCU_ATTR_ALIAS(urcu_stringify(urcu_register_rculfhash_atfork))
1096 void alias_urcu_register_rculfhash_atfork();
1097
1098 /*
1099  * This unregistration function is deprecated, meant only for internal
1100  * use by rculfhash.
1101  */
1102 __attribute__((noreturn))
1103 void urcu_unregister_rculfhash_atfork(struct urcu_atfork *atfork __attribute__((unused)))
1104 {
1105         urcu_die(EPERM);
1106 }
1107
1108 URCU_ATTR_ALIAS(urcu_stringify(urcu_unregister_rculfhash_atfork))
1109 __attribute__((noreturn))
1110 void alias_urcu_unregister_rculfhash_atfork();
1111
1112 /*
1113  * Teardown the default call_rcu worker thread if there are no queued
1114  * callbacks on process exit. This prevents leaking memory.
1115  *
1116  * Here is how an application can ensure graceful teardown of this
1117  * worker thread:
1118  *
1119  * - An application queuing call_rcu callbacks should invoke
1120  *   rcu_barrier() before it exits.
1121  * - When chaining call_rcu callbacks, the number of calls to
1122  *   rcu_barrier() on application exit must match at least the maximum
1123  *   number of chained callbacks.
1124  * - If an application chains callbacks endlessly, it would have to be
1125  *   modified to stop chaining callbacks when it detects an application
1126  *   exit (e.g. with a flag), and wait for quiescence with rcu_barrier()
1127  *   after setting that flag.
1128  * - The statements above apply to a library which queues call_rcu
1129  *   callbacks, only it needs to invoke rcu_barrier in its library
1130  *   destructor.
1131  *
1132  * Note that this function does not presume it is being called when the
1133  * application is single-threaded even though this is invoked from a
1134  * destructor: this function synchronizes against concurrent calls to
1135  * get_default_call_rcu_data().
1136  */
1137 static void urcu_call_rcu_exit(void)
1138 {
1139         struct call_rcu_data *crdp;
1140         bool teardown = true;
1141
1142         if (default_call_rcu_data == NULL)
1143                 return;
1144         call_rcu_lock(&call_rcu_mutex);
1145         /*
1146          * If the application leaves callbacks in the default call_rcu
1147          * worker queue, keep the default worker in place.
1148          */
1149         crdp = default_call_rcu_data;
1150         if (!crdp) {
1151                 teardown = false;
1152                 goto unlock;
1153         }
1154         if (!cds_wfcq_empty(&crdp->cbs_head, &crdp->cbs_tail)) {
1155                 teardown = false;
1156                 goto unlock;
1157         }
1158         rcu_set_pointer(&default_call_rcu_data, NULL);
1159 unlock:
1160         call_rcu_unlock(&call_rcu_mutex);
1161         if (teardown) {
1162                 synchronize_rcu();
1163                 call_rcu_data_free(crdp);
1164         }
1165 }