workqueue.c

   1 /*
   2  * workqueue.c
   3  *
   4  * Userspace RCU library - Userspace workqeues
   5  *
   6  * Copyright (c) 2010 Paul E. McKenney <paulmck@linux.vnet.ibm.com>
   7  * Copyright (c) 2017 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   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
  24 #define _LGPL_SOURCE
  25 #define _GNU_SOURCE
  26 #include <stdio.h>
  27 #include <pthread.h>
  28 #include <signal.h>
  29 #include <assert.h>
  30 #include <stdlib.h>
  31 #include <stdint.h>
  32 #include <string.h>
  33 #include <errno.h>
  34 #include <poll.h>
  35 #include <sys/time.h>
  36 #include <unistd.h>
  37 #include <sched.h>
  38
  39 #include "compat-getcpu.h"
  40 #include "urcu/wfcqueue.h"
  41 #include "urcu-call-rcu.h"
  42 #include "urcu-pointer.h"
  43 #include "urcu/list.h"
  44 #include "urcu/futex.h"
  45 #include "urcu/tls-compat.h"
  46 #include "urcu/ref.h"
  47 #include "urcu-die.h"
  48
  49 #include "workqueue.h"
  50
  51 #define SET_AFFINITY_CHECK_PERIOD               (1U << 8)       /* 256 */
  52 #define SET_AFFINITY_CHECK_PERIOD_MASK          (SET_AFFINITY_CHECK_PERIOD - 1)
  53
  54 /* Data structure that identifies a workqueue. */
  55
  56 struct urcu_workqueue {
  57         /*
  58          * We do not align head on a different cache-line than tail
  59          * mainly because call_rcu callback-invocation threads use
  60          * batching ("splice") to get an entire list of callbacks, which
  61          * effectively empties the queue, and requires to touch the tail
  62          * anyway.
  63          */
  64         struct cds_wfcq_tail cbs_tail;
  65         struct cds_wfcq_head cbs_head;
  66         unsigned long flags;
  67         int32_t futex;
  68         unsigned long qlen; /* maintained for debugging. */
  69         pthread_t tid;
  70         int cpu_affinity;
  71         unsigned long loop_count;
  72         void *priv;
  73         void (*grace_period_fct)(struct urcu_workqueue *workqueue, void *priv);
  74         void (*initialize_worker_fct)(struct urcu_workqueue *workqueue, void *priv);
  75         void (*finalize_worker_fct)(struct urcu_workqueue *workqueue, void *priv);
  76         void (*worker_before_pause_fct)(struct urcu_workqueue *workqueue, void *priv);
  77         void (*worker_after_resume_fct)(struct urcu_workqueue *workqueue, void *priv);
  78         void (*worker_before_wait_fct)(struct urcu_workqueue *workqueue, void *priv);
  79         void (*worker_after_wake_up_fct)(struct urcu_workqueue *workqueue, void *priv);
  80 } __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
  81
  82 struct urcu_workqueue_completion {
  83         int barrier_count;
  84         int32_t futex;
  85         struct urcu_ref ref;
  86 };
  87
  88 struct urcu_workqueue_completion_work {
  89         struct urcu_work work;
  90         struct urcu_workqueue_completion *completion;
  91 };
  92
  93 /*
  94  * Periodically retry setting CPU affinity if we migrate.
  95  * Losing affinity can be caused by CPU hotunplug/hotplug, or by
  96  * cpuset(7).
  97  */
  98 #if HAVE_SCHED_SETAFFINITY
  99 static int set_thread_cpu_affinity(struct urcu_workqueue *workqueue)
 100 {
 101         cpu_set_t mask;
 102         int ret;
 103
 104         if (workqueue->cpu_affinity < 0)
 105                 return 0;
 106         if (++workqueue->loop_count & SET_AFFINITY_CHECK_PERIOD_MASK)
 107                 return 0;
 108         if (urcu_sched_getcpu() == workqueue->cpu_affinity)
 109                 return 0;
 110
 111         CPU_ZERO(&mask);
 112         CPU_SET(workqueue->cpu_affinity, &mask);
 113 #if SCHED_SETAFFINITY_ARGS == 2
 114         ret = sched_setaffinity(0, &mask);
 115 #else
 116         ret = sched_setaffinity(0, sizeof(mask), &mask);
 117 #endif
 118         /*
 119          * EINVAL is fine: can be caused by hotunplugged CPUs, or by
 120          * cpuset(7). This is why we should always retry if we detect
 121          * migration.
 122          */
 123         if (ret && errno == EINVAL) {
 124                 ret = 0;
 125                 errno = 0;
 126         }
 127         return ret;
 128 }
 129 #else
 130 static int set_thread_cpu_affinity(struct urcu_workqueue *workqueue)
 131 {
 132         return 0;
 133 }
 134 #endif
 135
 136 static void futex_wait(int32_t *futex)
 137 {
 138         /* Read condition before read futex */
 139         cmm_smp_mb();
 140         if (uatomic_read(futex) != -1)
 141                 return;
 142         while (futex_async(futex, FUTEX_WAIT, -1, NULL, NULL, 0)) {
 143                 switch (errno) {
 144                 case EWOULDBLOCK:
 145                         /* Value already changed. */
 146                         return;
 147                 case EINTR:
 148                         /* Retry if interrupted by signal. */
 149                         break;  /* Get out of switch. */
 150                 default:
 151                         /* Unexpected error. */
 152                         urcu_die(errno);
 153                 }
 154         }
 155 }
 156
 157 static void futex_wake_up(int32_t *futex)
 158 {
 159         /* Write to condition before reading/writing futex */
 160         cmm_smp_mb();
 161         if (caa_unlikely(uatomic_read(futex) == -1)) {
 162                 uatomic_set(futex, 0);
 163                 if (futex_async(futex, FUTEX_WAKE, 1,
 164                                 NULL, NULL, 0) < 0)
 165                         urcu_die(errno);
 166         }
 167 }
 168
 169 /* This is the code run by each worker thread. */
 170
 171 static void *workqueue_thread(void *arg)
 172 {
 173         unsigned long cbcount;
 174         struct urcu_workqueue *workqueue = (struct urcu_workqueue *) arg;
 175         int rt = !!(uatomic_read(&workqueue->flags) & URCU_WORKQUEUE_RT);
 176
 177         if (set_thread_cpu_affinity(workqueue))
 178                 urcu_die(errno);
 179
 180         if (workqueue->initialize_worker_fct)
 181                 workqueue->initialize_worker_fct(workqueue, workqueue->priv);
 182
 183         if (!rt) {
 184                 uatomic_dec(&workqueue->futex);
 185                 /* Decrement futex before reading workqueue */
 186                 cmm_smp_mb();
 187         }
 188         for (;;) {
 189                 struct cds_wfcq_head cbs_tmp_head;
 190                 struct cds_wfcq_tail cbs_tmp_tail;
 191                 struct cds_wfcq_node *cbs, *cbs_tmp_n;
 192                 enum cds_wfcq_ret splice_ret;
 193
 194                 if (set_thread_cpu_affinity(workqueue))
 195                         urcu_die(errno);
 196
 197                 if (uatomic_read(&workqueue->flags) & URCU_WORKQUEUE_PAUSE) {
 198                         /*
 199                          * Pause requested. Become quiescent: remove
 200                          * ourself from all global lists, and don't
 201                          * process any callback. The callback lists may
 202                          * still be non-empty though.
 203                          */
 204                         if (workqueue->worker_before_pause_fct)
 205                                 workqueue->worker_before_pause_fct(workqueue, workqueue->priv);
 206                         cmm_smp_mb__before_uatomic_or();
 207                         uatomic_or(&workqueue->flags, URCU_WORKQUEUE_PAUSED);
 208                         while ((uatomic_read(&workqueue->flags) & URCU_WORKQUEUE_PAUSE) != 0)
 209                                 (void) poll(NULL, 0, 1);
 210                         uatomic_and(&workqueue->flags, ~URCU_WORKQUEUE_PAUSED);
 211                         cmm_smp_mb__after_uatomic_and();
 212                         if (workqueue->worker_after_resume_fct)
 213                                 workqueue->worker_after_resume_fct(workqueue, workqueue->priv);
 214                 }
 215
 216                 cds_wfcq_init(&cbs_tmp_head, &cbs_tmp_tail);
 217                 splice_ret = __cds_wfcq_splice_blocking(&cbs_tmp_head,
 218                         &cbs_tmp_tail, &workqueue->cbs_head, &workqueue->cbs_tail);
 219                 assert(splice_ret != CDS_WFCQ_RET_WOULDBLOCK);
 220                 assert(splice_ret != CDS_WFCQ_RET_DEST_NON_EMPTY);
 221                 if (splice_ret != CDS_WFCQ_RET_SRC_EMPTY) {
 222                         if (workqueue->grace_period_fct)
 223                                 workqueue->grace_period_fct(workqueue, workqueue->priv);
 224                         cbcount = 0;
 225                         __cds_wfcq_for_each_blocking_safe(&cbs_tmp_head,
 226                                         &cbs_tmp_tail, cbs, cbs_tmp_n) {
 227                                 struct rcu_head *rhp;
 228
 229                                 rhp = caa_container_of(cbs,
 230                                         struct rcu_head, next);
 231                                 rhp->func(rhp);
 232                                 cbcount++;
 233                         }
 234                         uatomic_sub(&workqueue->qlen, cbcount);
 235                 }
 236                 if (uatomic_read(&workqueue->flags) & URCU_WORKQUEUE_STOP)
 237                         break;
 238                 if (workqueue->worker_before_wait_fct)
 239                         workqueue->worker_before_wait_fct(workqueue, workqueue->priv);
 240                 if (!rt) {
 241                         if (cds_wfcq_empty(&workqueue->cbs_head,
 242                                         &workqueue->cbs_tail)) {
 243                                 futex_wait(&workqueue->futex);
 244                                 (void) poll(NULL, 0, 10);
 245                                 uatomic_dec(&workqueue->futex);
 246                                 /*
 247                                  * Decrement futex before reading
 248                                  * call_rcu list.
 249                                  */
 250                                 cmm_smp_mb();
 251                         } else {
 252                                 (void) poll(NULL, 0, 10);
 253                         }
 254                 } else {
 255                         (void) poll(NULL, 0, 10);
 256                 }
 257                 if (workqueue->worker_after_wake_up_fct)
 258                         workqueue->worker_after_wake_up_fct(workqueue, workqueue->priv);
 259         }
 260         if (!rt) {
 261                 /*
 262                  * Read call_rcu list before write futex.
 263                  */
 264                 cmm_smp_mb();
 265                 uatomic_set(&workqueue->futex, 0);
 266         }
 267         if (workqueue->finalize_worker_fct)
 268                 workqueue->finalize_worker_fct(workqueue, workqueue->priv);
 269         return NULL;
 270 }
 271
 272 struct urcu_workqueue *urcu_workqueue_create(unsigned long flags,
 273                 int cpu_affinity, void *priv,
 274                 void (*grace_period_fct)(struct urcu_workqueue *workqueue, void *priv),
 275                 void (*initialize_worker_fct)(struct urcu_workqueue *workqueue, void *priv),
 276                 void (*finalize_worker_fct)(struct urcu_workqueue *workqueue, void *priv),
 277                 void (*worker_before_wait_fct)(struct urcu_workqueue *workqueue, void *priv),
 278                 void (*worker_after_wake_up_fct)(struct urcu_workqueue *workqueue, void *priv),
 279                 void (*worker_before_pause_fct)(struct urcu_workqueue *workqueue, void *priv),
 280                 void (*worker_after_resume_fct)(struct urcu_workqueue *workqueue, void *priv))
 281 {
 282         struct urcu_workqueue *workqueue;
 283         int ret;
 284
 285         workqueue = malloc(sizeof(*workqueue));
 286         if (workqueue == NULL)
 287                 urcu_die(errno);
 288         memset(workqueue, '\0', sizeof(*workqueue));
 289         cds_wfcq_init(&workqueue->cbs_head, &workqueue->cbs_tail);
 290         workqueue->qlen = 0;
 291         workqueue->futex = 0;
 292         workqueue->flags = flags;
 293         workqueue->priv = priv;
 294         workqueue->grace_period_fct = grace_period_fct;
 295         workqueue->initialize_worker_fct = initialize_worker_fct;
 296         workqueue->finalize_worker_fct = finalize_worker_fct;
 297         workqueue->worker_before_wait_fct = worker_before_wait_fct;
 298         workqueue->worker_after_wake_up_fct = worker_after_wake_up_fct;
 299         workqueue->worker_before_pause_fct = worker_before_pause_fct;
 300         workqueue->worker_after_resume_fct = worker_after_resume_fct;
 301         workqueue->cpu_affinity = cpu_affinity;
 302         workqueue->loop_count = 0;
 303         cmm_smp_mb();  /* Structure initialized before pointer is planted. */
 304         ret = pthread_create(&workqueue->tid, NULL, workqueue_thread, workqueue);
 305         if (ret) {
 306                 urcu_die(ret);
 307         }
 308         return workqueue;
 309 }
 310
 311 static void wake_worker_thread(struct urcu_workqueue *workqueue)
 312 {
 313         if (!(_CMM_LOAD_SHARED(workqueue->flags) & URCU_CALL_RCU_RT))
 314                 futex_wake_up(&workqueue->futex);
 315 }
 316
 317 static int urcu_workqueue_destroy_worker(struct urcu_workqueue *workqueue)
 318 {
 319         int ret;
 320         void *retval;
 321
 322         uatomic_or(&workqueue->flags, URCU_WORKQUEUE_STOP);
 323         wake_worker_thread(workqueue);
 324
 325         ret = pthread_join(workqueue->tid, &retval);
 326         if (ret) {
 327                 urcu_die(ret);
 328         }
 329         if (retval != NULL) {
 330                 urcu_die(EINVAL);
 331         }
 332         workqueue->flags &= ~URCU_WORKQUEUE_STOP;
 333         workqueue->tid = 0;
 334         return 0;
 335 }
 336
 337 void urcu_workqueue_destroy(struct urcu_workqueue *workqueue)
 338 {
 339         if (workqueue == NULL) {
 340                 return;
 341         }
 342         if (urcu_workqueue_destroy_worker(workqueue)) {
 343                 urcu_die(errno);
 344         }
 345         assert(cds_wfcq_empty(&workqueue->cbs_head, &workqueue->cbs_tail));
 346         free(workqueue);
 347 }
 348
 349 void urcu_workqueue_queue_work(struct urcu_workqueue *workqueue,
 350                       struct urcu_work *work,
 351                       void (*func)(struct urcu_work *work))
 352 {
 353         cds_wfcq_node_init(&work->next);
 354         work->func = func;
 355         cds_wfcq_enqueue(&workqueue->cbs_head, &workqueue->cbs_tail, &work->next);
 356         uatomic_inc(&workqueue->qlen);
 357         wake_worker_thread(workqueue);
 358 }
 359
 360 static
 361 void free_completion(struct urcu_ref *ref)
 362 {
 363         struct urcu_workqueue_completion *completion;
 364
 365         completion = caa_container_of(ref, struct urcu_workqueue_completion, ref);
 366         free(completion);
 367 }
 368
 369 static
 370 void _urcu_workqueue_wait_complete(struct urcu_work *work)
 371 {
 372         struct urcu_workqueue_completion_work *completion_work;
 373         struct urcu_workqueue_completion *completion;
 374
 375         completion_work = caa_container_of(work, struct urcu_workqueue_completion_work, work);
 376         completion = completion_work->completion;
 377         if (!uatomic_sub_return(&completion->barrier_count, 1))
 378                 futex_wake_up(&completion->futex);
 379         urcu_ref_put(&completion->ref, free_completion);
 380         free(completion_work);
 381 }
 382
 383 struct urcu_workqueue_completion *urcu_workqueue_create_completion(void)
 384 {
 385         struct urcu_workqueue_completion *completion;
 386
 387         completion = calloc(sizeof(*completion), 1);
 388         if (!completion)
 389                 urcu_die(errno);
 390         urcu_ref_set(&completion->ref, 1);
 391         completion->barrier_count = 0;
 392         return completion;
 393 }
 394
 395 void urcu_workqueue_destroy_completion(struct urcu_workqueue_completion *completion)
 396 {
 397         urcu_ref_put(&completion->ref, free_completion);
 398 }
 399
 400 void urcu_workqueue_wait_completion(struct urcu_workqueue_completion *completion)
 401 {
 402         /* Wait for them */
 403         for (;;) {
 404                 uatomic_dec(&completion->futex);
 405                 /* Decrement futex before reading barrier_count */
 406                 cmm_smp_mb();
 407                 if (!uatomic_read(&completion->barrier_count))
 408                         break;
 409                 futex_wait(&completion->futex);
 410         }
 411 }
 412
 413 void urcu_workqueue_queue_completion(struct urcu_workqueue *workqueue,
 414                 struct urcu_workqueue_completion *completion)
 415 {
 416         struct urcu_workqueue_completion_work *work;
 417
 418         work = calloc(sizeof(*work), 1);
 419         if (!work)
 420                 urcu_die(errno);
 421         work->completion = completion;
 422         urcu_ref_get(&completion->ref);
 423         uatomic_inc(&completion->barrier_count);
 424         urcu_workqueue_queue_work(workqueue, &work->work, _urcu_workqueue_wait_complete);
 425 }
 426
 427 /*
 428  * Wait for all in-flight work to complete execution.
 429  */
 430 void urcu_workqueue_flush_queued_work(struct urcu_workqueue *workqueue)
 431 {
 432         struct urcu_workqueue_completion *completion;
 433
 434         completion = urcu_workqueue_create_completion();
 435         if (!completion)
 436                 urcu_die(ENOMEM);
 437         urcu_workqueue_queue_completion(workqueue, completion);
 438         urcu_workqueue_wait_completion(completion);
 439         urcu_workqueue_destroy_completion(completion);
 440 }
 441
 442 /* To be used in before fork handler. */
 443 void urcu_workqueue_pause_worker(struct urcu_workqueue *workqueue)
 444 {
 445         uatomic_or(&workqueue->flags, URCU_WORKQUEUE_PAUSE);
 446         cmm_smp_mb__after_uatomic_or();
 447         wake_worker_thread(workqueue);
 448
 449         while ((uatomic_read(&workqueue->flags) & URCU_WORKQUEUE_PAUSED) == 0)
 450                 (void) poll(NULL, 0, 1);
 451 }
 452
 453 /* To be used in after fork parent handler. */
 454 void urcu_workqueue_resume_worker(struct urcu_workqueue *workqueue)
 455 {
 456         uatomic_and(&workqueue->flags, ~URCU_WORKQUEUE_PAUSE);
 457         while ((uatomic_read(&workqueue->flags) & URCU_WORKQUEUE_PAUSED) != 0)
 458                 (void) poll(NULL, 0, 1);
 459 }
 460
 461 void urcu_workqueue_create_worker(struct urcu_workqueue *workqueue)
 462 {
 463         int ret;
 464
 465         /* Clear workqueue state from parent. */
 466         workqueue->flags &= ~URCU_WORKQUEUE_PAUSED;
 467         workqueue->flags &= ~URCU_WORKQUEUE_PAUSE;
 468         workqueue->tid = 0;
 469         ret = pthread_create(&workqueue->tid, NULL, workqueue_thread, workqueue);
 470         if (ret) {
 471                 urcu_die(ret);
 472         }
 473 }