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