1 // SPDX-FileCopyrightText: 2010 Paul E. McKenney <paulmck (at) linux.vnet.ibm.com> 2 // SPDX-FileCopyrightText: 2017 Mathieu Desnoyers <mathieu.desnoyers (at) efficios.com> 3 // 4 // SPDX-License-Identifier: LGPL-2.1-or-later 5 6 /* 7 * Userspace RCU library - Userspace workqeues 8 */ 9 10 #define _LGPL_SOURCE 11 #include <stdio.h> 12 #include <pthread.h> 13 #include <signal.h> 14 #include <stdlib.h> 15 #include <stdint.h> 16 #include <string.h> 17 #include <errno.h> 18 #include <poll.h> 19 #include <sys/time.h> 20 #include <unistd.h> 21 #include <sched.h> 22 23 #include "compat-getcpu.h" 24 #include <urcu/assert.h> 25 #include <urcu/wfcqueue.h> 26 #include <urcu/pointer.h> 27 #include <urcu/list.h> 28 #include <urcu/futex.h> 29 #include <urcu/tls-compat.h> 30 #include <urcu/ref.h> 31 #include "urcu-die.h" 32 33 #include "workqueue.h" 34 35 #define SET_AFFINITY_CHECK_PERIOD (1U << 8) /* 256 */ 36 #define SET_AFFINITY_CHECK_PERIOD_MASK (SET_AFFINITY_CHECK_PERIOD - 1) 37 38 /* Data structure that identifies a workqueue. */ 39 40 struct urcu_workqueue { 41 /* 42 * We do not align head on a different cache-line than tail 43 * mainly because workqueue threads use batching ("splice") to 44 * get an entire list of callbacks, which effectively empties 45 * the queue, and requires to touch the tail anyway. 46 */ 47 struct cds_wfcq_tail cbs_tail; 48 struct cds_wfcq_head cbs_head; 49 unsigned long flags; 50 int32_t futex; 51 unsigned long qlen; /* maintained for debugging. */ 52 pthread_t tid; 53 int cpu_affinity; 54 unsigned long loop_count; 55 void *priv; 56 void (*grace_period_fct)(struct urcu_workqueue *workqueue, void *priv); 57 void (*initialize_worker_fct)(struct urcu_workqueue *workqueue, void *priv); 58 void (*finalize_worker_fct)(struct urcu_workqueue *workqueue, void *priv); 59 void (*worker_before_pause_fct)(struct urcu_workqueue *workqueue, void *priv); 60 void (*worker_after_resume_fct)(struct urcu_workqueue *workqueue, void *priv); 61 void (*worker_before_wait_fct)(struct urcu_workqueue *workqueue, void *priv); 62 void (*worker_after_wake_up_fct)(struct urcu_workqueue *workqueue, void *priv); 63 } __attribute__((aligned(CAA_CACHE_LINE_SIZE))); 64 65 struct urcu_workqueue_completion { 66 int barrier_count; 67 int32_t futex; 68 struct urcu_ref ref; 69 }; 70 71 struct urcu_workqueue_completion_work { 72 struct urcu_work work; 73 struct urcu_workqueue_completion *completion; 74 }; 75 76 /* 77 * Periodically retry setting CPU affinity if we migrate. 78 * Losing affinity can be caused by CPU hotunplug/hotplug, or by 79 * cpuset(7). 80 */ 81 #ifdef HAVE_SCHED_SETAFFINITY 82 static int set_thread_cpu_affinity(struct urcu_workqueue *workqueue) 83 { 84 cpu_set_t mask; 85 int ret; 86 87 if (workqueue->cpu_affinity < 0) 88 return 0; 89 if (++workqueue->loop_count & SET_AFFINITY_CHECK_PERIOD_MASK) 90 return 0; 91 if (urcu_sched_getcpu() == workqueue->cpu_affinity) 92 return 0; 93 94 CPU_ZERO(&mask); 95 CPU_SET(workqueue->cpu_affinity, &mask); 96 ret = sched_setaffinity(0, sizeof(mask), &mask); 97 98 /* 99 * EINVAL is fine: can be caused by hotunplugged CPUs, or by 100 * cpuset(7). This is why we should always retry if we detect 101 * migration. 102 */ 103 if (ret && errno == EINVAL) { 104 ret = 0; 105 errno = 0; 106 } 107 return ret; 108 } 109 #else 110 static int set_thread_cpu_affinity(struct urcu_workqueue *workqueue __attribute__((unused))) 111 { 112 return 0; 113 } 114 #endif 115 116 static void futex_wait(int32_t *futex) 117 { 118 /* Read condition before read futex */ 119 cmm_smp_mb(); 120 while (uatomic_read(futex) == -1) { 121 if (!futex_async(futex, FUTEX_WAIT, -1, NULL, NULL, 0)) { 122 /* 123 * Prior queued wakeups queued by unrelated code 124 * using the same address can cause futex wait to 125 * return 0 even through the futex value is still 126 * -1 (spurious wakeups). Check the value again 127 * in user-space to validate whether it really 128 * differs from -1. 129 */ 130 continue; 131 } 132 switch (errno) { 133 case EAGAIN: 134 /* Value already changed. */ 135 return; 136 case EINTR: 137 /* Retry if interrupted by signal. */ 138 break; /* Get out of switch. Check again. */ 139 default: 140 /* Unexpected error. */ 141 urcu_die(errno); 142 } 143 } 144 } 145 146 static void futex_wake_up(int32_t *futex) 147 { 148 /* Write to condition before reading/writing futex */ 149 cmm_smp_mb(); 150 if (caa_unlikely(uatomic_read(futex) == -1)) { 151 uatomic_set(futex, 0); 152 if (futex_async(futex, FUTEX_WAKE, 1, 153 NULL, NULL, 0) < 0) 154 urcu_die(errno); 155 } 156 } 157 158 /* This is the code run by each worker thread. */ 159 160 static void *workqueue_thread(void *arg) 161 { 162 unsigned long cbcount; 163 struct urcu_workqueue *workqueue = (struct urcu_workqueue *) arg; 164 int rt = !!(uatomic_read(&workqueue->flags) & URCU_WORKQUEUE_RT); 165 166 if (set_thread_cpu_affinity(workqueue)) 167 urcu_die(errno); 168 169 if (workqueue->initialize_worker_fct) 170 workqueue->initialize_worker_fct(workqueue, workqueue->priv); 171 172 if (!rt) { 173 uatomic_dec(&workqueue->futex); 174 /* Decrement futex before reading workqueue */ 175 cmm_smp_mb(); 176 } 177 for (;;) { 178 struct cds_wfcq_head cbs_tmp_head; 179 struct cds_wfcq_tail cbs_tmp_tail; 180 struct cds_wfcq_node *cbs, *cbs_tmp_n; 181 enum cds_wfcq_ret splice_ret; 182 183 if (set_thread_cpu_affinity(workqueue)) 184 urcu_die(errno); 185 186 if (uatomic_read(&workqueue->flags) & URCU_WORKQUEUE_PAUSE) { 187 /* 188 * Pause requested. Become quiescent: remove 189 * ourself from all global lists, and don't 190 * process any callback. The callback lists may 191 * still be non-empty though. 192 */ 193 if (workqueue->worker_before_pause_fct) 194 workqueue->worker_before_pause_fct(workqueue, workqueue->priv); 195 cmm_smp_mb__before_uatomic_or(); 196 uatomic_or(&workqueue->flags, URCU_WORKQUEUE_PAUSED); 197 while ((uatomic_read(&workqueue->flags) & URCU_WORKQUEUE_PAUSE) != 0) 198 (void) poll(NULL, 0, 1); 199 uatomic_and(&workqueue->flags, ~URCU_WORKQUEUE_PAUSED); 200 cmm_smp_mb__after_uatomic_and(); 201 if (workqueue->worker_after_resume_fct) 202 workqueue->worker_after_resume_fct(workqueue, workqueue->priv); 203 } 204 205 cds_wfcq_init(&cbs_tmp_head, &cbs_tmp_tail); 206 splice_ret = __cds_wfcq_splice_blocking(&cbs_tmp_head, 207 &cbs_tmp_tail, &workqueue->cbs_head, &workqueue->cbs_tail); 208 urcu_posix_assert(splice_ret != CDS_WFCQ_RET_WOULDBLOCK); 209 urcu_posix_assert(splice_ret != CDS_WFCQ_RET_DEST_NON_EMPTY); 210 if (splice_ret != CDS_WFCQ_RET_SRC_EMPTY) { 211 if (workqueue->grace_period_fct) 212 workqueue->grace_period_fct(workqueue, workqueue->priv); 213 cbcount = 0; 214 __cds_wfcq_for_each_blocking_safe(&cbs_tmp_head, 215 &cbs_tmp_tail, cbs, cbs_tmp_n) { 216 struct urcu_work *uwp; 217 218 uwp = caa_container_of(cbs, 219 struct urcu_work, next); 220 uwp->func(uwp); 221 cbcount++; 222 } 223 uatomic_sub(&workqueue->qlen, cbcount); 224 } 225 if (uatomic_read(&workqueue->flags) & URCU_WORKQUEUE_STOP) 226 break; 227 if (workqueue->worker_before_wait_fct) 228 workqueue->worker_before_wait_fct(workqueue, workqueue->priv); 229 if (!rt) { 230 if (cds_wfcq_empty(&workqueue->cbs_head, 231 &workqueue->cbs_tail)) { 232 futex_wait(&workqueue->futex); 233 uatomic_dec(&workqueue->futex); 234 /* 235 * Decrement futex before reading 236 * urcu_work list. 237 */ 238 cmm_smp_mb(); 239 } 240 } else { 241 if (cds_wfcq_empty(&workqueue->cbs_head, 242 &workqueue->cbs_tail)) { 243 (void) poll(NULL, 0, 10); 244 } 245 } 246 if (workqueue->worker_after_wake_up_fct) 247 workqueue->worker_after_wake_up_fct(workqueue, workqueue->priv); 248 } 249 if (!rt) { 250 /* 251 * Read urcu_work list before write futex. 252 */ 253 cmm_smp_mb(); 254 uatomic_set(&workqueue->futex, 0); 255 } 256 if (workqueue->finalize_worker_fct) 257 workqueue->finalize_worker_fct(workqueue, workqueue->priv); 258 return NULL; 259 } 260 261 struct urcu_workqueue *urcu_workqueue_create(unsigned long flags, 262 int cpu_affinity, void *priv, 263 void (*grace_period_fct)(struct urcu_workqueue *workqueue, void *priv), 264 void (*initialize_worker_fct)(struct urcu_workqueue *workqueue, void *priv), 265 void (*finalize_worker_fct)(struct urcu_workqueue *workqueue, void *priv), 266 void (*worker_before_wait_fct)(struct urcu_workqueue *workqueue, void *priv), 267 void (*worker_after_wake_up_fct)(struct urcu_workqueue *workqueue, void *priv), 268 void (*worker_before_pause_fct)(struct urcu_workqueue *workqueue, void *priv), 269 void (*worker_after_resume_fct)(struct urcu_workqueue *workqueue, void *priv)) 270 { 271 struct urcu_workqueue *workqueue; 272 int ret; 273 sigset_t newmask, oldmask; 274 275 workqueue = malloc(sizeof(*workqueue)); 276 if (workqueue == NULL) 277 urcu_die(errno); 278 memset(workqueue, '\0', sizeof(*workqueue)); 279 cds_wfcq_init(&workqueue->cbs_head, &workqueue->cbs_tail); 280 workqueue->qlen = 0; 281 workqueue->futex = 0; 282 workqueue->flags = flags; 283 workqueue->priv = priv; 284 workqueue->grace_period_fct = grace_period_fct; 285 workqueue->initialize_worker_fct = initialize_worker_fct; 286 workqueue->finalize_worker_fct = finalize_worker_fct; 287 workqueue->worker_before_wait_fct = worker_before_wait_fct; 288 workqueue->worker_after_wake_up_fct = worker_after_wake_up_fct; 289 workqueue->worker_before_pause_fct = worker_before_pause_fct; 290 workqueue->worker_after_resume_fct = worker_after_resume_fct; 291 workqueue->cpu_affinity = cpu_affinity; 292 workqueue->loop_count = 0; 293 cmm_smp_mb(); /* Structure initialized before pointer is planted. */ 294 295 ret = sigfillset(&newmask); 296 urcu_posix_assert(!ret); 297 ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask); 298 urcu_posix_assert(!ret); 299 300 ret = pthread_create(&workqueue->tid, NULL, workqueue_thread, workqueue); 301 if (ret) { 302 urcu_die(ret); 303 } 304 305 ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL); 306 urcu_posix_assert(!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_WORKQUEUE_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 urcu_posix_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(1, sizeof(*completion)); 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(1, sizeof(*work)); 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 sigset_t newmask, oldmask; 465 466 /* Clear workqueue state from parent. */ 467 workqueue->flags &= ~URCU_WORKQUEUE_PAUSED; 468 workqueue->flags &= ~URCU_WORKQUEUE_PAUSE; 469 workqueue->tid = 0; 470 471 ret = sigfillset(&newmask); 472 urcu_posix_assert(!ret); 473 ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask); 474 urcu_posix_assert(!ret); 475 476 ret = pthread_create(&workqueue->tid, NULL, workqueue_thread, workqueue); 477 if (ret) { 478 urcu_die(ret); 479 } 480 481 ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL); 482 urcu_posix_assert(!ret); 483 } 484
Indexes created Tue Jun 16 00:25:01 UTC 2026