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sys/kern/subr_epoch.c
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1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (c) 2018, Matthew Macy <mmacy@freebsd.org> 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 25 * SUCH DAMAGE. 26 * 27 */ 28 29 #include <sys/cdefs.h> 30 __FBSDID("$FreeBSD$"); 31 32 #include <sys/param.h> 33 #include <sys/systm.h> 34 #include <sys/counter.h> 35 #include <sys/epoch.h> 36 #include <sys/gtaskqueue.h> 37 #include <sys/kernel.h> 38 #include <sys/limits.h> 39 #include <sys/lock.h> 40 #include <sys/malloc.h> 41 #include <sys/mutex.h> 42 #include <sys/pcpu.h> 43 #include <sys/proc.h> 44 #include <sys/sched.h> 45 #include <sys/sx.h> 46 #include <sys/smp.h> 47 #include <sys/sysctl.h> 48 #include <sys/turnstile.h> 49 #ifdef EPOCH_TRACE 50 #include <machine/stdarg.h> 51 #include <sys/stack.h> 52 #include <sys/tree.h> 53 #endif 54 #include <vm/vm.h> 55 #include <vm/vm_extern.h> 56 #include <vm/vm_kern.h> 57 #include <vm/uma.h> 58 59 #include <ck_epoch.h> 60 61 #ifdef __amd64__ 62 #define EPOCH_ALIGN CACHE_LINE_SIZE*2 63 #else 64 #define EPOCH_ALIGN CACHE_LINE_SIZE 65 #endif 66 67 TAILQ_HEAD (epoch_tdlist, epoch_tracker); 68 typedef struct epoch_record { 69 ck_epoch_record_t er_record; 70 struct epoch_context er_drain_ctx; 71 struct epoch *er_parent; 72 volatile struct epoch_tdlist er_tdlist; 73 volatile uint32_t er_gen; 74 uint32_t er_cpuid; 75 #ifdef INVARIANTS 76 /* Used to verify record ownership for non-preemptible epochs. */ 77 struct thread *er_td; 78 #endif 79 } __aligned(EPOCH_ALIGN) *epoch_record_t; 80 81 struct epoch { 82 struct ck_epoch e_epoch __aligned(EPOCH_ALIGN); 83 epoch_record_t e_pcpu_record; 84 int e_in_use; 85 int e_flags; 86 struct sx e_drain_sx; 87 struct mtx e_drain_mtx; 88 volatile int e_drain_count; 89 const char *e_name; 90 }; 91 92 /* arbitrary --- needs benchmarking */ 93 #define MAX_ADAPTIVE_SPIN 100 94 #define MAX_EPOCHS 64 95 96 CTASSERT(sizeof(ck_epoch_entry_t) == sizeof(struct epoch_context)); 97 SYSCTL_NODE(_kern, OID_AUTO, epoch, CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 98 "epoch information"); 99 SYSCTL_NODE(_kern_epoch, OID_AUTO, stats, CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 100 "epoch stats"); 101 102 /* Stats. */ 103 static counter_u64_t block_count; 104 105 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, nblocked, CTLFLAG_RW, 106 &block_count, "# of times a thread was in an epoch when epoch_wait was called"); 107 static counter_u64_t migrate_count; 108 109 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, migrations, CTLFLAG_RW, 110 &migrate_count, "# of times thread was migrated to another CPU in epoch_wait"); 111 static counter_u64_t turnstile_count; 112 113 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, ncontended, CTLFLAG_RW, 114 &turnstile_count, "# of times a thread was blocked on a lock in an epoch during an epoch_wait"); 115 static counter_u64_t switch_count; 116 117 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, switches, CTLFLAG_RW, 118 &switch_count, "# of times a thread voluntarily context switched in epoch_wait"); 119 static counter_u64_t epoch_call_count; 120 121 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, epoch_calls, CTLFLAG_RW, 122 &epoch_call_count, "# of times a callback was deferred"); 123 static counter_u64_t epoch_call_task_count; 124 125 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, epoch_call_tasks, CTLFLAG_RW, 126 &epoch_call_task_count, "# of times a callback task was run"); 127 128 TAILQ_HEAD (threadlist, thread); 129 130 CK_STACK_CONTAINER(struct ck_epoch_entry, stack_entry, 131 ck_epoch_entry_container) 132 133 static struct epoch epoch_array[MAX_EPOCHS]; 134 135 DPCPU_DEFINE(struct grouptask, epoch_cb_task); 136 DPCPU_DEFINE(int, epoch_cb_count); 137 138 static __read_mostly int inited; 139 __read_mostly epoch_t global_epoch; 140 __read_mostly epoch_t global_epoch_preempt; 141 142 static void epoch_call_task(void *context __unused); 143 static uma_zone_t pcpu_zone_record; 144 145 static struct sx epoch_sx; 146 147 #define EPOCH_LOCK() sx_xlock(&epoch_sx) 148 #define EPOCH_UNLOCK() sx_xunlock(&epoch_sx) 149 150 static epoch_record_t 151 epoch_currecord(epoch_t epoch) 152 { 153 154 return (zpcpu_get(epoch->e_pcpu_record)); 155 } 156 157 #ifdef EPOCH_TRACE 158 struct stackentry { 159 RB_ENTRY(stackentry) se_node; 160 struct stack se_stack; 161 }; 162 163 static int 164 stackentry_compare(struct stackentry *a, struct stackentry *b) 165 { 166 167 if (a->se_stack.depth > b->se_stack.depth) 168 return (1); 169 if (a->se_stack.depth < b->se_stack.depth) 170 return (-1); 171 for (int i = 0; i < a->se_stack.depth; i++) { 172 if (a->se_stack.pcs[i] > b->se_stack.pcs[i]) 173 return (1); 174 if (a->se_stack.pcs[i] < b->se_stack.pcs[i]) 175 return (-1); 176 } 177 178 return (0); 179 } 180 181 RB_HEAD(stacktree, stackentry) epoch_stacks = RB_INITIALIZER(&epoch_stacks); 182 RB_GENERATE_STATIC(stacktree, stackentry, se_node, stackentry_compare); 183 184 static struct mtx epoch_stacks_lock; 185 MTX_SYSINIT(epochstacks, &epoch_stacks_lock, "epoch_stacks", MTX_DEF); 186 187 static bool epoch_trace_stack_print = true; 188 SYSCTL_BOOL(_kern_epoch, OID_AUTO, trace_stack_print, CTLFLAG_RWTUN, 189 &epoch_trace_stack_print, 0, "Print stack traces on epoch reports"); 190 191 static void epoch_trace_report(const char *fmt, ...) __printflike(1, 2); 192 static inline void 193 epoch_trace_report(const char *fmt, ...) 194 { 195 va_list ap; 196 struct stackentry se, *new; 197 198 stack_save(&se.se_stack); 199 200 /* Tree is never reduced - go lockless. */ 201 if (RB_FIND(stacktree, &epoch_stacks, &se) != NULL) 202 return; 203 204 new = malloc(sizeof(*new), M_STACK, M_NOWAIT); 205 if (new != NULL) { 206 bcopy(&se.se_stack, &new->se_stack, sizeof(struct stack)); 207 208 mtx_lock(&epoch_stacks_lock); 209 new = RB_INSERT(stacktree, &epoch_stacks, new); 210 mtx_unlock(&epoch_stacks_lock); 211 if (new != NULL) 212 free(new, M_STACK); 213 } 214 215 va_start(ap, fmt); 216 (void)vprintf(fmt, ap); 217 va_end(ap); 218 if (epoch_trace_stack_print) 219 stack_print_ddb(&se.se_stack); 220 } 221 222 static inline void 223 epoch_trace_enter(struct thread *td, epoch_t epoch, epoch_tracker_t et, 224 const char *file, int line) 225 { 226 epoch_tracker_t iet; 227 228 SLIST_FOREACH(iet, &td->td_epochs, et_tlink) { 229 if (iet->et_epoch != epoch) 230 continue; 231 epoch_trace_report("Recursively entering epoch %s " 232 "at %s:%d, previously entered at %s:%d\n", 233 epoch->e_name, file, line, 234 iet->et_file, iet->et_line); 235 } 236 et->et_epoch = epoch; 237 et->et_file = file; 238 et->et_line = line; 239 et->et_flags = 0; 240 SLIST_INSERT_HEAD(&td->td_epochs, et, et_tlink); 241 } 242 243 static inline void 244 epoch_trace_exit(struct thread *td, epoch_t epoch, epoch_tracker_t et, 245 const char *file, int line) 246 { 247 248 if (SLIST_FIRST(&td->td_epochs) != et) { 249 epoch_trace_report("Exiting epoch %s in a not nested order " 250 "at %s:%d. Most recently entered %s at %s:%d\n", 251 epoch->e_name, 252 file, line, 253 SLIST_FIRST(&td->td_epochs)->et_epoch->e_name, 254 SLIST_FIRST(&td->td_epochs)->et_file, 255 SLIST_FIRST(&td->td_epochs)->et_line); 256 /* This will panic if et is not anywhere on td_epochs. */ 257 SLIST_REMOVE(&td->td_epochs, et, epoch_tracker, et_tlink); 258 } else 259 SLIST_REMOVE_HEAD(&td->td_epochs, et_tlink); 260 if (et->et_flags & ET_REPORT_EXIT) 261 printf("Td %p exiting epoch %s at %s:%d\n", td, epoch->e_name, 262 file, line); 263 } 264 265 /* Used by assertions that check thread state before going to sleep. */ 266 void 267 epoch_trace_list(struct thread *td) 268 { 269 epoch_tracker_t iet; 270 271 SLIST_FOREACH(iet, &td->td_epochs, et_tlink) 272 printf("Epoch %s entered at %s:%d\n", iet->et_epoch->e_name, 273 iet->et_file, iet->et_line); 274 } 275 276 void 277 epoch_where_report(epoch_t epoch) 278 { 279 epoch_record_t er; 280 struct epoch_tracker *tdwait; 281 282 MPASS(epoch != NULL); 283 MPASS((epoch->e_flags & EPOCH_PREEMPT) != 0); 284 MPASS(!THREAD_CAN_SLEEP()); 285 critical_enter(); 286 er = epoch_currecord(epoch); 287 TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link) 288 if (tdwait->et_td == curthread) 289 break; 290 critical_exit(); 291 if (tdwait != NULL) { 292 tdwait->et_flags |= ET_REPORT_EXIT; 293 printf("Td %p entered epoch %s at %s:%d\n", curthread, 294 epoch->e_name, tdwait->et_file, tdwait->et_line); 295 } 296 } 297 #endif /* EPOCH_TRACE */ 298 299 static void 300 epoch_init(void *arg __unused) 301 { 302 int cpu; 303 304 block_count = counter_u64_alloc(M_WAITOK); 305 migrate_count = counter_u64_alloc(M_WAITOK); 306 turnstile_count = counter_u64_alloc(M_WAITOK); 307 switch_count = counter_u64_alloc(M_WAITOK); 308 epoch_call_count = counter_u64_alloc(M_WAITOK); 309 epoch_call_task_count = counter_u64_alloc(M_WAITOK); 310 311 pcpu_zone_record = uma_zcreate("epoch_record pcpu", 312 sizeof(struct epoch_record), NULL, NULL, NULL, NULL, 313 UMA_ALIGN_PTR, UMA_ZONE_PCPU); 314 CPU_FOREACH(cpu) { 315 GROUPTASK_INIT(DPCPU_ID_PTR(cpu, epoch_cb_task), 0, 316 epoch_call_task, NULL); 317 taskqgroup_attach_cpu(qgroup_softirq, 318 DPCPU_ID_PTR(cpu, epoch_cb_task), NULL, cpu, NULL, NULL, 319 "epoch call task"); 320 } 321 #ifdef EPOCH_TRACE 322 SLIST_INIT(&thread0.td_epochs); 323 #endif 324 sx_init(&epoch_sx, "epoch-sx"); 325 inited = 1; 326 global_epoch = epoch_alloc("Global", 0); 327 global_epoch_preempt = epoch_alloc("Global preemptible", EPOCH_PREEMPT); 328 } 329 SYSINIT(epoch, SI_SUB_EPOCH, SI_ORDER_FIRST, epoch_init, NULL); 330 331 #if !defined(EARLY_AP_STARTUP) 332 static void 333 epoch_init_smp(void *dummy __unused) 334 { 335 inited = 2; 336 } 337 SYSINIT(epoch_smp, SI_SUB_SMP + 1, SI_ORDER_FIRST, epoch_init_smp, NULL); 338 #endif 339 340 static void 341 epoch_ctor(epoch_t epoch) 342 { 343 epoch_record_t er; 344 int cpu; 345 346 epoch->e_pcpu_record = uma_zalloc_pcpu(pcpu_zone_record, M_WAITOK); 347 CPU_FOREACH(cpu) { 348 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu); 349 bzero(er, sizeof(*er)); 350 ck_epoch_register(&epoch->e_epoch, &er->er_record, NULL); 351 TAILQ_INIT((struct threadlist *)(uintptr_t)&er->er_tdlist); 352 er->er_cpuid = cpu; 353 er->er_parent = epoch; 354 } 355 } 356 357 static void 358 epoch_adjust_prio(struct thread *td, u_char prio) 359 { 360 361 thread_lock(td); 362 sched_prio(td, prio); 363 thread_unlock(td); 364 } 365 366 epoch_t 367 epoch_alloc(const char *name, int flags) 368 { 369 epoch_t epoch; 370 int i; 371 372 MPASS(name != NULL); 373 374 if (__predict_false(!inited)) 375 panic("%s called too early in boot", __func__); 376 377 EPOCH_LOCK(); 378 379 /* 380 * Find a free index in the epoch array. If no free index is 381 * found, try to use the index after the last one. 382 */ 383 for (i = 0;; i++) { 384 /* 385 * If too many epochs are currently allocated, 386 * return NULL. 387 */ 388 if (i == MAX_EPOCHS) { 389 epoch = NULL; 390 goto done; 391 } 392 if (epoch_array[i].e_in_use == 0) 393 break; 394 } 395 396 epoch = epoch_array + i; 397 ck_epoch_init(&epoch->e_epoch); 398 epoch_ctor(epoch); 399 epoch->e_flags = flags; 400 epoch->e_name = name; 401 sx_init(&epoch->e_drain_sx, "epoch-drain-sx"); 402 mtx_init(&epoch->e_drain_mtx, "epoch-drain-mtx", NULL, MTX_DEF); 403 404 /* 405 * Set e_in_use last, because when this field is set the 406 * epoch_call_task() function will start scanning this epoch 407 * structure. 408 */ 409 atomic_store_rel_int(&epoch->e_in_use, 1); 410 done: 411 EPOCH_UNLOCK(); 412 return (epoch); 413 } 414 415 void 416 epoch_free(epoch_t epoch) 417 { 418 #ifdef INVARIANTS 419 int cpu; 420 #endif 421 422 EPOCH_LOCK(); 423 424 MPASS(epoch->e_in_use != 0); 425 426 epoch_drain_callbacks(epoch); 427 428 atomic_store_rel_int(&epoch->e_in_use, 0); 429 /* 430 * Make sure the epoch_call_task() function see e_in_use equal 431 * to zero, by calling epoch_wait() on the global_epoch: 432 */ 433 epoch_wait(global_epoch); 434 #ifdef INVARIANTS 435 CPU_FOREACH(cpu) { 436 epoch_record_t er; 437 438 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu); 439 440 /* 441 * Sanity check: none of the records should be in use anymore. 442 * We drained callbacks above and freeing the pcpu records is 443 * imminent. 444 */ 445 MPASS(er->er_td == NULL); 446 MPASS(TAILQ_EMPTY(&er->er_tdlist)); 447 } 448 #endif 449 uma_zfree_pcpu(pcpu_zone_record, epoch->e_pcpu_record); 450 mtx_destroy(&epoch->e_drain_mtx); 451 sx_destroy(&epoch->e_drain_sx); 452 memset(epoch, 0, sizeof(*epoch)); 453 454 EPOCH_UNLOCK(); 455 } 456 457 #define INIT_CHECK(epoch) \ 458 do { \ 459 if (__predict_false((epoch) == NULL)) \ 460 return; \ 461 } while (0) 462 463 void 464 _epoch_enter_preempt(epoch_t epoch, epoch_tracker_t et EPOCH_FILE_LINE) 465 { 466 struct epoch_record *er; 467 struct thread *td; 468 469 MPASS(cold || epoch != NULL); 470 td = curthread; 471 MPASS(kstack_contains(td, (vm_offset_t)et, sizeof(*et))); 472 473 INIT_CHECK(epoch); 474 MPASS(epoch->e_flags & EPOCH_PREEMPT); 475 476 #ifdef EPOCH_TRACE 477 epoch_trace_enter(td, epoch, et, file, line); 478 #endif 479 et->et_td = td; 480 THREAD_NO_SLEEPING(); 481 critical_enter(); 482 sched_pin(); 483 et->et_old_priority = td->td_priority; 484 er = epoch_currecord(epoch); 485 /* Record-level tracking is reserved for non-preemptible epochs. */ 486 MPASS(er->er_td == NULL); 487 TAILQ_INSERT_TAIL(&er->er_tdlist, et, et_link); 488 ck_epoch_begin(&er->er_record, &et->et_section); 489 critical_exit(); 490 } 491 492 void 493 epoch_enter(epoch_t epoch) 494 { 495 epoch_record_t er; 496 497 MPASS(cold || epoch != NULL); 498 INIT_CHECK(epoch); 499 critical_enter(); 500 er = epoch_currecord(epoch); 501 #ifdef INVARIANTS 502 if (er->er_record.active == 0) { 503 MPASS(er->er_td == NULL); 504 er->er_td = curthread; 505 } else { 506 /* We've recursed, just make sure our accounting isn't wrong. */ 507 MPASS(er->er_td == curthread); 508 } 509 #endif 510 ck_epoch_begin(&er->er_record, NULL); 511 } 512 513 void 514 _epoch_exit_preempt(epoch_t epoch, epoch_tracker_t et EPOCH_FILE_LINE) 515 { 516 struct epoch_record *er; 517 struct thread *td; 518 519 INIT_CHECK(epoch); 520 td = curthread; 521 critical_enter(); 522 sched_unpin(); 523 THREAD_SLEEPING_OK(); 524 er = epoch_currecord(epoch); 525 MPASS(epoch->e_flags & EPOCH_PREEMPT); 526 MPASS(et != NULL); 527 MPASS(et->et_td == td); 528 #ifdef INVARIANTS 529 et->et_td = (void*)0xDEADBEEF; 530 /* Record-level tracking is reserved for non-preemptible epochs. */ 531 MPASS(er->er_td == NULL); 532 #endif 533 ck_epoch_end(&er->er_record, &et->et_section); 534 TAILQ_REMOVE(&er->er_tdlist, et, et_link); 535 er->er_gen++; 536 if (__predict_false(et->et_old_priority != td->td_priority)) 537 epoch_adjust_prio(td, et->et_old_priority); 538 critical_exit(); 539 #ifdef EPOCH_TRACE 540 epoch_trace_exit(td, epoch, et, file, line); 541 #endif 542 } 543 544 void 545 epoch_exit(epoch_t epoch) 546 { 547 epoch_record_t er; 548 549 INIT_CHECK(epoch); 550 er = epoch_currecord(epoch); 551 ck_epoch_end(&er->er_record, NULL); 552 #ifdef INVARIANTS 553 MPASS(er->er_td == curthread); 554 if (er->er_record.active == 0) 555 er->er_td = NULL; 556 #endif 557 critical_exit(); 558 } 559 560 /* 561 * epoch_block_handler_preempt() is a callback from the CK code when another 562 * thread is currently in an epoch section. 563 */ 564 static void 565 epoch_block_handler_preempt(struct ck_epoch *global __unused, 566 ck_epoch_record_t *cr, void *arg __unused) 567 { 568 epoch_record_t record; 569 struct thread *td, *owner, *curwaittd; 570 struct epoch_tracker *tdwait; 571 struct turnstile *ts; 572 struct lock_object *lock; 573 int spincount, gen; 574 int locksheld __unused; 575 576 record = __containerof(cr, struct epoch_record, er_record); 577 td = curthread; 578 locksheld = td->td_locks; 579 spincount = 0; 580 counter_u64_add(block_count, 1); 581 /* 582 * We lost a race and there's no longer any threads 583 * on the CPU in an epoch section. 584 */ 585 if (TAILQ_EMPTY(&record->er_tdlist)) 586 return; 587 588 if (record->er_cpuid != curcpu) { 589 /* 590 * If the head of the list is running, we can wait for it 591 * to remove itself from the list and thus save us the 592 * overhead of a migration 593 */ 594 gen = record->er_gen; 595 thread_unlock(td); 596 /* 597 * We can't actually check if the waiting thread is running 598 * so we simply poll for it to exit before giving up and 599 * migrating. 600 */ 601 do { 602 cpu_spinwait(); 603 } while (!TAILQ_EMPTY(&record->er_tdlist) && 604 gen == record->er_gen && 605 spincount++ < MAX_ADAPTIVE_SPIN); 606 thread_lock(td); 607 /* 608 * If the generation has changed we can poll again 609 * otherwise we need to migrate. 610 */ 611 if (gen != record->er_gen) 612 return; 613 /* 614 * Being on the same CPU as that of the record on which 615 * we need to wait allows us access to the thread 616 * list associated with that CPU. We can then examine the 617 * oldest thread in the queue and wait on its turnstile 618 * until it resumes and so on until a grace period 619 * elapses. 620 * 621 */ 622 counter_u64_add(migrate_count, 1); 623 sched_bind(td, record->er_cpuid); 624 /* 625 * At this point we need to return to the ck code 626 * to scan to see if a grace period has elapsed. 627 * We can't move on to check the thread list, because 628 * in the meantime new threads may have arrived that 629 * in fact belong to a different epoch. 630 */ 631 return; 632 } 633 /* 634 * Try to find a thread in an epoch section on this CPU 635 * waiting on a turnstile. Otherwise find the lowest 636 * priority thread (highest prio value) and drop our priority 637 * to match to allow it to run. 638 */ 639 TAILQ_FOREACH(tdwait, &record->er_tdlist, et_link) { 640 /* 641 * Propagate our priority to any other waiters to prevent us 642 * from starving them. They will have their original priority 643 * restore on exit from epoch_wait(). 644 */ 645 curwaittd = tdwait->et_td; 646 if (!TD_IS_INHIBITED(curwaittd) && curwaittd->td_priority > td->td_priority) { 647 critical_enter(); 648 thread_unlock(td); 649 thread_lock(curwaittd); 650 sched_prio(curwaittd, td->td_priority); 651 thread_unlock(curwaittd); 652 thread_lock(td); 653 critical_exit(); 654 } 655 if (TD_IS_INHIBITED(curwaittd) && TD_ON_LOCK(curwaittd) && 656 ((ts = curwaittd->td_blocked) != NULL)) { 657 /* 658 * We unlock td to allow turnstile_wait to reacquire 659 * the thread lock. Before unlocking it we enter a 660 * critical section to prevent preemption after we 661 * reenable interrupts by dropping the thread lock in 662 * order to prevent curwaittd from getting to run. 663 */ 664 critical_enter(); 665 thread_unlock(td); 666 667 if (turnstile_lock(ts, &lock, &owner)) { 668 if (ts == curwaittd->td_blocked) { 669 MPASS(TD_IS_INHIBITED(curwaittd) && 670 TD_ON_LOCK(curwaittd)); 671 critical_exit(); 672 turnstile_wait(ts, owner, 673 curwaittd->td_tsqueue); 674 counter_u64_add(turnstile_count, 1); 675 thread_lock(td); 676 return; 677 } 678 turnstile_unlock(ts, lock); 679 } 680 thread_lock(td); 681 critical_exit(); 682 KASSERT(td->td_locks == locksheld, 683 ("%d extra locks held", td->td_locks - locksheld)); 684 } 685 } 686 /* 687 * We didn't find any threads actually blocked on a lock 688 * so we have nothing to do except context switch away. 689 */ 690 counter_u64_add(switch_count, 1); 691 mi_switch(SW_VOL | SWT_RELINQUISH); 692 /* 693 * It is important the thread lock is dropped while yielding 694 * to allow other threads to acquire the lock pointed to by 695 * TDQ_LOCKPTR(td). Currently mi_switch() will unlock the 696 * thread lock before returning. Else a deadlock like 697 * situation might happen. 698 */ 699 thread_lock(td); 700 } 701 702 void 703 epoch_wait_preempt(epoch_t epoch) 704 { 705 struct thread *td; 706 int was_bound; 707 int old_cpu; 708 int old_pinned; 709 u_char old_prio; 710 int locks __unused; 711 712 MPASS(cold || epoch != NULL); 713 INIT_CHECK(epoch); 714 td = curthread; 715 #ifdef INVARIANTS 716 locks = curthread->td_locks; 717 MPASS(epoch->e_flags & EPOCH_PREEMPT); 718 if ((epoch->e_flags & EPOCH_LOCKED) == 0) 719 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, 720 "epoch_wait() can be long running"); 721 KASSERT(!in_epoch(epoch), ("epoch_wait_preempt() called in the middle " 722 "of an epoch section of the same epoch")); 723 #endif 724 DROP_GIANT(); 725 thread_lock(td); 726 727 old_cpu = PCPU_GET(cpuid); 728 old_pinned = td->td_pinned; 729 old_prio = td->td_priority; 730 was_bound = sched_is_bound(td); 731 sched_unbind(td); 732 td->td_pinned = 0; 733 sched_bind(td, old_cpu); 734 735 ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler_preempt, 736 NULL); 737 738 /* restore CPU binding, if any */ 739 if (was_bound != 0) { 740 sched_bind(td, old_cpu); 741 } else { 742 /* get thread back to initial CPU, if any */ 743 if (old_pinned != 0) 744 sched_bind(td, old_cpu); 745 sched_unbind(td); 746 } 747 /* restore pinned after bind */ 748 td->td_pinned = old_pinned; 749 750 /* restore thread priority */ 751 sched_prio(td, old_prio); 752 thread_unlock(td); 753 PICKUP_GIANT(); 754 KASSERT(td->td_locks == locks, 755 ("%d residual locks held", td->td_locks - locks)); 756 } 757 758 static void 759 epoch_block_handler(struct ck_epoch *g __unused, ck_epoch_record_t *c __unused, 760 void *arg __unused) 761 { 762 cpu_spinwait(); 763 } 764 765 void 766 epoch_wait(epoch_t epoch) 767 { 768 769 MPASS(cold || epoch != NULL); 770 INIT_CHECK(epoch); 771 MPASS(epoch->e_flags == 0); 772 critical_enter(); 773 ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler, NULL); 774 critical_exit(); 775 } 776 777 void 778 epoch_call(epoch_t epoch, epoch_callback_t callback, epoch_context_t ctx) 779 { 780 epoch_record_t er; 781 ck_epoch_entry_t *cb; 782 783 cb = (void *)ctx; 784 785 MPASS(callback); 786 /* too early in boot to have epoch set up */ 787 if (__predict_false(epoch == NULL)) 788 goto boottime; 789 #if !defined(EARLY_AP_STARTUP) 790 if (__predict_false(inited < 2)) 791 goto boottime; 792 #endif 793 794 critical_enter(); 795 *DPCPU_PTR(epoch_cb_count) += 1; 796 er = epoch_currecord(epoch); 797 ck_epoch_call(&er->er_record, cb, (ck_epoch_cb_t *)callback); 798 critical_exit(); 799 return; 800 boottime: 801 callback(ctx); 802 } 803 804 static void 805 epoch_call_task(void *arg __unused) 806 { 807 ck_stack_entry_t *cursor, *head, *next; 808 ck_epoch_record_t *record; 809 epoch_record_t er; 810 epoch_t epoch; 811 ck_stack_t cb_stack; 812 int i, npending, total; 813 814 ck_stack_init(&cb_stack); 815 critical_enter(); 816 epoch_enter(global_epoch); 817 for (total = i = 0; i != MAX_EPOCHS; i++) { 818 epoch = epoch_array + i; 819 if (__predict_false( 820 atomic_load_acq_int(&epoch->e_in_use) == 0)) 821 continue; 822 er = epoch_currecord(epoch); 823 record = &er->er_record; 824 if ((npending = record->n_pending) == 0) 825 continue; 826 ck_epoch_poll_deferred(record, &cb_stack); 827 total += npending - record->n_pending; 828 } 829 epoch_exit(global_epoch); 830 *DPCPU_PTR(epoch_cb_count) -= total; 831 critical_exit(); 832 833 counter_u64_add(epoch_call_count, total); 834 counter_u64_add(epoch_call_task_count, 1); 835 836 head = ck_stack_batch_pop_npsc(&cb_stack); 837 for (cursor = head; cursor != NULL; cursor = next) { 838 struct ck_epoch_entry *entry = 839 ck_epoch_entry_container(cursor); 840 841 next = CK_STACK_NEXT(cursor); 842 entry->function(entry); 843 } 844 } 845 846 static int 847 in_epoch_verbose_preempt(epoch_t epoch, int dump_onfail) 848 { 849 epoch_record_t er; 850 struct epoch_tracker *tdwait; 851 struct thread *td; 852 853 MPASS(epoch != NULL); 854 MPASS((epoch->e_flags & EPOCH_PREEMPT) != 0); 855 td = curthread; 856 if (THREAD_CAN_SLEEP()) 857 return (0); 858 critical_enter(); 859 er = epoch_currecord(epoch); 860 TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link) 861 if (tdwait->et_td == td) { 862 critical_exit(); 863 return (1); 864 } 865 #ifdef INVARIANTS 866 if (dump_onfail) { 867 MPASS(td->td_pinned); 868 printf("cpu: %d id: %d\n", curcpu, td->td_tid); 869 TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link) 870 printf("td_tid: %d ", tdwait->et_td->td_tid); 871 printf("\n"); 872 } 873 #endif 874 critical_exit(); 875 return (0); 876 } 877 878 #ifdef INVARIANTS 879 static void 880 epoch_assert_nocpu(epoch_t epoch, struct thread *td) 881 { 882 epoch_record_t er; 883 int cpu; 884 bool crit; 885 886 crit = td->td_critnest > 0; 887 888 /* Check for a critical section mishap. */ 889 CPU_FOREACH(cpu) { 890 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu); 891 KASSERT(er->er_td != td, 892 ("%s critical section in epoch '%s', from cpu %d", 893 (crit ? "exited" : "re-entered"), epoch->e_name, cpu)); 894 } 895 } 896 #else 897 #define epoch_assert_nocpu(e, td) do {} while (0) 898 #endif 899 900 int 901 in_epoch_verbose(epoch_t epoch, int dump_onfail) 902 { 903 epoch_record_t er; 904 struct thread *td; 905 906 if (__predict_false((epoch) == NULL)) 907 return (0); 908 if ((epoch->e_flags & EPOCH_PREEMPT) != 0) 909 return (in_epoch_verbose_preempt(epoch, dump_onfail)); 910 911 /* 912 * The thread being in a critical section is a necessary 913 * condition to be correctly inside a non-preemptible epoch, 914 * so it's definitely not in this epoch. 915 */ 916 td = curthread; 917 if (td->td_critnest == 0) { 918 epoch_assert_nocpu(epoch, td); 919 return (0); 920 } 921 922 /* 923 * The current cpu is in a critical section, so the epoch record will be 924 * stable for the rest of this function. Knowing that the record is not 925 * active is sufficient for knowing whether we're in this epoch or not, 926 * since it's a pcpu record. 927 */ 928 er = epoch_currecord(epoch); 929 if (er->er_record.active == 0) { 930 epoch_assert_nocpu(epoch, td); 931 return (0); 932 } 933 934 MPASS(er->er_td == td); 935 return (1); 936 } 937 938 int 939 in_epoch(epoch_t epoch) 940 { 941 return (in_epoch_verbose(epoch, 0)); 942 } 943 944 static void 945 epoch_drain_cb(struct epoch_context *ctx) 946 { 947 struct epoch *epoch = 948 __containerof(ctx, struct epoch_record, er_drain_ctx)->er_parent; 949 950 if (atomic_fetchadd_int(&epoch->e_drain_count, -1) == 1) { 951 mtx_lock(&epoch->e_drain_mtx); 952 wakeup(epoch); 953 mtx_unlock(&epoch->e_drain_mtx); 954 } 955 } 956 957 void 958 epoch_drain_callbacks(epoch_t epoch) 959 { 960 epoch_record_t er; 961 struct thread *td; 962 int was_bound; 963 int old_pinned; 964 int old_cpu; 965 int cpu; 966 967 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, 968 "epoch_drain_callbacks() may sleep!"); 969 970 /* too early in boot to have epoch set up */ 971 if (__predict_false(epoch == NULL)) 972 return; 973 #if !defined(EARLY_AP_STARTUP) 974 if (__predict_false(inited < 2)) 975 return; 976 #endif 977 DROP_GIANT(); 978 979 sx_xlock(&epoch->e_drain_sx); 980 mtx_lock(&epoch->e_drain_mtx); 981 982 td = curthread; 983 thread_lock(td); 984 old_cpu = PCPU_GET(cpuid); 985 old_pinned = td->td_pinned; 986 was_bound = sched_is_bound(td); 987 sched_unbind(td); 988 td->td_pinned = 0; 989 990 CPU_FOREACH(cpu) 991 epoch->e_drain_count++; 992 CPU_FOREACH(cpu) { 993 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu); 994 sched_bind(td, cpu); 995 epoch_call(epoch, &epoch_drain_cb, &er->er_drain_ctx); 996 } 997 998 /* restore CPU binding, if any */ 999 if (was_bound != 0) { 1000 sched_bind(td, old_cpu); 1001 } else { 1002 /* get thread back to initial CPU, if any */ 1003 if (old_pinned != 0) 1004 sched_bind(td, old_cpu); 1005 sched_unbind(td); 1006 } 1007 /* restore pinned after bind */ 1008 td->td_pinned = old_pinned; 1009 1010 thread_unlock(td); 1011 1012 while (epoch->e_drain_count != 0) 1013 msleep(epoch, &epoch->e_drain_mtx, PZERO, "EDRAIN", 0); 1014 1015 mtx_unlock(&epoch->e_drain_mtx); 1016 sx_xunlock(&epoch->e_drain_sx); 1017 1018 PICKUP_GIANT(); 1019 }
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