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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 #ifdef EPOCH_TRACE 151 struct stackentry { 152 RB_ENTRY(stackentry) se_node; 153 struct stack se_stack; 154 }; 155 156 static int 157 stackentry_compare(struct stackentry *a, struct stackentry *b) 158 { 159 160 if (a->se_stack.depth > b->se_stack.depth) 161 return (1); 162 if (a->se_stack.depth < b->se_stack.depth) 163 return (-1); 164 for (int i = 0; i < a->se_stack.depth; i++) { 165 if (a->se_stack.pcs[i] > b->se_stack.pcs[i]) 166 return (1); 167 if (a->se_stack.pcs[i] < b->se_stack.pcs[i]) 168 return (-1); 169 } 170 171 return (0); 172 } 173 174 RB_HEAD(stacktree, stackentry) epoch_stacks = RB_INITIALIZER(&epoch_stacks); 175 RB_GENERATE_STATIC(stacktree, stackentry, se_node, stackentry_compare); 176 177 static struct mtx epoch_stacks_lock; 178 MTX_SYSINIT(epochstacks, &epoch_stacks_lock, "epoch_stacks", MTX_DEF); 179 180 static bool epoch_trace_stack_print = true; 181 SYSCTL_BOOL(_kern_epoch, OID_AUTO, trace_stack_print, CTLFLAG_RWTUN, 182 &epoch_trace_stack_print, 0, "Print stack traces on epoch reports"); 183 184 static void epoch_trace_report(const char *fmt, ...) __printflike(1, 2); 185 static inline void 186 epoch_trace_report(const char *fmt, ...) 187 { 188 va_list ap; 189 struct stackentry se, *new; 190 191 stack_zero(&se.se_stack); /* XXX: is it really needed? */ 192 stack_save(&se.se_stack); 193 194 /* Tree is never reduced - go lockless. */ 195 if (RB_FIND(stacktree, &epoch_stacks, &se) != NULL) 196 return; 197 198 new = malloc(sizeof(*new), M_STACK, M_NOWAIT); 199 if (new != NULL) { 200 bcopy(&se.se_stack, &new->se_stack, sizeof(struct stack)); 201 202 mtx_lock(&epoch_stacks_lock); 203 new = RB_INSERT(stacktree, &epoch_stacks, new); 204 mtx_unlock(&epoch_stacks_lock); 205 if (new != NULL) 206 free(new, M_STACK); 207 } 208 209 va_start(ap, fmt); 210 (void)vprintf(fmt, ap); 211 va_end(ap); 212 if (epoch_trace_stack_print) 213 stack_print_ddb(&se.se_stack); 214 } 215 216 static inline void 217 epoch_trace_enter(struct thread *td, epoch_t epoch, epoch_tracker_t et, 218 const char *file, int line) 219 { 220 epoch_tracker_t iet; 221 222 SLIST_FOREACH(iet, &td->td_epochs, et_tlink) 223 if (iet->et_epoch == epoch) 224 epoch_trace_report("Recursively entering epoch %s " 225 "at %s:%d, previously entered at %s:%d\n", 226 epoch->e_name, file, line, 227 iet->et_file, iet->et_line); 228 et->et_epoch = epoch; 229 et->et_file = file; 230 et->et_line = line; 231 SLIST_INSERT_HEAD(&td->td_epochs, et, et_tlink); 232 } 233 234 static inline void 235 epoch_trace_exit(struct thread *td, epoch_t epoch, epoch_tracker_t et, 236 const char *file, int line) 237 { 238 239 if (SLIST_FIRST(&td->td_epochs) != et) { 240 epoch_trace_report("Exiting epoch %s in a not nested order " 241 "at %s:%d. Most recently entered %s at %s:%d\n", 242 epoch->e_name, 243 file, line, 244 SLIST_FIRST(&td->td_epochs)->et_epoch->e_name, 245 SLIST_FIRST(&td->td_epochs)->et_file, 246 SLIST_FIRST(&td->td_epochs)->et_line); 247 /* This will panic if et is not anywhere on td_epochs. */ 248 SLIST_REMOVE(&td->td_epochs, et, epoch_tracker, et_tlink); 249 } else 250 SLIST_REMOVE_HEAD(&td->td_epochs, et_tlink); 251 } 252 253 /* Used by assertions that check thread state before going to sleep. */ 254 void 255 epoch_trace_list(struct thread *td) 256 { 257 epoch_tracker_t iet; 258 259 SLIST_FOREACH(iet, &td->td_epochs, et_tlink) 260 printf("Epoch %s entered at %s:%d\n", iet->et_epoch->e_name, 261 iet->et_file, iet->et_line); 262 } 263 #endif /* EPOCH_TRACE */ 264 265 static void 266 epoch_init(void *arg __unused) 267 { 268 int cpu; 269 270 block_count = counter_u64_alloc(M_WAITOK); 271 migrate_count = counter_u64_alloc(M_WAITOK); 272 turnstile_count = counter_u64_alloc(M_WAITOK); 273 switch_count = counter_u64_alloc(M_WAITOK); 274 epoch_call_count = counter_u64_alloc(M_WAITOK); 275 epoch_call_task_count = counter_u64_alloc(M_WAITOK); 276 277 pcpu_zone_record = uma_zcreate("epoch_record pcpu", 278 sizeof(struct epoch_record), NULL, NULL, NULL, NULL, 279 UMA_ALIGN_PTR, UMA_ZONE_PCPU); 280 CPU_FOREACH(cpu) { 281 GROUPTASK_INIT(DPCPU_ID_PTR(cpu, epoch_cb_task), 0, 282 epoch_call_task, NULL); 283 taskqgroup_attach_cpu(qgroup_softirq, 284 DPCPU_ID_PTR(cpu, epoch_cb_task), NULL, cpu, NULL, NULL, 285 "epoch call task"); 286 } 287 #ifdef EPOCH_TRACE 288 SLIST_INIT(&thread0.td_epochs); 289 #endif 290 sx_init(&epoch_sx, "epoch-sx"); 291 inited = 1; 292 global_epoch = epoch_alloc("Global", 0); 293 global_epoch_preempt = epoch_alloc("Global preemptible", EPOCH_PREEMPT); 294 } 295 SYSINIT(epoch, SI_SUB_EPOCH, SI_ORDER_FIRST, epoch_init, NULL); 296 297 #if !defined(EARLY_AP_STARTUP) 298 static void 299 epoch_init_smp(void *dummy __unused) 300 { 301 inited = 2; 302 } 303 SYSINIT(epoch_smp, SI_SUB_SMP + 1, SI_ORDER_FIRST, epoch_init_smp, NULL); 304 #endif 305 306 static void 307 epoch_ctor(epoch_t epoch) 308 { 309 epoch_record_t er; 310 int cpu; 311 312 epoch->e_pcpu_record = uma_zalloc_pcpu(pcpu_zone_record, M_WAITOK); 313 CPU_FOREACH(cpu) { 314 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu); 315 bzero(er, sizeof(*er)); 316 ck_epoch_register(&epoch->e_epoch, &er->er_record, NULL); 317 TAILQ_INIT((struct threadlist *)(uintptr_t)&er->er_tdlist); 318 er->er_cpuid = cpu; 319 er->er_parent = epoch; 320 } 321 } 322 323 static void 324 epoch_adjust_prio(struct thread *td, u_char prio) 325 { 326 327 thread_lock(td); 328 sched_prio(td, prio); 329 thread_unlock(td); 330 } 331 332 epoch_t 333 epoch_alloc(const char *name, int flags) 334 { 335 epoch_t epoch; 336 int i; 337 338 MPASS(name != NULL); 339 340 if (__predict_false(!inited)) 341 panic("%s called too early in boot", __func__); 342 343 EPOCH_LOCK(); 344 345 /* 346 * Find a free index in the epoch array. If no free index is 347 * found, try to use the index after the last one. 348 */ 349 for (i = 0;; i++) { 350 /* 351 * If too many epochs are currently allocated, 352 * return NULL. 353 */ 354 if (i == MAX_EPOCHS) { 355 epoch = NULL; 356 goto done; 357 } 358 if (epoch_array[i].e_in_use == 0) 359 break; 360 } 361 362 epoch = epoch_array + i; 363 ck_epoch_init(&epoch->e_epoch); 364 epoch_ctor(epoch); 365 epoch->e_flags = flags; 366 epoch->e_name = name; 367 sx_init(&epoch->e_drain_sx, "epoch-drain-sx"); 368 mtx_init(&epoch->e_drain_mtx, "epoch-drain-mtx", NULL, MTX_DEF); 369 370 /* 371 * Set e_in_use last, because when this field is set the 372 * epoch_call_task() function will start scanning this epoch 373 * structure. 374 */ 375 atomic_store_rel_int(&epoch->e_in_use, 1); 376 done: 377 EPOCH_UNLOCK(); 378 return (epoch); 379 } 380 381 void 382 epoch_free(epoch_t epoch) 383 { 384 #ifdef INVARIANTS 385 int cpu; 386 #endif 387 388 EPOCH_LOCK(); 389 390 MPASS(epoch->e_in_use != 0); 391 392 epoch_drain_callbacks(epoch); 393 394 atomic_store_rel_int(&epoch->e_in_use, 0); 395 /* 396 * Make sure the epoch_call_task() function see e_in_use equal 397 * to zero, by calling epoch_wait() on the global_epoch: 398 */ 399 epoch_wait(global_epoch); 400 #ifdef INVARIANTS 401 CPU_FOREACH(cpu) { 402 epoch_record_t er; 403 404 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu); 405 406 /* 407 * Sanity check: none of the records should be in use anymore. 408 * We drained callbacks above and freeing the pcpu records is 409 * imminent. 410 */ 411 MPASS(er->er_td == NULL); 412 MPASS(TAILQ_EMPTY(&er->er_tdlist)); 413 } 414 #endif 415 uma_zfree_pcpu(pcpu_zone_record, epoch->e_pcpu_record); 416 mtx_destroy(&epoch->e_drain_mtx); 417 sx_destroy(&epoch->e_drain_sx); 418 memset(epoch, 0, sizeof(*epoch)); 419 420 EPOCH_UNLOCK(); 421 } 422 423 static epoch_record_t 424 epoch_currecord(epoch_t epoch) 425 { 426 427 return (zpcpu_get(epoch->e_pcpu_record)); 428 } 429 430 #define INIT_CHECK(epoch) \ 431 do { \ 432 if (__predict_false((epoch) == NULL)) \ 433 return; \ 434 } while (0) 435 436 void 437 _epoch_enter_preempt(epoch_t epoch, epoch_tracker_t et EPOCH_FILE_LINE) 438 { 439 struct epoch_record *er; 440 struct thread *td; 441 442 MPASS(cold || epoch != NULL); 443 MPASS(epoch->e_flags & EPOCH_PREEMPT); 444 td = curthread; 445 MPASS((vm_offset_t)et >= td->td_kstack && 446 (vm_offset_t)et + sizeof(struct epoch_tracker) <= 447 td->td_kstack + td->td_kstack_pages * PAGE_SIZE); 448 449 INIT_CHECK(epoch); 450 #ifdef EPOCH_TRACE 451 epoch_trace_enter(td, epoch, et, file, line); 452 #endif 453 et->et_td = td; 454 THREAD_NO_SLEEPING(); 455 critical_enter(); 456 sched_pin(); 457 td->td_pre_epoch_prio = td->td_priority; 458 er = epoch_currecord(epoch); 459 /* Record-level tracking is reserved for non-preemptible epochs. */ 460 MPASS(er->er_td == NULL); 461 TAILQ_INSERT_TAIL(&er->er_tdlist, et, et_link); 462 ck_epoch_begin(&er->er_record, &et->et_section); 463 critical_exit(); 464 } 465 466 void 467 epoch_enter(epoch_t epoch) 468 { 469 epoch_record_t er; 470 471 MPASS(cold || epoch != NULL); 472 INIT_CHECK(epoch); 473 critical_enter(); 474 er = epoch_currecord(epoch); 475 #ifdef INVARIANTS 476 if (er->er_record.active == 0) { 477 MPASS(er->er_td == NULL); 478 er->er_td = curthread; 479 } else { 480 /* We've recursed, just make sure our accounting isn't wrong. */ 481 MPASS(er->er_td == curthread); 482 } 483 #endif 484 ck_epoch_begin(&er->er_record, NULL); 485 } 486 487 void 488 _epoch_exit_preempt(epoch_t epoch, epoch_tracker_t et EPOCH_FILE_LINE) 489 { 490 struct epoch_record *er; 491 struct thread *td; 492 493 INIT_CHECK(epoch); 494 td = curthread; 495 critical_enter(); 496 sched_unpin(); 497 THREAD_SLEEPING_OK(); 498 er = epoch_currecord(epoch); 499 MPASS(epoch->e_flags & EPOCH_PREEMPT); 500 MPASS(et != NULL); 501 MPASS(et->et_td == td); 502 #ifdef INVARIANTS 503 et->et_td = (void*)0xDEADBEEF; 504 /* Record-level tracking is reserved for non-preemptible epochs. */ 505 MPASS(er->er_td == NULL); 506 #endif 507 ck_epoch_end(&er->er_record, &et->et_section); 508 TAILQ_REMOVE(&er->er_tdlist, et, et_link); 509 er->er_gen++; 510 if (__predict_false(td->td_pre_epoch_prio != td->td_priority)) 511 epoch_adjust_prio(td, td->td_pre_epoch_prio); 512 critical_exit(); 513 #ifdef EPOCH_TRACE 514 epoch_trace_exit(td, epoch, et, file, line); 515 #endif 516 } 517 518 void 519 epoch_exit(epoch_t epoch) 520 { 521 epoch_record_t er; 522 523 INIT_CHECK(epoch); 524 er = epoch_currecord(epoch); 525 ck_epoch_end(&er->er_record, NULL); 526 #ifdef INVARIANTS 527 MPASS(er->er_td == curthread); 528 if (er->er_record.active == 0) 529 er->er_td = NULL; 530 #endif 531 critical_exit(); 532 } 533 534 /* 535 * epoch_block_handler_preempt() is a callback from the CK code when another 536 * thread is currently in an epoch section. 537 */ 538 static void 539 epoch_block_handler_preempt(struct ck_epoch *global __unused, 540 ck_epoch_record_t *cr, void *arg __unused) 541 { 542 epoch_record_t record; 543 struct thread *td, *owner, *curwaittd; 544 struct epoch_tracker *tdwait; 545 struct turnstile *ts; 546 struct lock_object *lock; 547 int spincount, gen; 548 int locksheld __unused; 549 550 record = __containerof(cr, struct epoch_record, er_record); 551 td = curthread; 552 locksheld = td->td_locks; 553 spincount = 0; 554 counter_u64_add(block_count, 1); 555 /* 556 * We lost a race and there's no longer any threads 557 * on the CPU in an epoch section. 558 */ 559 if (TAILQ_EMPTY(&record->er_tdlist)) 560 return; 561 562 if (record->er_cpuid != curcpu) { 563 /* 564 * If the head of the list is running, we can wait for it 565 * to remove itself from the list and thus save us the 566 * overhead of a migration 567 */ 568 gen = record->er_gen; 569 thread_unlock(td); 570 /* 571 * We can't actually check if the waiting thread is running 572 * so we simply poll for it to exit before giving up and 573 * migrating. 574 */ 575 do { 576 cpu_spinwait(); 577 } while (!TAILQ_EMPTY(&record->er_tdlist) && 578 gen == record->er_gen && 579 spincount++ < MAX_ADAPTIVE_SPIN); 580 thread_lock(td); 581 /* 582 * If the generation has changed we can poll again 583 * otherwise we need to migrate. 584 */ 585 if (gen != record->er_gen) 586 return; 587 /* 588 * Being on the same CPU as that of the record on which 589 * we need to wait allows us access to the thread 590 * list associated with that CPU. We can then examine the 591 * oldest thread in the queue and wait on its turnstile 592 * until it resumes and so on until a grace period 593 * elapses. 594 * 595 */ 596 counter_u64_add(migrate_count, 1); 597 sched_bind(td, record->er_cpuid); 598 /* 599 * At this point we need to return to the ck code 600 * to scan to see if a grace period has elapsed. 601 * We can't move on to check the thread list, because 602 * in the meantime new threads may have arrived that 603 * in fact belong to a different epoch. 604 */ 605 return; 606 } 607 /* 608 * Try to find a thread in an epoch section on this CPU 609 * waiting on a turnstile. Otherwise find the lowest 610 * priority thread (highest prio value) and drop our priority 611 * to match to allow it to run. 612 */ 613 TAILQ_FOREACH(tdwait, &record->er_tdlist, et_link) { 614 /* 615 * Propagate our priority to any other waiters to prevent us 616 * from starving them. They will have their original priority 617 * restore on exit from epoch_wait(). 618 */ 619 curwaittd = tdwait->et_td; 620 if (!TD_IS_INHIBITED(curwaittd) && curwaittd->td_priority > td->td_priority) { 621 critical_enter(); 622 thread_unlock(td); 623 thread_lock(curwaittd); 624 sched_prio(curwaittd, td->td_priority); 625 thread_unlock(curwaittd); 626 thread_lock(td); 627 critical_exit(); 628 } 629 if (TD_IS_INHIBITED(curwaittd) && TD_ON_LOCK(curwaittd) && 630 ((ts = curwaittd->td_blocked) != NULL)) { 631 /* 632 * We unlock td to allow turnstile_wait to reacquire 633 * the thread lock. Before unlocking it we enter a 634 * critical section to prevent preemption after we 635 * reenable interrupts by dropping the thread lock in 636 * order to prevent curwaittd from getting to run. 637 */ 638 critical_enter(); 639 thread_unlock(td); 640 641 if (turnstile_lock(ts, &lock, &owner)) { 642 if (ts == curwaittd->td_blocked) { 643 MPASS(TD_IS_INHIBITED(curwaittd) && 644 TD_ON_LOCK(curwaittd)); 645 critical_exit(); 646 turnstile_wait(ts, owner, 647 curwaittd->td_tsqueue); 648 counter_u64_add(turnstile_count, 1); 649 thread_lock(td); 650 return; 651 } 652 turnstile_unlock(ts, lock); 653 } 654 thread_lock(td); 655 critical_exit(); 656 KASSERT(td->td_locks == locksheld, 657 ("%d extra locks held", td->td_locks - locksheld)); 658 } 659 } 660 /* 661 * We didn't find any threads actually blocked on a lock 662 * so we have nothing to do except context switch away. 663 */ 664 counter_u64_add(switch_count, 1); 665 mi_switch(SW_VOL | SWT_RELINQUISH); 666 /* 667 * It is important the thread lock is dropped while yielding 668 * to allow other threads to acquire the lock pointed to by 669 * TDQ_LOCKPTR(td). Currently mi_switch() will unlock the 670 * thread lock before returning. Else a deadlock like 671 * situation might happen. 672 */ 673 thread_lock(td); 674 } 675 676 void 677 epoch_wait_preempt(epoch_t epoch) 678 { 679 struct thread *td; 680 int was_bound; 681 int old_cpu; 682 int old_pinned; 683 u_char old_prio; 684 int locks __unused; 685 686 MPASS(cold || epoch != NULL); 687 INIT_CHECK(epoch); 688 td = curthread; 689 #ifdef INVARIANTS 690 locks = curthread->td_locks; 691 MPASS(epoch->e_flags & EPOCH_PREEMPT); 692 if ((epoch->e_flags & EPOCH_LOCKED) == 0) 693 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, 694 "epoch_wait() can be long running"); 695 KASSERT(!in_epoch(epoch), ("epoch_wait_preempt() called in the middle " 696 "of an epoch section of the same epoch")); 697 #endif 698 DROP_GIANT(); 699 thread_lock(td); 700 701 old_cpu = PCPU_GET(cpuid); 702 old_pinned = td->td_pinned; 703 old_prio = td->td_priority; 704 was_bound = sched_is_bound(td); 705 sched_unbind(td); 706 td->td_pinned = 0; 707 sched_bind(td, old_cpu); 708 709 ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler_preempt, 710 NULL); 711 712 /* restore CPU binding, if any */ 713 if (was_bound != 0) { 714 sched_bind(td, old_cpu); 715 } else { 716 /* get thread back to initial CPU, if any */ 717 if (old_pinned != 0) 718 sched_bind(td, old_cpu); 719 sched_unbind(td); 720 } 721 /* restore pinned after bind */ 722 td->td_pinned = old_pinned; 723 724 /* restore thread priority */ 725 sched_prio(td, old_prio); 726 thread_unlock(td); 727 PICKUP_GIANT(); 728 KASSERT(td->td_locks == locks, 729 ("%d residual locks held", td->td_locks - locks)); 730 } 731 732 static void 733 epoch_block_handler(struct ck_epoch *g __unused, ck_epoch_record_t *c __unused, 734 void *arg __unused) 735 { 736 cpu_spinwait(); 737 } 738 739 void 740 epoch_wait(epoch_t epoch) 741 { 742 743 MPASS(cold || epoch != NULL); 744 INIT_CHECK(epoch); 745 MPASS(epoch->e_flags == 0); 746 critical_enter(); 747 ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler, NULL); 748 critical_exit(); 749 } 750 751 void 752 epoch_call(epoch_t epoch, epoch_callback_t callback, epoch_context_t ctx) 753 { 754 epoch_record_t er; 755 ck_epoch_entry_t *cb; 756 757 cb = (void *)ctx; 758 759 MPASS(callback); 760 /* too early in boot to have epoch set up */ 761 if (__predict_false(epoch == NULL)) 762 goto boottime; 763 #if !defined(EARLY_AP_STARTUP) 764 if (__predict_false(inited < 2)) 765 goto boottime; 766 #endif 767 768 critical_enter(); 769 *DPCPU_PTR(epoch_cb_count) += 1; 770 er = epoch_currecord(epoch); 771 ck_epoch_call(&er->er_record, cb, (ck_epoch_cb_t *)callback); 772 critical_exit(); 773 return; 774 boottime: 775 callback(ctx); 776 } 777 778 static void 779 epoch_call_task(void *arg __unused) 780 { 781 ck_stack_entry_t *cursor, *head, *next; 782 ck_epoch_record_t *record; 783 epoch_record_t er; 784 epoch_t epoch; 785 ck_stack_t cb_stack; 786 int i, npending, total; 787 788 ck_stack_init(&cb_stack); 789 critical_enter(); 790 epoch_enter(global_epoch); 791 for (total = i = 0; i != MAX_EPOCHS; i++) { 792 epoch = epoch_array + i; 793 if (__predict_false( 794 atomic_load_acq_int(&epoch->e_in_use) == 0)) 795 continue; 796 er = epoch_currecord(epoch); 797 record = &er->er_record; 798 if ((npending = record->n_pending) == 0) 799 continue; 800 ck_epoch_poll_deferred(record, &cb_stack); 801 total += npending - record->n_pending; 802 } 803 epoch_exit(global_epoch); 804 *DPCPU_PTR(epoch_cb_count) -= total; 805 critical_exit(); 806 807 counter_u64_add(epoch_call_count, total); 808 counter_u64_add(epoch_call_task_count, 1); 809 810 head = ck_stack_batch_pop_npsc(&cb_stack); 811 for (cursor = head; cursor != NULL; cursor = next) { 812 struct ck_epoch_entry *entry = 813 ck_epoch_entry_container(cursor); 814 815 next = CK_STACK_NEXT(cursor); 816 entry->function(entry); 817 } 818 } 819 820 static int 821 in_epoch_verbose_preempt(epoch_t epoch, int dump_onfail) 822 { 823 epoch_record_t er; 824 struct epoch_tracker *tdwait; 825 struct thread *td; 826 827 MPASS(epoch != NULL); 828 MPASS((epoch->e_flags & EPOCH_PREEMPT) != 0); 829 td = curthread; 830 if (THREAD_CAN_SLEEP()) 831 return (0); 832 critical_enter(); 833 er = epoch_currecord(epoch); 834 TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link) 835 if (tdwait->et_td == td) { 836 critical_exit(); 837 return (1); 838 } 839 #ifdef INVARIANTS 840 if (dump_onfail) { 841 MPASS(td->td_pinned); 842 printf("cpu: %d id: %d\n", curcpu, td->td_tid); 843 TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link) 844 printf("td_tid: %d ", tdwait->et_td->td_tid); 845 printf("\n"); 846 } 847 #endif 848 critical_exit(); 849 return (0); 850 } 851 852 #ifdef INVARIANTS 853 static void 854 epoch_assert_nocpu(epoch_t epoch, struct thread *td) 855 { 856 epoch_record_t er; 857 int cpu; 858 bool crit; 859 860 crit = td->td_critnest > 0; 861 862 /* Check for a critical section mishap. */ 863 CPU_FOREACH(cpu) { 864 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu); 865 KASSERT(er->er_td != td, 866 ("%s critical section in epoch '%s', from cpu %d", 867 (crit ? "exited" : "re-entered"), epoch->e_name, cpu)); 868 } 869 } 870 #else 871 #define epoch_assert_nocpu(e, td) 872 #endif 873 874 int 875 in_epoch_verbose(epoch_t epoch, int dump_onfail) 876 { 877 epoch_record_t er; 878 struct thread *td; 879 880 if (__predict_false((epoch) == NULL)) 881 return (0); 882 if ((epoch->e_flags & EPOCH_PREEMPT) != 0) 883 return (in_epoch_verbose_preempt(epoch, dump_onfail)); 884 885 /* 886 * The thread being in a critical section is a necessary 887 * condition to be correctly inside a non-preemptible epoch, 888 * so it's definitely not in this epoch. 889 */ 890 td = curthread; 891 if (td->td_critnest == 0) { 892 epoch_assert_nocpu(epoch, td); 893 return (0); 894 } 895 896 /* 897 * The current cpu is in a critical section, so the epoch record will be 898 * stable for the rest of this function. Knowing that the record is not 899 * active is sufficient for knowing whether we're in this epoch or not, 900 * since it's a pcpu record. 901 */ 902 er = epoch_currecord(epoch); 903 if (er->er_record.active == 0) { 904 epoch_assert_nocpu(epoch, td); 905 return (0); 906 } 907 908 MPASS(er->er_td == td); 909 return (1); 910 } 911 912 int 913 in_epoch(epoch_t epoch) 914 { 915 return (in_epoch_verbose(epoch, 0)); 916 } 917 918 static void 919 epoch_drain_cb(struct epoch_context *ctx) 920 { 921 struct epoch *epoch = 922 __containerof(ctx, struct epoch_record, er_drain_ctx)->er_parent; 923 924 if (atomic_fetchadd_int(&epoch->e_drain_count, -1) == 1) { 925 mtx_lock(&epoch->e_drain_mtx); 926 wakeup(epoch); 927 mtx_unlock(&epoch->e_drain_mtx); 928 } 929 } 930 931 void 932 epoch_drain_callbacks(epoch_t epoch) 933 { 934 epoch_record_t er; 935 struct thread *td; 936 int was_bound; 937 int old_pinned; 938 int old_cpu; 939 int cpu; 940 941 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, 942 "epoch_drain_callbacks() may sleep!"); 943 944 /* too early in boot to have epoch set up */ 945 if (__predict_false(epoch == NULL)) 946 return; 947 #if !defined(EARLY_AP_STARTUP) 948 if (__predict_false(inited < 2)) 949 return; 950 #endif 951 DROP_GIANT(); 952 953 sx_xlock(&epoch->e_drain_sx); 954 mtx_lock(&epoch->e_drain_mtx); 955 956 td = curthread; 957 thread_lock(td); 958 old_cpu = PCPU_GET(cpuid); 959 old_pinned = td->td_pinned; 960 was_bound = sched_is_bound(td); 961 sched_unbind(td); 962 td->td_pinned = 0; 963 964 CPU_FOREACH(cpu) 965 epoch->e_drain_count++; 966 CPU_FOREACH(cpu) { 967 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu); 968 sched_bind(td, cpu); 969 epoch_call(epoch, &epoch_drain_cb, &er->er_drain_ctx); 970 } 971 972 /* restore CPU binding, if any */ 973 if (was_bound != 0) { 974 sched_bind(td, old_cpu); 975 } else { 976 /* get thread back to initial CPU, if any */ 977 if (old_pinned != 0) 978 sched_bind(td, old_cpu); 979 sched_unbind(td); 980 } 981 /* restore pinned after bind */ 982 td->td_pinned = old_pinned; 983 984 thread_unlock(td); 985 986 while (epoch->e_drain_count != 0) 987 msleep(epoch, &epoch->e_drain_mtx, PZERO, "EDRAIN", 0); 988 989 mtx_unlock(&epoch->e_drain_mtx); 990 sx_xunlock(&epoch->e_drain_sx); 991 992 PICKUP_GIANT(); 993 }
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