FreeBSD/Linux Kernel Cross Reference
sys/kern/subr_epoch.c
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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