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/types.h>
  34 #include <sys/systm.h>
  35 #include <sys/counter.h>
  36 #include <sys/epoch.h>
  37 #include <sys/gtaskqueue.h>
  38 #include <sys/kernel.h>
  39 #include <sys/limits.h>
  40 #include <sys/lock.h>
  41 #include <sys/malloc.h>
  42 #include <sys/mutex.h>
  43 #include <sys/pcpu.h>
  44 #include <sys/proc.h>
  45 #include <sys/sched.h>
  46 #include <sys/sx.h>
  47 #include <sys/smp.h>
  48 #include <sys/sysctl.h>
  49 #include <sys/turnstile.h>
  50 #include <vm/vm.h>
  51 #include <vm/vm_extern.h>
  52 #include <vm/vm_kern.h>
  53 #include <vm/uma.h>
  54
  55 #include <ck_epoch.h>
  56
  57 static MALLOC_DEFINE(M_EPOCH, "epoch", "epoch based reclamation");
  58
  59 #ifdef __amd64__
  60 #define EPOCH_ALIGN CACHE_LINE_SIZE*2
  61 #else
  62 #define EPOCH_ALIGN CACHE_LINE_SIZE
  63 #endif
  64
  65 TAILQ_HEAD (epoch_tdlist, epoch_tracker);
  66 typedef struct epoch_record {
  67         ck_epoch_record_t er_record;
  68         struct epoch_context er_drain_ctx;
  69         struct epoch *er_parent;
  70         volatile struct epoch_tdlist er_tdlist;
  71         volatile uint32_t er_gen;
  72         uint32_t er_cpuid;
  73 } __aligned(EPOCH_ALIGN)     *epoch_record_t;
  74
  75 struct epoch {
  76         struct ck_epoch e_epoch __aligned(EPOCH_ALIGN);
  77         epoch_record_t e_pcpu_record;
  78         int     e_idx;
  79         int     e_flags;
  80         struct sx e_drain_sx;
  81         struct mtx e_drain_mtx;
  82         volatile int e_drain_count;
  83 };
  84
  85 /* arbitrary --- needs benchmarking */
  86 #define MAX_ADAPTIVE_SPIN 100
  87 #define MAX_EPOCHS 64
  88
  89 CTASSERT(sizeof(ck_epoch_entry_t) == sizeof(struct epoch_context));
  90 SYSCTL_NODE(_kern, OID_AUTO, epoch, CTLFLAG_RW, 0, "epoch information");
  91 SYSCTL_NODE(_kern_epoch, OID_AUTO, stats, CTLFLAG_RW, 0, "epoch stats");
  92
  93 /* Stats. */
  94 static counter_u64_t block_count;
  95
  96 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, nblocked, CTLFLAG_RW,
  97     &block_count, "# of times a thread was in an epoch when epoch_wait was called");
  98 static counter_u64_t migrate_count;
  99
 100 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, migrations, CTLFLAG_RW,
 101     &migrate_count, "# of times thread was migrated to another CPU in epoch_wait");
 102 static counter_u64_t turnstile_count;
 103
 104 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, ncontended, CTLFLAG_RW,
 105     &turnstile_count, "# of times a thread was blocked on a lock in an epoch during an epoch_wait");
 106 static counter_u64_t switch_count;
 107
 108 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, switches, CTLFLAG_RW,
 109     &switch_count, "# of times a thread voluntarily context switched in epoch_wait");
 110 static counter_u64_t epoch_call_count;
 111
 112 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, epoch_calls, CTLFLAG_RW,
 113     &epoch_call_count, "# of times a callback was deferred");
 114 static counter_u64_t epoch_call_task_count;
 115
 116 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, epoch_call_tasks, CTLFLAG_RW,
 117     &epoch_call_task_count, "# of times a callback task was run");
 118
 119 TAILQ_HEAD (threadlist, thread);
 120
 121 CK_STACK_CONTAINER(struct ck_epoch_entry, stack_entry,
 122     ck_epoch_entry_container)
 123
 124 epoch_t allepochs[MAX_EPOCHS];
 125
 126 DPCPU_DEFINE(struct grouptask, epoch_cb_task);
 127 DPCPU_DEFINE(int, epoch_cb_count);
 128
 129 static __read_mostly int inited;
 130 static __read_mostly int epoch_count;
 131 __read_mostly epoch_t global_epoch;
 132 __read_mostly epoch_t global_epoch_preempt;
 133
 134 static void epoch_call_task(void *context __unused);
 135 static  uma_zone_t pcpu_zone_record;
 136
 137 static void
 138 epoch_init(void *arg __unused)
 139 {
 140         int cpu;
 141
 142         block_count = counter_u64_alloc(M_WAITOK);
 143         migrate_count = counter_u64_alloc(M_WAITOK);
 144         turnstile_count = counter_u64_alloc(M_WAITOK);
 145         switch_count = counter_u64_alloc(M_WAITOK);
 146         epoch_call_count = counter_u64_alloc(M_WAITOK);
 147         epoch_call_task_count = counter_u64_alloc(M_WAITOK);
 148
 149         pcpu_zone_record = uma_zcreate("epoch_record pcpu",
 150             sizeof(struct epoch_record), NULL, NULL, NULL, NULL,
 151             UMA_ALIGN_PTR, UMA_ZONE_PCPU);
 152         CPU_FOREACH(cpu) {
 153                 GROUPTASK_INIT(DPCPU_ID_PTR(cpu, epoch_cb_task), 0,
 154                     epoch_call_task, NULL);
 155                 taskqgroup_attach_cpu(qgroup_softirq,
 156                     DPCPU_ID_PTR(cpu, epoch_cb_task), NULL, cpu, NULL, NULL,
 157                     "epoch call task");
 158         }
 159         inited = 1;
 160         global_epoch = epoch_alloc(0);
 161         global_epoch_preempt = epoch_alloc(EPOCH_PREEMPT);
 162 }
 163 SYSINIT(epoch, SI_SUB_TASKQ + 1, SI_ORDER_FIRST, epoch_init, NULL);
 164
 165 #if !defined(EARLY_AP_STARTUP)
 166 static void
 167 epoch_init_smp(void *dummy __unused)
 168 {
 169         inited = 2;
 170 }
 171 SYSINIT(epoch_smp, SI_SUB_SMP + 1, SI_ORDER_FIRST, epoch_init_smp, NULL);
 172 #endif
 173
 174 static void
 175 epoch_ctor(epoch_t epoch)
 176 {
 177         epoch_record_t er;
 178         int cpu;
 179
 180         epoch->e_pcpu_record = uma_zalloc_pcpu(pcpu_zone_record, M_WAITOK);
 181         CPU_FOREACH(cpu) {
 182                 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu);
 183                 bzero(er, sizeof(*er));
 184                 ck_epoch_register(&epoch->e_epoch, &er->er_record, NULL);
 185                 TAILQ_INIT((struct threadlist *)(uintptr_t)&er->er_tdlist);
 186                 er->er_cpuid = cpu;
 187                 er->er_parent = epoch;
 188         }
 189 }
 190
 191 static void
 192 epoch_adjust_prio(struct thread *td, u_char prio)
 193 {
 194
 195         thread_lock(td);
 196         sched_prio(td, prio);
 197         thread_unlock(td);
 198 }
 199
 200 epoch_t
 201 epoch_alloc(int flags)
 202 {
 203         epoch_t epoch;
 204
 205         if (__predict_false(!inited))
 206                 panic("%s called too early in boot", __func__);
 207         epoch = malloc(sizeof(struct epoch), M_EPOCH, M_ZERO | M_WAITOK);
 208         ck_epoch_init(&epoch->e_epoch);
 209         epoch_ctor(epoch);
 210         MPASS(epoch_count < MAX_EPOCHS - 2);
 211         epoch->e_flags = flags;
 212         epoch->e_idx = epoch_count;
 213         sx_init(&epoch->e_drain_sx, "epoch-drain-sx");
 214         mtx_init(&epoch->e_drain_mtx, "epoch-drain-mtx", NULL, MTX_DEF);
 215         allepochs[epoch_count++] = epoch;
 216         return (epoch);
 217 }
 218
 219 void
 220 epoch_free(epoch_t epoch)
 221 {
 222
 223         epoch_drain_callbacks(epoch);
 224         allepochs[epoch->e_idx] = NULL;
 225         epoch_wait(global_epoch);
 226         uma_zfree_pcpu(pcpu_zone_record, epoch->e_pcpu_record);
 227         mtx_destroy(&epoch->e_drain_mtx);
 228         sx_destroy(&epoch->e_drain_sx);
 229         free(epoch, M_EPOCH);
 230 }
 231
 232 static epoch_record_t
 233 epoch_currecord(epoch_t epoch)
 234 {
 235
 236         return (zpcpu_get_cpu(epoch->e_pcpu_record, curcpu));
 237 }
 238
 239 #define INIT_CHECK(epoch)                                       \
 240         do {                                                    \
 241                 if (__predict_false((epoch) == NULL))           \
 242                         return;                                 \
 243         } while (0)
 244
 245 void
 246 epoch_enter_preempt(epoch_t epoch, epoch_tracker_t et)
 247 {
 248         struct epoch_record *er;
 249         struct thread *td;
 250
 251         MPASS(cold || epoch != NULL);
 252         INIT_CHECK(epoch);
 253         MPASS(epoch->e_flags & EPOCH_PREEMPT);
 254 #ifdef EPOCH_TRACKER_DEBUG
 255         et->et_magic_pre = EPOCH_MAGIC0;
 256         et->et_magic_post = EPOCH_MAGIC1;
 257 #endif
 258         td = curthread;
 259         et->et_td = td;
 260         td->td_epochnest++;
 261         critical_enter();
 262         sched_pin();
 263
 264         td->td_pre_epoch_prio = td->td_priority;
 265         er = epoch_currecord(epoch);
 266         TAILQ_INSERT_TAIL(&er->er_tdlist, et, et_link);
 267         ck_epoch_begin(&er->er_record, &et->et_section);
 268         critical_exit();
 269 }
 270
 271 void
 272 epoch_enter(epoch_t epoch)
 273 {
 274         struct thread *td;
 275         epoch_record_t er;
 276
 277         MPASS(cold || epoch != NULL);
 278         INIT_CHECK(epoch);
 279         td = curthread;
 280
 281         td->td_epochnest++;
 282         critical_enter();
 283         er = epoch_currecord(epoch);
 284         ck_epoch_begin(&er->er_record, NULL);
 285 }
 286
 287 void
 288 epoch_exit_preempt(epoch_t epoch, epoch_tracker_t et)
 289 {
 290         struct epoch_record *er;
 291         struct thread *td;
 292
 293         INIT_CHECK(epoch);
 294         td = curthread;
 295         critical_enter();
 296         sched_unpin();
 297         MPASS(td->td_epochnest);
 298         td->td_epochnest--;
 299         er = epoch_currecord(epoch);
 300         MPASS(epoch->e_flags & EPOCH_PREEMPT);
 301         MPASS(et != NULL);
 302         MPASS(et->et_td == td);
 303 #ifdef EPOCH_TRACKER_DEBUG
 304         MPASS(et->et_magic_pre == EPOCH_MAGIC0);
 305         MPASS(et->et_magic_post == EPOCH_MAGIC1);
 306         et->et_magic_pre = 0;
 307         et->et_magic_post = 0;
 308 #endif
 309 #ifdef INVARIANTS
 310         et->et_td = (void*)0xDEADBEEF;
 311 #endif
 312         ck_epoch_end(&er->er_record, &et->et_section);
 313         TAILQ_REMOVE(&er->er_tdlist, et, et_link);
 314         er->er_gen++;
 315         if (__predict_false(td->td_pre_epoch_prio != td->td_priority))
 316                 epoch_adjust_prio(td, td->td_pre_epoch_prio);
 317         critical_exit();
 318 }
 319
 320 void
 321 epoch_exit(epoch_t epoch)
 322 {
 323         struct thread *td;
 324         epoch_record_t er;
 325
 326         INIT_CHECK(epoch);
 327         td = curthread;
 328         MPASS(td->td_epochnest);
 329         td->td_epochnest--;
 330         er = epoch_currecord(epoch);
 331         ck_epoch_end(&er->er_record, NULL);
 332         critical_exit();
 333 }
 334
 335 /*
 336  * epoch_block_handler_preempt() is a callback from the CK code when another
 337  * thread is currently in an epoch section.
 338  */
 339 static void
 340 epoch_block_handler_preempt(struct ck_epoch *global __unused,
 341     ck_epoch_record_t *cr, void *arg __unused)
 342 {
 343         epoch_record_t record;
 344         struct thread *td, *owner, *curwaittd;
 345         struct epoch_tracker *tdwait;
 346         struct turnstile *ts;
 347         struct lock_object *lock;
 348         int spincount, gen;
 349         int locksheld __unused;
 350
 351         record = __containerof(cr, struct epoch_record, er_record);
 352         td = curthread;
 353         locksheld = td->td_locks;
 354         spincount = 0;
 355         counter_u64_add(block_count, 1);
 356         /*
 357          * We lost a race and there's no longer any threads
 358          * on the CPU in an epoch section.
 359          */
 360         if (TAILQ_EMPTY(&record->er_tdlist))
 361                 return;
 362
 363         if (record->er_cpuid != curcpu) {
 364                 /*
 365                  * If the head of the list is running, we can wait for it
 366                  * to remove itself from the list and thus save us the
 367                  * overhead of a migration
 368                  */
 369                 gen = record->er_gen;
 370                 thread_unlock(td);
 371                 /*
 372                  * We can't actually check if the waiting thread is running
 373                  * so we simply poll for it to exit before giving up and
 374                  * migrating.
 375                  */
 376                 do {
 377                         cpu_spinwait();
 378                 } while (!TAILQ_EMPTY(&record->er_tdlist) &&
 379                                  gen == record->er_gen &&
 380                                  spincount++ < MAX_ADAPTIVE_SPIN);
 381                 thread_lock(td);
 382                 /*
 383                  * If the generation has changed we can poll again
 384                  * otherwise we need to migrate.
 385                  */
 386                 if (gen != record->er_gen)
 387                         return;
 388                 /*
 389                  * Being on the same CPU as that of the record on which
 390                  * we need to wait allows us access to the thread
 391                  * list associated with that CPU. We can then examine the
 392                  * oldest thread in the queue and wait on its turnstile
 393                  * until it resumes and so on until a grace period
 394                  * elapses.
 395                  *
 396                  */
 397                 counter_u64_add(migrate_count, 1);
 398                 sched_bind(td, record->er_cpuid);
 399                 /*
 400                  * At this point we need to return to the ck code
 401                  * to scan to see if a grace period has elapsed.
 402                  * We can't move on to check the thread list, because
 403                  * in the meantime new threads may have arrived that
 404                  * in fact belong to a different epoch.
 405                  */
 406                 return;
 407         }
 408         /*
 409          * Try to find a thread in an epoch section on this CPU
 410          * waiting on a turnstile. Otherwise find the lowest
 411          * priority thread (highest prio value) and drop our priority
 412          * to match to allow it to run.
 413          */
 414         TAILQ_FOREACH(tdwait, &record->er_tdlist, et_link) {
 415                 /*
 416                  * Propagate our priority to any other waiters to prevent us
 417                  * from starving them. They will have their original priority
 418                  * restore on exit from epoch_wait().
 419                  */
 420                 curwaittd = tdwait->et_td;
 421                 if (!TD_IS_INHIBITED(curwaittd) && curwaittd->td_priority > td->td_priority) {
 422                         critical_enter();
 423                         thread_unlock(td);
 424                         thread_lock(curwaittd);
 425                         sched_prio(curwaittd, td->td_priority);
 426                         thread_unlock(curwaittd);
 427                         thread_lock(td);
 428                         critical_exit();
 429                 }
 430                 if (TD_IS_INHIBITED(curwaittd) && TD_ON_LOCK(curwaittd) &&
 431                     ((ts = curwaittd->td_blocked) != NULL)) {
 432                         /*
 433                          * We unlock td to allow turnstile_wait to reacquire
 434                          * the thread lock. Before unlocking it we enter a
 435                          * critical section to prevent preemption after we
 436                          * reenable interrupts by dropping the thread lock in
 437                          * order to prevent curwaittd from getting to run.
 438                          */
 439                         critical_enter();
 440                         thread_unlock(td);
 441
 442                         if (turnstile_lock(ts, &lock, &owner)) {
 443                                 if (ts == curwaittd->td_blocked) {
 444                                         MPASS(TD_IS_INHIBITED(curwaittd) &&
 445                                             TD_ON_LOCK(curwaittd));
 446                                         critical_exit();
 447                                         turnstile_wait(ts, owner,
 448                                             curwaittd->td_tsqueue);
 449                                         counter_u64_add(turnstile_count, 1);
 450                                         thread_lock(td);
 451                                         return;
 452                                 }
 453                                 turnstile_unlock(ts, lock);
 454                         }
 455                         thread_lock(td);
 456                         critical_exit();
 457                         KASSERT(td->td_locks == locksheld,
 458                             ("%d extra locks held", td->td_locks - locksheld));
 459                 }
 460         }
 461         /*
 462          * We didn't find any threads actually blocked on a lock
 463          * so we have nothing to do except context switch away.
 464          */
 465         counter_u64_add(switch_count, 1);
 466         mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
 467
 468         /*
 469          * Release the thread lock while yielding to
 470          * allow other threads to acquire the lock
 471          * pointed to by TDQ_LOCKPTR(td). Else a
 472          * deadlock like situation might happen. (HPS)
 473          */
 474         thread_unlock(td);
 475         thread_lock(td);
 476 }
 477
 478 void
 479 epoch_wait_preempt(epoch_t epoch)
 480 {
 481         struct thread *td;
 482         int was_bound;
 483         int old_cpu;
 484         int old_pinned;
 485         u_char old_prio;
 486         int locks __unused;
 487
 488         MPASS(cold || epoch != NULL);
 489         INIT_CHECK(epoch);
 490         td = curthread;
 491 #ifdef INVARIANTS
 492         locks = curthread->td_locks;
 493         MPASS(epoch->e_flags & EPOCH_PREEMPT);
 494         if ((epoch->e_flags & EPOCH_LOCKED) == 0)
 495                 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
 496                     "epoch_wait() can be long running");
 497         KASSERT(!in_epoch(epoch), ("epoch_wait_preempt() called in the middle "
 498             "of an epoch section of the same epoch"));
 499 #endif
 500         thread_lock(td);
 501         DROP_GIANT();
 502
 503         old_cpu = PCPU_GET(cpuid);
 504         old_pinned = td->td_pinned;
 505         old_prio = td->td_priority;
 506         was_bound = sched_is_bound(td);
 507         sched_unbind(td);
 508         td->td_pinned = 0;
 509         sched_bind(td, old_cpu);
 510
 511         ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler_preempt,
 512             NULL);
 513
 514         /* restore CPU binding, if any */
 515         if (was_bound != 0) {
 516                 sched_bind(td, old_cpu);
 517         } else {
 518                 /* get thread back to initial CPU, if any */
 519                 if (old_pinned != 0)
 520                         sched_bind(td, old_cpu);
 521                 sched_unbind(td);
 522         }
 523         /* restore pinned after bind */
 524         td->td_pinned = old_pinned;
 525
 526         /* restore thread priority */
 527         sched_prio(td, old_prio);
 528         thread_unlock(td);
 529         PICKUP_GIANT();
 530         KASSERT(td->td_locks == locks,
 531             ("%d residual locks held", td->td_locks - locks));
 532 }
 533
 534 static void
 535 epoch_block_handler(struct ck_epoch *g __unused, ck_epoch_record_t *c __unused,
 536     void *arg __unused)
 537 {
 538         cpu_spinwait();
 539 }
 540
 541 void
 542 epoch_wait(epoch_t epoch)
 543 {
 544
 545         MPASS(cold || epoch != NULL);
 546         INIT_CHECK(epoch);
 547         MPASS(epoch->e_flags == 0);
 548         critical_enter();
 549         ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler, NULL);
 550         critical_exit();
 551 }
 552
 553 void
 554 epoch_call(epoch_t epoch, epoch_context_t ctx, void (*callback) (epoch_context_t))
 555 {
 556         epoch_record_t er;
 557         ck_epoch_entry_t *cb;
 558
 559         cb = (void *)ctx;
 560
 561         MPASS(callback);
 562         /* too early in boot to have epoch set up */
 563         if (__predict_false(epoch == NULL))
 564                 goto boottime;
 565 #if !defined(EARLY_AP_STARTUP)
 566         if (__predict_false(inited < 2))
 567                 goto boottime;
 568 #endif
 569
 570         critical_enter();
 571         *DPCPU_PTR(epoch_cb_count) += 1;
 572         er = epoch_currecord(epoch);
 573         ck_epoch_call(&er->er_record, cb, (ck_epoch_cb_t *)callback);
 574         critical_exit();
 575         return;
 576 boottime:
 577         callback(ctx);
 578 }
 579
 580 static void
 581 epoch_call_task(void *arg __unused)
 582 {
 583         ck_stack_entry_t *cursor, *head, *next;
 584         ck_epoch_record_t *record;
 585         epoch_record_t er;
 586         epoch_t epoch;
 587         ck_stack_t cb_stack;
 588         int i, npending, total;
 589
 590         ck_stack_init(&cb_stack);
 591         critical_enter();
 592         epoch_enter(global_epoch);
 593         for (total = i = 0; i < epoch_count; i++) {
 594                 if (__predict_false((epoch = allepochs[i]) == NULL))
 595                         continue;
 596                 er = epoch_currecord(epoch);
 597                 record = &er->er_record;
 598                 if ((npending = record->n_pending) == 0)
 599                         continue;
 600                 ck_epoch_poll_deferred(record, &cb_stack);
 601                 total += npending - record->n_pending;
 602         }
 603         epoch_exit(global_epoch);
 604         *DPCPU_PTR(epoch_cb_count) -= total;
 605         critical_exit();
 606
 607         counter_u64_add(epoch_call_count, total);
 608         counter_u64_add(epoch_call_task_count, 1);
 609
 610         head = ck_stack_batch_pop_npsc(&cb_stack);
 611         for (cursor = head; cursor != NULL; cursor = next) {
 612                 struct ck_epoch_entry *entry =
 613                     ck_epoch_entry_container(cursor);
 614
 615                 next = CK_STACK_NEXT(cursor);
 616                 entry->function(entry);
 617         }
 618 }
 619
 620 int
 621 in_epoch_verbose(epoch_t epoch, int dump_onfail)
 622 {
 623         struct epoch_tracker *tdwait;
 624         struct thread *td;
 625         epoch_record_t er;
 626
 627         td = curthread;
 628         if (td->td_epochnest == 0)
 629                 return (0);
 630         if (__predict_false((epoch) == NULL))
 631                 return (0);
 632         critical_enter();
 633         er = epoch_currecord(epoch);
 634         TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link)
 635                 if (tdwait->et_td == td) {
 636                         critical_exit();
 637                         return (1);
 638                 }
 639 #ifdef INVARIANTS
 640         if (dump_onfail) {
 641                 MPASS(td->td_pinned);
 642                 printf("cpu: %d id: %d\n", curcpu, td->td_tid);
 643                 TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link)
 644                         printf("td_tid: %d ", tdwait->et_td->td_tid);
 645                 printf("\n");
 646         }
 647 #endif
 648         critical_exit();
 649         return (0);
 650 }
 651
 652 int
 653 in_epoch(epoch_t epoch)
 654 {
 655         return (in_epoch_verbose(epoch, 0));
 656 }
 657
 658 static void
 659 epoch_drain_cb(struct epoch_context *ctx)
 660 {
 661         struct epoch *epoch =
 662             __containerof(ctx, struct epoch_record, er_drain_ctx)->er_parent;
 663
 664         if (atomic_fetchadd_int(&epoch->e_drain_count, -1) == 1) {
 665                 mtx_lock(&epoch->e_drain_mtx);
 666                 wakeup(epoch);
 667                 mtx_unlock(&epoch->e_drain_mtx);
 668         }
 669 }
 670
 671 void
 672 epoch_drain_callbacks(epoch_t epoch)
 673 {
 674         epoch_record_t er;
 675         struct thread *td;
 676         int was_bound;
 677         int old_pinned;
 678         int old_cpu;
 679         int cpu;
 680
 681         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
 682             "epoch_drain_callbacks() may sleep!");
 683
 684         /* too early in boot to have epoch set up */
 685         if (__predict_false(epoch == NULL))
 686                 return;
 687 #if !defined(EARLY_AP_STARTUP)
 688         if (__predict_false(inited < 2))
 689                 return;
 690 #endif
 691         DROP_GIANT();
 692
 693         sx_xlock(&epoch->e_drain_sx);
 694         mtx_lock(&epoch->e_drain_mtx);
 695
 696         td = curthread;
 697         thread_lock(td);
 698         old_cpu = PCPU_GET(cpuid);
 699         old_pinned = td->td_pinned;
 700         was_bound = sched_is_bound(td);
 701         sched_unbind(td);
 702         td->td_pinned = 0;
 703
 704         CPU_FOREACH(cpu)
 705                 epoch->e_drain_count++;
 706         CPU_FOREACH(cpu) {
 707                 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu);
 708                 sched_bind(td, cpu);
 709                 epoch_call(epoch, &er->er_drain_ctx, &epoch_drain_cb);
 710         }
 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         thread_unlock(td);
 725
 726         while (epoch->e_drain_count != 0)
 727                 msleep(epoch, &epoch->e_drain_mtx, PZERO, "EDRAIN", 0);
 728
 729         mtx_unlock(&epoch->e_drain_mtx);
 730         sx_xunlock(&epoch->e_drain_sx);
 731
 732         PICKUP_GIANT();
 733 }
 734
 735 void
 736 epoch_thread_init(struct thread *td)
 737 {
 738
 739         td->td_et = malloc(sizeof(struct epoch_tracker), M_EPOCH, M_WAITOK);
 740 }
 741
 742 void
 743 epoch_thread_fini(struct thread *td)
 744 {
 745
 746         free(td->td_et, M_EPOCH);
 747 }