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 #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                         continue;
 225                 epoch_trace_report("Recursively entering epoch %s "
 226                     "at %s:%d, previously entered at %s:%d\n",
 227                     epoch->e_name, file, line,
 228                     iet->et_file, iet->et_line);
 229         }
 230         et->et_epoch = epoch;
 231         et->et_file = file;
 232         et->et_line = line;
 233         SLIST_INSERT_HEAD(&td->td_epochs, et, et_tlink);
 234 }
 235
 236 static inline void
 237 epoch_trace_exit(struct thread *td, epoch_t epoch, epoch_tracker_t et,
 238     const char *file, int line)
 239 {
 240
 241         if (SLIST_FIRST(&td->td_epochs) != et) {
 242                 epoch_trace_report("Exiting epoch %s in a not nested order "
 243                     "at %s:%d. Most recently entered %s at %s:%d\n",
 244                     epoch->e_name,
 245                     file, line,
 246                     SLIST_FIRST(&td->td_epochs)->et_epoch->e_name,
 247                     SLIST_FIRST(&td->td_epochs)->et_file,
 248                     SLIST_FIRST(&td->td_epochs)->et_line);
 249                 /* This will panic if et is not anywhere on td_epochs. */
 250                 SLIST_REMOVE(&td->td_epochs, et, epoch_tracker, et_tlink);
 251         } else
 252                 SLIST_REMOVE_HEAD(&td->td_epochs, et_tlink);
 253 }
 254
 255 /* Used by assertions that check thread state before going to sleep. */
 256 void
 257 epoch_trace_list(struct thread *td)
 258 {
 259         epoch_tracker_t iet;
 260
 261         SLIST_FOREACH(iet, &td->td_epochs, et_tlink)
 262                 printf("Epoch %s entered at %s:%d\n", iet->et_epoch->e_name,
 263                     iet->et_file, iet->et_line);
 264 }
 265 #endif /* EPOCH_TRACE */
 266
 267 static void
 268 epoch_init(void *arg __unused)
 269 {
 270         int cpu;
 271
 272         block_count = counter_u64_alloc(M_WAITOK);
 273         migrate_count = counter_u64_alloc(M_WAITOK);
 274         turnstile_count = counter_u64_alloc(M_WAITOK);
 275         switch_count = counter_u64_alloc(M_WAITOK);
 276         epoch_call_count = counter_u64_alloc(M_WAITOK);
 277         epoch_call_task_count = counter_u64_alloc(M_WAITOK);
 278
 279         pcpu_zone_record = uma_zcreate("epoch_record pcpu",
 280             sizeof(struct epoch_record), NULL, NULL, NULL, NULL,
 281             UMA_ALIGN_PTR, UMA_ZONE_PCPU);
 282         CPU_FOREACH(cpu) {
 283                 GROUPTASK_INIT(DPCPU_ID_PTR(cpu, epoch_cb_task), 0,
 284                     epoch_call_task, NULL);
 285                 taskqgroup_attach_cpu(qgroup_softirq,
 286                     DPCPU_ID_PTR(cpu, epoch_cb_task), NULL, cpu, NULL, NULL,
 287                     "epoch call task");
 288         }
 289 #ifdef EPOCH_TRACE
 290         SLIST_INIT(&thread0.td_epochs);
 291 #endif
 292         sx_init(&epoch_sx, "epoch-sx");
 293         inited = 1;
 294         global_epoch = epoch_alloc("Global", 0);
 295         global_epoch_preempt = epoch_alloc("Global preemptible", EPOCH_PREEMPT);
 296 }
 297 SYSINIT(epoch, SI_SUB_EPOCH, SI_ORDER_FIRST, epoch_init, NULL);
 298
 299 #if !defined(EARLY_AP_STARTUP)
 300 static void
 301 epoch_init_smp(void *dummy __unused)
 302 {
 303         inited = 2;
 304 }
 305 SYSINIT(epoch_smp, SI_SUB_SMP + 1, SI_ORDER_FIRST, epoch_init_smp, NULL);
 306 #endif
 307
 308 static void
 309 epoch_ctor(epoch_t epoch)
 310 {
 311         epoch_record_t er;
 312         int cpu;
 313
 314         epoch->e_pcpu_record = uma_zalloc_pcpu(pcpu_zone_record, M_WAITOK);
 315         CPU_FOREACH(cpu) {
 316                 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu);
 317                 bzero(er, sizeof(*er));
 318                 ck_epoch_register(&epoch->e_epoch, &er->er_record, NULL);
 319                 TAILQ_INIT((struct threadlist *)(uintptr_t)&er->er_tdlist);
 320                 er->er_cpuid = cpu;
 321                 er->er_parent = epoch;
 322         }
 323 }
 324
 325 static void
 326 epoch_adjust_prio(struct thread *td, u_char prio)
 327 {
 328
 329         thread_lock(td);
 330         sched_prio(td, prio);
 331         thread_unlock(td);
 332 }
 333
 334 epoch_t
 335 epoch_alloc(const char *name, int flags)
 336 {
 337         epoch_t epoch;
 338         int i;
 339
 340         MPASS(name != NULL);
 341
 342         if (__predict_false(!inited))
 343                 panic("%s called too early in boot", __func__);
 344
 345         EPOCH_LOCK();
 346
 347         /*
 348          * Find a free index in the epoch array. If no free index is
 349          * found, try to use the index after the last one.
 350          */
 351         for (i = 0;; i++) {
 352                 /*
 353                  * If too many epochs are currently allocated,
 354                  * return NULL.
 355                  */
 356                 if (i == MAX_EPOCHS) {
 357                         epoch = NULL;
 358                         goto done;
 359                 }
 360                 if (epoch_array[i].e_in_use == 0)
 361                         break;
 362         }
 363
 364         epoch = epoch_array + i;
 365         ck_epoch_init(&epoch->e_epoch);
 366         epoch_ctor(epoch);
 367         epoch->e_flags = flags;
 368         epoch->e_name = name;
 369         sx_init(&epoch->e_drain_sx, "epoch-drain-sx");
 370         mtx_init(&epoch->e_drain_mtx, "epoch-drain-mtx", NULL, MTX_DEF);
 371
 372         /*
 373          * Set e_in_use last, because when this field is set the
 374          * epoch_call_task() function will start scanning this epoch
 375          * structure.
 376          */
 377         atomic_store_rel_int(&epoch->e_in_use, 1);
 378 done:
 379         EPOCH_UNLOCK();
 380         return (epoch);
 381 }
 382
 383 void
 384 epoch_free(epoch_t epoch)
 385 {
 386 #ifdef INVARIANTS
 387         int cpu;
 388 #endif
 389
 390         EPOCH_LOCK();
 391
 392         MPASS(epoch->e_in_use != 0);
 393
 394         epoch_drain_callbacks(epoch);
 395
 396         atomic_store_rel_int(&epoch->e_in_use, 0);
 397         /*
 398          * Make sure the epoch_call_task() function see e_in_use equal
 399          * to zero, by calling epoch_wait() on the global_epoch:
 400          */
 401         epoch_wait(global_epoch);
 402 #ifdef INVARIANTS
 403         CPU_FOREACH(cpu) {
 404                 epoch_record_t er;
 405
 406                 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu);
 407
 408                 /*
 409                  * Sanity check: none of the records should be in use anymore.
 410                  * We drained callbacks above and freeing the pcpu records is
 411                  * imminent.
 412                  */
 413                 MPASS(er->er_td == NULL);
 414                 MPASS(TAILQ_EMPTY(&er->er_tdlist));
 415         }
 416 #endif
 417         uma_zfree_pcpu(pcpu_zone_record, epoch->e_pcpu_record);
 418         mtx_destroy(&epoch->e_drain_mtx);
 419         sx_destroy(&epoch->e_drain_sx);
 420         memset(epoch, 0, sizeof(*epoch));
 421
 422         EPOCH_UNLOCK();
 423 }
 424
 425 static epoch_record_t
 426 epoch_currecord(epoch_t epoch)
 427 {
 428
 429         return (zpcpu_get(epoch->e_pcpu_record));
 430 }
 431
 432 #define INIT_CHECK(epoch)                                       \
 433         do {                                                    \
 434                 if (__predict_false((epoch) == NULL))           \
 435                         return;                                 \
 436         } while (0)
 437
 438 void
 439 _epoch_enter_preempt(epoch_t epoch, epoch_tracker_t et EPOCH_FILE_LINE)
 440 {
 441         struct epoch_record *er;
 442         struct thread *td;
 443
 444         MPASS(cold || epoch != NULL);
 445         td = curthread;
 446         MPASS((vm_offset_t)et >= td->td_kstack &&
 447             (vm_offset_t)et + sizeof(struct epoch_tracker) <=
 448             td->td_kstack + td->td_kstack_pages * PAGE_SIZE);
 449
 450         INIT_CHECK(epoch);
 451         MPASS(epoch->e_flags & EPOCH_PREEMPT);
 452
 453 #ifdef EPOCH_TRACE
 454         epoch_trace_enter(td, epoch, et, file, line);
 455 #endif
 456         et->et_td = td;
 457         THREAD_NO_SLEEPING();
 458         critical_enter();
 459         sched_pin();
 460         et->et_old_priority = td->td_priority;
 461         er = epoch_currecord(epoch);
 462         /* Record-level tracking is reserved for non-preemptible epochs. */
 463         MPASS(er->er_td == NULL);
 464         TAILQ_INSERT_TAIL(&er->er_tdlist, et, et_link);
 465         ck_epoch_begin(&er->er_record, &et->et_section);
 466         critical_exit();
 467 }
 468
 469 void
 470 epoch_enter(epoch_t epoch)
 471 {
 472         epoch_record_t er;
 473
 474         MPASS(cold || epoch != NULL);
 475         INIT_CHECK(epoch);
 476         critical_enter();
 477         er = epoch_currecord(epoch);
 478 #ifdef INVARIANTS
 479         if (er->er_record.active == 0) {
 480                 MPASS(er->er_td == NULL);
 481                 er->er_td = curthread;
 482         } else {
 483                 /* We've recursed, just make sure our accounting isn't wrong. */
 484                 MPASS(er->er_td == curthread);
 485         }
 486 #endif
 487         ck_epoch_begin(&er->er_record, NULL);
 488 }
 489
 490 void
 491 _epoch_exit_preempt(epoch_t epoch, epoch_tracker_t et EPOCH_FILE_LINE)
 492 {
 493         struct epoch_record *er;
 494         struct thread *td;
 495
 496         INIT_CHECK(epoch);
 497         td = curthread;
 498         critical_enter();
 499         sched_unpin();
 500         THREAD_SLEEPING_OK();
 501         er = epoch_currecord(epoch);
 502         MPASS(epoch->e_flags & EPOCH_PREEMPT);
 503         MPASS(et != NULL);
 504         MPASS(et->et_td == td);
 505 #ifdef INVARIANTS
 506         et->et_td = (void*)0xDEADBEEF;
 507         /* Record-level tracking is reserved for non-preemptible epochs. */
 508         MPASS(er->er_td == NULL);
 509 #endif
 510         ck_epoch_end(&er->er_record, &et->et_section);
 511         TAILQ_REMOVE(&er->er_tdlist, et, et_link);
 512         er->er_gen++;
 513         if (__predict_false(et->et_old_priority != td->td_priority))
 514                 epoch_adjust_prio(td, et->et_old_priority);
 515         critical_exit();
 516 #ifdef EPOCH_TRACE
 517         epoch_trace_exit(td, epoch, et, file, line);
 518 #endif
 519 }
 520
 521 void
 522 epoch_exit(epoch_t epoch)
 523 {
 524         epoch_record_t er;
 525
 526         INIT_CHECK(epoch);
 527         er = epoch_currecord(epoch);
 528         ck_epoch_end(&er->er_record, NULL);
 529 #ifdef INVARIANTS
 530         MPASS(er->er_td == curthread);
 531         if (er->er_record.active == 0)
 532                 er->er_td = NULL;
 533 #endif
 534         critical_exit();
 535 }
 536
 537 /*
 538  * epoch_block_handler_preempt() is a callback from the CK code when another
 539  * thread is currently in an epoch section.
 540  */
 541 static void
 542 epoch_block_handler_preempt(struct ck_epoch *global __unused,
 543     ck_epoch_record_t *cr, void *arg __unused)
 544 {
 545         epoch_record_t record;
 546         struct thread *td, *owner, *curwaittd;
 547         struct epoch_tracker *tdwait;
 548         struct turnstile *ts;
 549         struct lock_object *lock;
 550         int spincount, gen;
 551         int locksheld __unused;
 552
 553         record = __containerof(cr, struct epoch_record, er_record);
 554         td = curthread;
 555         locksheld = td->td_locks;
 556         spincount = 0;
 557         counter_u64_add(block_count, 1);
 558         /*
 559          * We lost a race and there's no longer any threads
 560          * on the CPU in an epoch section.
 561          */
 562         if (TAILQ_EMPTY(&record->er_tdlist))
 563                 return;
 564
 565         if (record->er_cpuid != curcpu) {
 566                 /*
 567                  * If the head of the list is running, we can wait for it
 568                  * to remove itself from the list and thus save us the
 569                  * overhead of a migration
 570                  */
 571                 gen = record->er_gen;
 572                 thread_unlock(td);
 573                 /*
 574                  * We can't actually check if the waiting thread is running
 575                  * so we simply poll for it to exit before giving up and
 576                  * migrating.
 577                  */
 578                 do {
 579                         cpu_spinwait();
 580                 } while (!TAILQ_EMPTY(&record->er_tdlist) &&
 581                                  gen == record->er_gen &&
 582                                  spincount++ < MAX_ADAPTIVE_SPIN);
 583                 thread_lock(td);
 584                 /*
 585                  * If the generation has changed we can poll again
 586                  * otherwise we need to migrate.
 587                  */
 588                 if (gen != record->er_gen)
 589                         return;
 590                 /*
 591                  * Being on the same CPU as that of the record on which
 592                  * we need to wait allows us access to the thread
 593                  * list associated with that CPU. We can then examine the
 594                  * oldest thread in the queue and wait on its turnstile
 595                  * until it resumes and so on until a grace period
 596                  * elapses.
 597                  *
 598                  */
 599                 counter_u64_add(migrate_count, 1);
 600                 sched_bind(td, record->er_cpuid);
 601                 /*
 602                  * At this point we need to return to the ck code
 603                  * to scan to see if a grace period has elapsed.
 604                  * We can't move on to check the thread list, because
 605                  * in the meantime new threads may have arrived that
 606                  * in fact belong to a different epoch.
 607                  */
 608                 return;
 609         }
 610         /*
 611          * Try to find a thread in an epoch section on this CPU
 612          * waiting on a turnstile. Otherwise find the lowest
 613          * priority thread (highest prio value) and drop our priority
 614          * to match to allow it to run.
 615          */
 616         TAILQ_FOREACH(tdwait, &record->er_tdlist, et_link) {
 617                 /*
 618                  * Propagate our priority to any other waiters to prevent us
 619                  * from starving them. They will have their original priority
 620                  * restore on exit from epoch_wait().
 621                  */
 622                 curwaittd = tdwait->et_td;
 623                 if (!TD_IS_INHIBITED(curwaittd) && curwaittd->td_priority > td->td_priority) {
 624                         critical_enter();
 625                         thread_unlock(td);
 626                         thread_lock(curwaittd);
 627                         sched_prio(curwaittd, td->td_priority);
 628                         thread_unlock(curwaittd);
 629                         thread_lock(td);
 630                         critical_exit();
 631                 }
 632                 if (TD_IS_INHIBITED(curwaittd) && TD_ON_LOCK(curwaittd) &&
 633                     ((ts = curwaittd->td_blocked) != NULL)) {
 634                         /*
 635                          * We unlock td to allow turnstile_wait to reacquire
 636                          * the thread lock. Before unlocking it we enter a
 637                          * critical section to prevent preemption after we
 638                          * reenable interrupts by dropping the thread lock in
 639                          * order to prevent curwaittd from getting to run.
 640                          */
 641                         critical_enter();
 642                         thread_unlock(td);
 643
 644                         if (turnstile_lock(ts, &lock, &owner)) {
 645                                 if (ts == curwaittd->td_blocked) {
 646                                         MPASS(TD_IS_INHIBITED(curwaittd) &&
 647                                             TD_ON_LOCK(curwaittd));
 648                                         critical_exit();
 649                                         turnstile_wait(ts, owner,
 650                                             curwaittd->td_tsqueue);
 651                                         counter_u64_add(turnstile_count, 1);
 652                                         thread_lock(td);
 653                                         return;
 654                                 }
 655                                 turnstile_unlock(ts, lock);
 656                         }
 657                         thread_lock(td);
 658                         critical_exit();
 659                         KASSERT(td->td_locks == locksheld,
 660                             ("%d extra locks held", td->td_locks - locksheld));
 661                 }
 662         }
 663         /*
 664          * We didn't find any threads actually blocked on a lock
 665          * so we have nothing to do except context switch away.
 666          */
 667         counter_u64_add(switch_count, 1);
 668         mi_switch(SW_VOL | SWT_RELINQUISH);
 669         /*
 670          * It is important the thread lock is dropped while yielding
 671          * to allow other threads to acquire the lock pointed to by
 672          * TDQ_LOCKPTR(td). Currently mi_switch() will unlock the
 673          * thread lock before returning. Else a deadlock like
 674          * situation might happen.
 675          */
 676         thread_lock(td);
 677 }
 678
 679 void
 680 epoch_wait_preempt(epoch_t epoch)
 681 {
 682         struct thread *td;
 683         int was_bound;
 684         int old_cpu;
 685         int old_pinned;
 686         u_char old_prio;
 687         int locks __unused;
 688
 689         MPASS(cold || epoch != NULL);
 690         INIT_CHECK(epoch);
 691         td = curthread;
 692 #ifdef INVARIANTS
 693         locks = curthread->td_locks;
 694         MPASS(epoch->e_flags & EPOCH_PREEMPT);
 695         if ((epoch->e_flags & EPOCH_LOCKED) == 0)
 696                 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
 697                     "epoch_wait() can be long running");
 698         KASSERT(!in_epoch(epoch), ("epoch_wait_preempt() called in the middle "
 699             "of an epoch section of the same epoch"));
 700 #endif
 701         DROP_GIANT();
 702         thread_lock(td);
 703
 704         old_cpu = PCPU_GET(cpuid);
 705         old_pinned = td->td_pinned;
 706         old_prio = td->td_priority;
 707         was_bound = sched_is_bound(td);
 708         sched_unbind(td);
 709         td->td_pinned = 0;
 710         sched_bind(td, old_cpu);
 711
 712         ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler_preempt,
 713             NULL);
 714
 715         /* restore CPU binding, if any */
 716         if (was_bound != 0) {
 717                 sched_bind(td, old_cpu);
 718         } else {
 719                 /* get thread back to initial CPU, if any */
 720                 if (old_pinned != 0)
 721                         sched_bind(td, old_cpu);
 722                 sched_unbind(td);
 723         }
 724         /* restore pinned after bind */
 725         td->td_pinned = old_pinned;
 726
 727         /* restore thread priority */
 728         sched_prio(td, old_prio);
 729         thread_unlock(td);
 730         PICKUP_GIANT();
 731         KASSERT(td->td_locks == locks,
 732             ("%d residual locks held", td->td_locks - locks));
 733 }
 734
 735 static void
 736 epoch_block_handler(struct ck_epoch *g __unused, ck_epoch_record_t *c __unused,
 737     void *arg __unused)
 738 {
 739         cpu_spinwait();
 740 }
 741
 742 void
 743 epoch_wait(epoch_t epoch)
 744 {
 745
 746         MPASS(cold || epoch != NULL);
 747         INIT_CHECK(epoch);
 748         MPASS(epoch->e_flags == 0);
 749         critical_enter();
 750         ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler, NULL);
 751         critical_exit();
 752 }
 753
 754 void
 755 epoch_call(epoch_t epoch, epoch_callback_t callback, epoch_context_t ctx)
 756 {
 757         epoch_record_t er;
 758         ck_epoch_entry_t *cb;
 759
 760         cb = (void *)ctx;
 761
 762         MPASS(callback);
 763         /* too early in boot to have epoch set up */
 764         if (__predict_false(epoch == NULL))
 765                 goto boottime;
 766 #if !defined(EARLY_AP_STARTUP)
 767         if (__predict_false(inited < 2))
 768                 goto boottime;
 769 #endif
 770
 771         critical_enter();
 772         *DPCPU_PTR(epoch_cb_count) += 1;
 773         er = epoch_currecord(epoch);
 774         ck_epoch_call(&er->er_record, cb, (ck_epoch_cb_t *)callback);
 775         critical_exit();
 776         return;
 777 boottime:
 778         callback(ctx);
 779 }
 780
 781 static void
 782 epoch_call_task(void *arg __unused)
 783 {
 784         ck_stack_entry_t *cursor, *head, *next;
 785         ck_epoch_record_t *record;
 786         epoch_record_t er;
 787         epoch_t epoch;
 788         ck_stack_t cb_stack;
 789         int i, npending, total;
 790
 791         ck_stack_init(&cb_stack);
 792         critical_enter();
 793         epoch_enter(global_epoch);
 794         for (total = i = 0; i != MAX_EPOCHS; i++) {
 795                 epoch = epoch_array + i;
 796                 if (__predict_false(
 797                     atomic_load_acq_int(&epoch->e_in_use) == 0))
 798                         continue;
 799                 er = epoch_currecord(epoch);
 800                 record = &er->er_record;
 801                 if ((npending = record->n_pending) == 0)
 802                         continue;
 803                 ck_epoch_poll_deferred(record, &cb_stack);
 804                 total += npending - record->n_pending;
 805         }
 806         epoch_exit(global_epoch);
 807         *DPCPU_PTR(epoch_cb_count) -= total;
 808         critical_exit();
 809
 810         counter_u64_add(epoch_call_count, total);
 811         counter_u64_add(epoch_call_task_count, 1);
 812
 813         head = ck_stack_batch_pop_npsc(&cb_stack);
 814         for (cursor = head; cursor != NULL; cursor = next) {
 815                 struct ck_epoch_entry *entry =
 816                     ck_epoch_entry_container(cursor);
 817
 818                 next = CK_STACK_NEXT(cursor);
 819                 entry->function(entry);
 820         }
 821 }
 822
 823 static int
 824 in_epoch_verbose_preempt(epoch_t epoch, int dump_onfail)
 825 {
 826         epoch_record_t er;
 827         struct epoch_tracker *tdwait;
 828         struct thread *td;
 829
 830         MPASS(epoch != NULL);
 831         MPASS((epoch->e_flags & EPOCH_PREEMPT) != 0);
 832         td = curthread;
 833         if (THREAD_CAN_SLEEP())
 834                 return (0);
 835         critical_enter();
 836         er = epoch_currecord(epoch);
 837         TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link)
 838                 if (tdwait->et_td == td) {
 839                         critical_exit();
 840                         return (1);
 841                 }
 842 #ifdef INVARIANTS
 843         if (dump_onfail) {
 844                 MPASS(td->td_pinned);
 845                 printf("cpu: %d id: %d\n", curcpu, td->td_tid);
 846                 TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link)
 847                         printf("td_tid: %d ", tdwait->et_td->td_tid);
 848                 printf("\n");
 849         }
 850 #endif
 851         critical_exit();
 852         return (0);
 853 }
 854
 855 #ifdef INVARIANTS
 856 static void
 857 epoch_assert_nocpu(epoch_t epoch, struct thread *td)
 858 {
 859         epoch_record_t er;
 860         int cpu;
 861         bool crit;
 862
 863         crit = td->td_critnest > 0;
 864
 865         /* Check for a critical section mishap. */
 866         CPU_FOREACH(cpu) {
 867                 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu);
 868                 KASSERT(er->er_td != td,
 869                     ("%s critical section in epoch '%s', from cpu %d",
 870                     (crit ? "exited" : "re-entered"), epoch->e_name, cpu));
 871         }
 872 }
 873 #else
 874 #define epoch_assert_nocpu(e, td) do {} while (0)
 875 #endif
 876
 877 int
 878 in_epoch_verbose(epoch_t epoch, int dump_onfail)
 879 {
 880         epoch_record_t er;
 881         struct thread *td;
 882
 883         if (__predict_false((epoch) == NULL))
 884                 return (0);
 885         if ((epoch->e_flags & EPOCH_PREEMPT) != 0)
 886                 return (in_epoch_verbose_preempt(epoch, dump_onfail));
 887
 888         /*
 889          * The thread being in a critical section is a necessary
 890          * condition to be correctly inside a non-preemptible epoch,
 891          * so it's definitely not in this epoch.
 892          */
 893         td = curthread;
 894         if (td->td_critnest == 0) {
 895                 epoch_assert_nocpu(epoch, td);
 896                 return (0);
 897         }
 898
 899         /*
 900          * The current cpu is in a critical section, so the epoch record will be
 901          * stable for the rest of this function.  Knowing that the record is not
 902          * active is sufficient for knowing whether we're in this epoch or not,
 903          * since it's a pcpu record.
 904          */
 905         er = epoch_currecord(epoch);
 906         if (er->er_record.active == 0) {
 907                 epoch_assert_nocpu(epoch, td);
 908                 return (0);
 909         }
 910
 911         MPASS(er->er_td == td);
 912         return (1);
 913 }
 914
 915 int
 916 in_epoch(epoch_t epoch)
 917 {
 918         return (in_epoch_verbose(epoch, 0));
 919 }
 920
 921 static void
 922 epoch_drain_cb(struct epoch_context *ctx)
 923 {
 924         struct epoch *epoch =
 925             __containerof(ctx, struct epoch_record, er_drain_ctx)->er_parent;
 926
 927         if (atomic_fetchadd_int(&epoch->e_drain_count, -1) == 1) {
 928                 mtx_lock(&epoch->e_drain_mtx);
 929                 wakeup(epoch);
 930                 mtx_unlock(&epoch->e_drain_mtx);
 931         }
 932 }
 933
 934 void
 935 epoch_drain_callbacks(epoch_t epoch)
 936 {
 937         epoch_record_t er;
 938         struct thread *td;
 939         int was_bound;
 940         int old_pinned;
 941         int old_cpu;
 942         int cpu;
 943
 944         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
 945             "epoch_drain_callbacks() may sleep!");
 946
 947         /* too early in boot to have epoch set up */
 948         if (__predict_false(epoch == NULL))
 949                 return;
 950 #if !defined(EARLY_AP_STARTUP)
 951         if (__predict_false(inited < 2))
 952                 return;
 953 #endif
 954         DROP_GIANT();
 955
 956         sx_xlock(&epoch->e_drain_sx);
 957         mtx_lock(&epoch->e_drain_mtx);
 958
 959         td = curthread;
 960         thread_lock(td);
 961         old_cpu = PCPU_GET(cpuid);
 962         old_pinned = td->td_pinned;
 963         was_bound = sched_is_bound(td);
 964         sched_unbind(td);
 965         td->td_pinned = 0;
 966
 967         CPU_FOREACH(cpu)
 968                 epoch->e_drain_count++;
 969         CPU_FOREACH(cpu) {
 970                 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu);
 971                 sched_bind(td, cpu);
 972                 epoch_call(epoch, &epoch_drain_cb, &er->er_drain_ctx);
 973         }
 974
 975         /* restore CPU binding, if any */
 976         if (was_bound != 0) {
 977                 sched_bind(td, old_cpu);
 978         } else {
 979                 /* get thread back to initial CPU, if any */
 980                 if (old_pinned != 0)
 981                         sched_bind(td, old_cpu);
 982                 sched_unbind(td);
 983         }
 984         /* restore pinned after bind */
 985         td->td_pinned = old_pinned;
 986
 987         thread_unlock(td);
 988
 989         while (epoch->e_drain_count != 0)
 990                 msleep(epoch, &epoch->e_drain_mtx, PZERO, "EDRAIN", 0);
 991
 992         mtx_unlock(&epoch->e_drain_mtx);
 993         sx_xunlock(&epoch->e_drain_sx);
 994
 995         PICKUP_GIANT();
 996 }