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 static MALLOC_DEFINE(M_EPOCH, "epoch", "epoch based reclamation");
  62
  63 #ifdef __amd64__
  64 #define EPOCH_ALIGN CACHE_LINE_SIZE*2
  65 #else
  66 #define EPOCH_ALIGN CACHE_LINE_SIZE
  67 #endif
  68
  69 TAILQ_HEAD (epoch_tdlist, epoch_tracker);
  70 typedef struct epoch_record {
  71         ck_epoch_record_t er_record;
  72         struct epoch_context er_drain_ctx;
  73         struct epoch *er_parent;
  74         volatile struct epoch_tdlist er_tdlist;
  75         volatile uint32_t er_gen;
  76         uint32_t er_cpuid;
  77 } __aligned(EPOCH_ALIGN)     *epoch_record_t;
  78
  79 struct epoch {
  80         struct ck_epoch e_epoch __aligned(EPOCH_ALIGN);
  81         epoch_record_t e_pcpu_record;
  82         int     e_idx;
  83         int     e_flags;
  84         struct sx e_drain_sx;
  85         struct mtx e_drain_mtx;
  86         volatile int e_drain_count;
  87         const char *e_name;
  88 };
  89
  90 /* arbitrary --- needs benchmarking */
  91 #define MAX_ADAPTIVE_SPIN 100
  92 #define MAX_EPOCHS 64
  93
  94 CTASSERT(sizeof(ck_epoch_entry_t) == sizeof(struct epoch_context));
  95 SYSCTL_NODE(_kern, OID_AUTO, epoch, CTLFLAG_RW, 0, "epoch information");
  96 SYSCTL_NODE(_kern_epoch, OID_AUTO, stats, CTLFLAG_RW, 0, "epoch stats");
  97
  98 /* Stats. */
  99 static counter_u64_t block_count;
 100
 101 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, nblocked, CTLFLAG_RW,
 102     &block_count, "# of times a thread was in an epoch when epoch_wait was called");
 103 static counter_u64_t migrate_count;
 104
 105 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, migrations, CTLFLAG_RW,
 106     &migrate_count, "# of times thread was migrated to another CPU in epoch_wait");
 107 static counter_u64_t turnstile_count;
 108
 109 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, ncontended, CTLFLAG_RW,
 110     &turnstile_count, "# of times a thread was blocked on a lock in an epoch during an epoch_wait");
 111 static counter_u64_t switch_count;
 112
 113 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, switches, CTLFLAG_RW,
 114     &switch_count, "# of times a thread voluntarily context switched in epoch_wait");
 115 static counter_u64_t epoch_call_count;
 116
 117 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, epoch_calls, CTLFLAG_RW,
 118     &epoch_call_count, "# of times a callback was deferred");
 119 static counter_u64_t epoch_call_task_count;
 120
 121 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, epoch_call_tasks, CTLFLAG_RW,
 122     &epoch_call_task_count, "# of times a callback task was run");
 123
 124 TAILQ_HEAD (threadlist, thread);
 125
 126 CK_STACK_CONTAINER(struct ck_epoch_entry, stack_entry,
 127     ck_epoch_entry_container)
 128
 129 epoch_t allepochs[MAX_EPOCHS];
 130
 131 DPCPU_DEFINE(struct grouptask, epoch_cb_task);
 132 DPCPU_DEFINE(int, epoch_cb_count);
 133
 134 static __read_mostly int inited;
 135 static __read_mostly int epoch_count;
 136 __read_mostly epoch_t global_epoch;
 137 __read_mostly epoch_t global_epoch_preempt;
 138
 139 static void epoch_call_task(void *context __unused);
 140 static  uma_zone_t pcpu_zone_record;
 141
 142 #ifdef EPOCH_TRACE
 143 struct stackentry {
 144         RB_ENTRY(stackentry) se_node;
 145         struct stack se_stack;
 146 };
 147
 148 static int
 149 stackentry_compare(struct stackentry *a, struct stackentry *b)
 150 {
 151
 152         if (a->se_stack.depth > b->se_stack.depth)
 153                 return (1);
 154         if (a->se_stack.depth < b->se_stack.depth)
 155                 return (-1);
 156         for (int i = 0; i < a->se_stack.depth; i++) {
 157                 if (a->se_stack.pcs[i] > b->se_stack.pcs[i])
 158                         return (1);
 159                 if (a->se_stack.pcs[i] < b->se_stack.pcs[i])
 160                         return (-1);
 161         }
 162
 163         return (0);
 164 }
 165
 166 RB_HEAD(stacktree, stackentry) epoch_stacks = RB_INITIALIZER(&epoch_stacks);
 167 RB_GENERATE_STATIC(stacktree, stackentry, se_node, stackentry_compare);
 168
 169 static struct mtx epoch_stacks_lock;
 170 MTX_SYSINIT(epochstacks, &epoch_stacks_lock, "epoch_stacks", MTX_DEF);
 171
 172 static bool epoch_trace_stack_print = true;
 173 SYSCTL_BOOL(_kern_epoch, OID_AUTO, trace_stack_print, CTLFLAG_RWTUN,
 174     &epoch_trace_stack_print, 0, "Print stack traces on epoch reports");
 175
 176 static void epoch_trace_report(const char *fmt, ...) __printflike(1, 2);
 177 static inline void
 178 epoch_trace_report(const char *fmt, ...)
 179 {
 180         va_list ap;
 181         struct stackentry se, *new;
 182
 183         stack_zero(&se.se_stack);       /* XXX: is it really needed? */
 184         stack_save(&se.se_stack);
 185
 186         /* Tree is never reduced - go lockless. */
 187         if (RB_FIND(stacktree, &epoch_stacks, &se) != NULL)
 188                 return;
 189
 190         new = malloc(sizeof(*new), M_STACK, M_NOWAIT);
 191         if (new != NULL) {
 192                 bcopy(&se.se_stack, &new->se_stack, sizeof(struct stack));
 193
 194                 mtx_lock(&epoch_stacks_lock);
 195                 new = RB_INSERT(stacktree, &epoch_stacks, new);
 196                 mtx_unlock(&epoch_stacks_lock);
 197                 if (new != NULL)
 198                         free(new, M_STACK);
 199         }
 200
 201         va_start(ap, fmt);
 202         (void)vprintf(fmt, ap);
 203         va_end(ap);
 204         if (epoch_trace_stack_print)
 205                 stack_print_ddb(&se.se_stack);
 206 }
 207
 208 static inline void
 209 epoch_trace_enter(struct thread *td, epoch_t epoch, epoch_tracker_t et,
 210     const char *file, int line)
 211 {
 212         epoch_tracker_t iet;
 213
 214         SLIST_FOREACH(iet, &td->td_epochs, et_tlink)
 215                 if (iet->et_epoch == epoch)
 216                         epoch_trace_report("Recursively entering epoch %s "
 217                             "at %s:%d, previously entered at %s:%d\n",
 218                             epoch->e_name, file, line,
 219                             iet->et_file, iet->et_line);
 220         et->et_epoch = epoch;
 221         et->et_file = file;
 222         et->et_line = line;
 223         SLIST_INSERT_HEAD(&td->td_epochs, et, et_tlink);
 224 }
 225
 226 static inline void
 227 epoch_trace_exit(struct thread *td, epoch_t epoch, epoch_tracker_t et,
 228     const char *file, int line)
 229 {
 230
 231         if (SLIST_FIRST(&td->td_epochs) != et) {
 232                 epoch_trace_report("Exiting epoch %s in a not nested order "
 233                     "at %s:%d. Most recently entered %s at %s:%d\n",
 234                     epoch->e_name,
 235                     file, line,
 236                     SLIST_FIRST(&td->td_epochs)->et_epoch->e_name,
 237                     SLIST_FIRST(&td->td_epochs)->et_file,
 238                     SLIST_FIRST(&td->td_epochs)->et_line);
 239                 /* This will panic if et is not anywhere on td_epochs. */
 240                 SLIST_REMOVE(&td->td_epochs, et, epoch_tracker, et_tlink);
 241         } else
 242                 SLIST_REMOVE_HEAD(&td->td_epochs, et_tlink);
 243 }
 244
 245 /* Used by assertions that check thread state before going to sleep. */
 246 void
 247 epoch_trace_list(struct thread *td)
 248 {
 249         epoch_tracker_t iet;
 250
 251         SLIST_FOREACH(iet, &td->td_epochs, et_tlink)
 252                 printf("Epoch %s entered at %s:%d\n", iet->et_epoch->e_name,
 253                     iet->et_file, iet->et_line);
 254 }
 255 #endif /* EPOCH_TRACE */
 256
 257 static void
 258 epoch_init(void *arg __unused)
 259 {
 260         int cpu;
 261
 262         block_count = counter_u64_alloc(M_WAITOK);
 263         migrate_count = counter_u64_alloc(M_WAITOK);
 264         turnstile_count = counter_u64_alloc(M_WAITOK);
 265         switch_count = counter_u64_alloc(M_WAITOK);
 266         epoch_call_count = counter_u64_alloc(M_WAITOK);
 267         epoch_call_task_count = counter_u64_alloc(M_WAITOK);
 268
 269         pcpu_zone_record = uma_zcreate("epoch_record pcpu",
 270             sizeof(struct epoch_record), NULL, NULL, NULL, NULL,
 271             UMA_ALIGN_PTR, UMA_ZONE_PCPU);
 272         CPU_FOREACH(cpu) {
 273                 GROUPTASK_INIT(DPCPU_ID_PTR(cpu, epoch_cb_task), 0,
 274                     epoch_call_task, NULL);
 275                 taskqgroup_attach_cpu(qgroup_softirq,
 276                     DPCPU_ID_PTR(cpu, epoch_cb_task), NULL, cpu, NULL, NULL,
 277                     "epoch call task");
 278         }
 279 #ifdef EPOCH_TRACE
 280         SLIST_INIT(&thread0.td_epochs);
 281 #endif
 282         inited = 1;
 283         global_epoch = epoch_alloc("Global", 0);
 284         global_epoch_preempt = epoch_alloc("Global preemptible", EPOCH_PREEMPT);
 285 }
 286 SYSINIT(epoch, SI_SUB_EPOCH, SI_ORDER_FIRST, epoch_init, NULL);
 287
 288 #if !defined(EARLY_AP_STARTUP)
 289 static void
 290 epoch_init_smp(void *dummy __unused)
 291 {
 292         inited = 2;
 293 }
 294 SYSINIT(epoch_smp, SI_SUB_SMP + 1, SI_ORDER_FIRST, epoch_init_smp, NULL);
 295 #endif
 296
 297 static void
 298 epoch_ctor(epoch_t epoch)
 299 {
 300         epoch_record_t er;
 301         int cpu;
 302
 303         epoch->e_pcpu_record = uma_zalloc_pcpu(pcpu_zone_record, M_WAITOK);
 304         CPU_FOREACH(cpu) {
 305                 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu);
 306                 bzero(er, sizeof(*er));
 307                 ck_epoch_register(&epoch->e_epoch, &er->er_record, NULL);
 308                 TAILQ_INIT((struct threadlist *)(uintptr_t)&er->er_tdlist);
 309                 er->er_cpuid = cpu;
 310                 er->er_parent = epoch;
 311         }
 312 }
 313
 314 static void
 315 epoch_adjust_prio(struct thread *td, u_char prio)
 316 {
 317
 318         thread_lock(td);
 319         sched_prio(td, prio);
 320         thread_unlock(td);
 321 }
 322
 323 epoch_t
 324 epoch_alloc(const char *name, int flags)
 325 {
 326         epoch_t epoch;
 327
 328         if (__predict_false(!inited))
 329                 panic("%s called too early in boot", __func__);
 330         epoch = malloc(sizeof(struct epoch), M_EPOCH, M_ZERO | M_WAITOK);
 331         ck_epoch_init(&epoch->e_epoch);
 332         epoch_ctor(epoch);
 333         MPASS(epoch_count < MAX_EPOCHS - 2);
 334         epoch->e_flags = flags;
 335         epoch->e_idx = epoch_count;
 336         epoch->e_name = name;
 337         sx_init(&epoch->e_drain_sx, "epoch-drain-sx");
 338         mtx_init(&epoch->e_drain_mtx, "epoch-drain-mtx", NULL, MTX_DEF);
 339         allepochs[epoch_count++] = epoch;
 340         return (epoch);
 341 }
 342
 343 void
 344 epoch_free(epoch_t epoch)
 345 {
 346
 347         epoch_drain_callbacks(epoch);
 348         allepochs[epoch->e_idx] = NULL;
 349         epoch_wait(global_epoch);
 350         uma_zfree_pcpu(pcpu_zone_record, epoch->e_pcpu_record);
 351         mtx_destroy(&epoch->e_drain_mtx);
 352         sx_destroy(&epoch->e_drain_sx);
 353         free(epoch, M_EPOCH);
 354 }
 355
 356 static epoch_record_t
 357 epoch_currecord(epoch_t epoch)
 358 {
 359
 360         return (zpcpu_get_cpu(epoch->e_pcpu_record, curcpu));
 361 }
 362
 363 #define INIT_CHECK(epoch)                                       \
 364         do {                                                    \
 365                 if (__predict_false((epoch) == NULL))           \
 366                         return;                                 \
 367         } while (0)
 368
 369 void
 370 _epoch_enter_preempt(epoch_t epoch, epoch_tracker_t et EPOCH_FILE_LINE)
 371 {
 372         struct epoch_record *er;
 373         struct thread *td;
 374
 375         MPASS(cold || epoch != NULL);
 376         MPASS(epoch->e_flags & EPOCH_PREEMPT);
 377         td = curthread;
 378         MPASS((vm_offset_t)et >= td->td_kstack &&
 379             (vm_offset_t)et + sizeof(struct epoch_tracker) <=
 380             td->td_kstack + td->td_kstack_pages * PAGE_SIZE);
 381
 382         INIT_CHECK(epoch);
 383 #ifdef EPOCH_TRACE
 384         epoch_trace_enter(td, epoch, et, file, line);
 385 #endif
 386         et->et_td = td;
 387         THREAD_NO_SLEEPING();
 388         critical_enter();
 389         sched_pin();
 390         td->td_pre_epoch_prio = td->td_priority;
 391         er = epoch_currecord(epoch);
 392         TAILQ_INSERT_TAIL(&er->er_tdlist, et, et_link);
 393         ck_epoch_begin(&er->er_record, &et->et_section);
 394         critical_exit();
 395 }
 396
 397 void
 398 epoch_enter(epoch_t epoch)
 399 {
 400         epoch_record_t er;
 401
 402         MPASS(cold || epoch != NULL);
 403         INIT_CHECK(epoch);
 404         critical_enter();
 405         er = epoch_currecord(epoch);
 406         ck_epoch_begin(&er->er_record, NULL);
 407 }
 408
 409 void
 410 _epoch_exit_preempt(epoch_t epoch, epoch_tracker_t et EPOCH_FILE_LINE)
 411 {
 412         struct epoch_record *er;
 413         struct thread *td;
 414
 415         INIT_CHECK(epoch);
 416         td = curthread;
 417         critical_enter();
 418         sched_unpin();
 419         THREAD_SLEEPING_OK();
 420         er = epoch_currecord(epoch);
 421         MPASS(epoch->e_flags & EPOCH_PREEMPT);
 422         MPASS(et != NULL);
 423         MPASS(et->et_td == td);
 424 #ifdef INVARIANTS
 425         et->et_td = (void*)0xDEADBEEF;
 426 #endif
 427         ck_epoch_end(&er->er_record, &et->et_section);
 428         TAILQ_REMOVE(&er->er_tdlist, et, et_link);
 429         er->er_gen++;
 430         if (__predict_false(td->td_pre_epoch_prio != td->td_priority))
 431                 epoch_adjust_prio(td, td->td_pre_epoch_prio);
 432         critical_exit();
 433 #ifdef EPOCH_TRACE
 434         epoch_trace_exit(td, epoch, et, file, line);
 435 #endif
 436 }
 437
 438 void
 439 epoch_exit(epoch_t epoch)
 440 {
 441         epoch_record_t er;
 442
 443         INIT_CHECK(epoch);
 444         er = epoch_currecord(epoch);
 445         ck_epoch_end(&er->er_record, NULL);
 446         critical_exit();
 447 }
 448
 449 /*
 450  * epoch_block_handler_preempt() is a callback from the CK code when another
 451  * thread is currently in an epoch section.
 452  */
 453 static void
 454 epoch_block_handler_preempt(struct ck_epoch *global __unused,
 455     ck_epoch_record_t *cr, void *arg __unused)
 456 {
 457         epoch_record_t record;
 458         struct thread *td, *owner, *curwaittd;
 459         struct epoch_tracker *tdwait;
 460         struct turnstile *ts;
 461         struct lock_object *lock;
 462         int spincount, gen;
 463         int locksheld __unused;
 464
 465         record = __containerof(cr, struct epoch_record, er_record);
 466         td = curthread;
 467         locksheld = td->td_locks;
 468         spincount = 0;
 469         counter_u64_add(block_count, 1);
 470         /*
 471          * We lost a race and there's no longer any threads
 472          * on the CPU in an epoch section.
 473          */
 474         if (TAILQ_EMPTY(&record->er_tdlist))
 475                 return;
 476
 477         if (record->er_cpuid != curcpu) {
 478                 /*
 479                  * If the head of the list is running, we can wait for it
 480                  * to remove itself from the list and thus save us the
 481                  * overhead of a migration
 482                  */
 483                 gen = record->er_gen;
 484                 thread_unlock(td);
 485                 /*
 486                  * We can't actually check if the waiting thread is running
 487                  * so we simply poll for it to exit before giving up and
 488                  * migrating.
 489                  */
 490                 do {
 491                         cpu_spinwait();
 492                 } while (!TAILQ_EMPTY(&record->er_tdlist) &&
 493                                  gen == record->er_gen &&
 494                                  spincount++ < MAX_ADAPTIVE_SPIN);
 495                 thread_lock(td);
 496                 /*
 497                  * If the generation has changed we can poll again
 498                  * otherwise we need to migrate.
 499                  */
 500                 if (gen != record->er_gen)
 501                         return;
 502                 /*
 503                  * Being on the same CPU as that of the record on which
 504                  * we need to wait allows us access to the thread
 505                  * list associated with that CPU. We can then examine the
 506                  * oldest thread in the queue and wait on its turnstile
 507                  * until it resumes and so on until a grace period
 508                  * elapses.
 509                  *
 510                  */
 511                 counter_u64_add(migrate_count, 1);
 512                 sched_bind(td, record->er_cpuid);
 513                 /*
 514                  * At this point we need to return to the ck code
 515                  * to scan to see if a grace period has elapsed.
 516                  * We can't move on to check the thread list, because
 517                  * in the meantime new threads may have arrived that
 518                  * in fact belong to a different epoch.
 519                  */
 520                 return;
 521         }
 522         /*
 523          * Try to find a thread in an epoch section on this CPU
 524          * waiting on a turnstile. Otherwise find the lowest
 525          * priority thread (highest prio value) and drop our priority
 526          * to match to allow it to run.
 527          */
 528         TAILQ_FOREACH(tdwait, &record->er_tdlist, et_link) {
 529                 /*
 530                  * Propagate our priority to any other waiters to prevent us
 531                  * from starving them. They will have their original priority
 532                  * restore on exit from epoch_wait().
 533                  */
 534                 curwaittd = tdwait->et_td;
 535                 if (!TD_IS_INHIBITED(curwaittd) && curwaittd->td_priority > td->td_priority) {
 536                         critical_enter();
 537                         thread_unlock(td);
 538                         thread_lock(curwaittd);
 539                         sched_prio(curwaittd, td->td_priority);
 540                         thread_unlock(curwaittd);
 541                         thread_lock(td);
 542                         critical_exit();
 543                 }
 544                 if (TD_IS_INHIBITED(curwaittd) && TD_ON_LOCK(curwaittd) &&
 545                     ((ts = curwaittd->td_blocked) != NULL)) {
 546                         /*
 547                          * We unlock td to allow turnstile_wait to reacquire
 548                          * the thread lock. Before unlocking it we enter a
 549                          * critical section to prevent preemption after we
 550                          * reenable interrupts by dropping the thread lock in
 551                          * order to prevent curwaittd from getting to run.
 552                          */
 553                         critical_enter();
 554                         thread_unlock(td);
 555
 556                         if (turnstile_lock(ts, &lock, &owner)) {
 557                                 if (ts == curwaittd->td_blocked) {
 558                                         MPASS(TD_IS_INHIBITED(curwaittd) &&
 559                                             TD_ON_LOCK(curwaittd));
 560                                         critical_exit();
 561                                         turnstile_wait(ts, owner,
 562                                             curwaittd->td_tsqueue);
 563                                         counter_u64_add(turnstile_count, 1);
 564                                         thread_lock(td);
 565                                         return;
 566                                 }
 567                                 turnstile_unlock(ts, lock);
 568                         }
 569                         thread_lock(td);
 570                         critical_exit();
 571                         KASSERT(td->td_locks == locksheld,
 572                             ("%d extra locks held", td->td_locks - locksheld));
 573                 }
 574         }
 575         /*
 576          * We didn't find any threads actually blocked on a lock
 577          * so we have nothing to do except context switch away.
 578          */
 579         counter_u64_add(switch_count, 1);
 580         mi_switch(SW_VOL | SWT_RELINQUISH);
 581         thread_lock(td);
 582 }
 583
 584 void
 585 epoch_wait_preempt(epoch_t epoch)
 586 {
 587         struct thread *td;
 588         int was_bound;
 589         int old_cpu;
 590         int old_pinned;
 591         u_char old_prio;
 592         int locks __unused;
 593
 594         MPASS(cold || epoch != NULL);
 595         INIT_CHECK(epoch);
 596         td = curthread;
 597 #ifdef INVARIANTS
 598         locks = curthread->td_locks;
 599         MPASS(epoch->e_flags & EPOCH_PREEMPT);
 600         if ((epoch->e_flags & EPOCH_LOCKED) == 0)
 601                 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
 602                     "epoch_wait() can be long running");
 603         KASSERT(!in_epoch(epoch), ("epoch_wait_preempt() called in the middle "
 604             "of an epoch section of the same epoch"));
 605 #endif
 606         thread_lock(td);
 607         DROP_GIANT();
 608
 609         old_cpu = PCPU_GET(cpuid);
 610         old_pinned = td->td_pinned;
 611         old_prio = td->td_priority;
 612         was_bound = sched_is_bound(td);
 613         sched_unbind(td);
 614         td->td_pinned = 0;
 615         sched_bind(td, old_cpu);
 616
 617         ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler_preempt,
 618             NULL);
 619
 620         /* restore CPU binding, if any */
 621         if (was_bound != 0) {
 622                 sched_bind(td, old_cpu);
 623         } else {
 624                 /* get thread back to initial CPU, if any */
 625                 if (old_pinned != 0)
 626                         sched_bind(td, old_cpu);
 627                 sched_unbind(td);
 628         }
 629         /* restore pinned after bind */
 630         td->td_pinned = old_pinned;
 631
 632         /* restore thread priority */
 633         sched_prio(td, old_prio);
 634         thread_unlock(td);
 635         PICKUP_GIANT();
 636         KASSERT(td->td_locks == locks,
 637             ("%d residual locks held", td->td_locks - locks));
 638 }
 639
 640 static void
 641 epoch_block_handler(struct ck_epoch *g __unused, ck_epoch_record_t *c __unused,
 642     void *arg __unused)
 643 {
 644         cpu_spinwait();
 645 }
 646
 647 void
 648 epoch_wait(epoch_t epoch)
 649 {
 650
 651         MPASS(cold || epoch != NULL);
 652         INIT_CHECK(epoch);
 653         MPASS(epoch->e_flags == 0);
 654         critical_enter();
 655         ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler, NULL);
 656         critical_exit();
 657 }
 658
 659 void
 660 epoch_call(epoch_t epoch, epoch_context_t ctx, void (*callback) (epoch_context_t))
 661 {
 662         epoch_record_t er;
 663         ck_epoch_entry_t *cb;
 664
 665         cb = (void *)ctx;
 666
 667         MPASS(callback);
 668         /* too early in boot to have epoch set up */
 669         if (__predict_false(epoch == NULL))
 670                 goto boottime;
 671 #if !defined(EARLY_AP_STARTUP)
 672         if (__predict_false(inited < 2))
 673                 goto boottime;
 674 #endif
 675
 676         critical_enter();
 677         *DPCPU_PTR(epoch_cb_count) += 1;
 678         er = epoch_currecord(epoch);
 679         ck_epoch_call(&er->er_record, cb, (ck_epoch_cb_t *)callback);
 680         critical_exit();
 681         return;
 682 boottime:
 683         callback(ctx);
 684 }
 685
 686 static void
 687 epoch_call_task(void *arg __unused)
 688 {
 689         ck_stack_entry_t *cursor, *head, *next;
 690         ck_epoch_record_t *record;
 691         epoch_record_t er;
 692         epoch_t epoch;
 693         ck_stack_t cb_stack;
 694         int i, npending, total;
 695
 696         ck_stack_init(&cb_stack);
 697         critical_enter();
 698         epoch_enter(global_epoch);
 699         for (total = i = 0; i < epoch_count; i++) {
 700                 if (__predict_false((epoch = allepochs[i]) == NULL))
 701                         continue;
 702                 er = epoch_currecord(epoch);
 703                 record = &er->er_record;
 704                 if ((npending = record->n_pending) == 0)
 705                         continue;
 706                 ck_epoch_poll_deferred(record, &cb_stack);
 707                 total += npending - record->n_pending;
 708         }
 709         epoch_exit(global_epoch);
 710         *DPCPU_PTR(epoch_cb_count) -= total;
 711         critical_exit();
 712
 713         counter_u64_add(epoch_call_count, total);
 714         counter_u64_add(epoch_call_task_count, 1);
 715
 716         head = ck_stack_batch_pop_npsc(&cb_stack);
 717         for (cursor = head; cursor != NULL; cursor = next) {
 718                 struct ck_epoch_entry *entry =
 719                     ck_epoch_entry_container(cursor);
 720
 721                 next = CK_STACK_NEXT(cursor);
 722                 entry->function(entry);
 723         }
 724 }
 725
 726 int
 727 in_epoch_verbose(epoch_t epoch, int dump_onfail)
 728 {
 729         struct epoch_tracker *tdwait;
 730         struct thread *td;
 731         epoch_record_t er;
 732
 733         td = curthread;
 734         if (THREAD_CAN_SLEEP())
 735                 return (0);
 736         if (__predict_false((epoch) == NULL))
 737                 return (0);
 738         critical_enter();
 739         er = epoch_currecord(epoch);
 740         TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link)
 741                 if (tdwait->et_td == td) {
 742                         critical_exit();
 743                         return (1);
 744                 }
 745 #ifdef INVARIANTS
 746         if (dump_onfail) {
 747                 MPASS(td->td_pinned);
 748                 printf("cpu: %d id: %d\n", curcpu, td->td_tid);
 749                 TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link)
 750                         printf("td_tid: %d ", tdwait->et_td->td_tid);
 751                 printf("\n");
 752         }
 753 #endif
 754         critical_exit();
 755         return (0);
 756 }
 757
 758 int
 759 in_epoch(epoch_t epoch)
 760 {
 761         return (in_epoch_verbose(epoch, 0));
 762 }
 763
 764 static void
 765 epoch_drain_cb(struct epoch_context *ctx)
 766 {
 767         struct epoch *epoch =
 768             __containerof(ctx, struct epoch_record, er_drain_ctx)->er_parent;
 769
 770         if (atomic_fetchadd_int(&epoch->e_drain_count, -1) == 1) {
 771                 mtx_lock(&epoch->e_drain_mtx);
 772                 wakeup(epoch);
 773                 mtx_unlock(&epoch->e_drain_mtx);
 774         }
 775 }
 776
 777 void
 778 epoch_drain_callbacks(epoch_t epoch)
 779 {
 780         epoch_record_t er;
 781         struct thread *td;
 782         int was_bound;
 783         int old_pinned;
 784         int old_cpu;
 785         int cpu;
 786
 787         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
 788             "epoch_drain_callbacks() may sleep!");
 789
 790         /* too early in boot to have epoch set up */
 791         if (__predict_false(epoch == NULL))
 792                 return;
 793 #if !defined(EARLY_AP_STARTUP)
 794         if (__predict_false(inited < 2))
 795                 return;
 796 #endif
 797         DROP_GIANT();
 798
 799         sx_xlock(&epoch->e_drain_sx);
 800         mtx_lock(&epoch->e_drain_mtx);
 801
 802         td = curthread;
 803         thread_lock(td);
 804         old_cpu = PCPU_GET(cpuid);
 805         old_pinned = td->td_pinned;
 806         was_bound = sched_is_bound(td);
 807         sched_unbind(td);
 808         td->td_pinned = 0;
 809
 810         CPU_FOREACH(cpu)
 811                 epoch->e_drain_count++;
 812         CPU_FOREACH(cpu) {
 813                 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu);
 814                 sched_bind(td, cpu);
 815                 epoch_call(epoch, &er->er_drain_ctx, &epoch_drain_cb);
 816         }
 817
 818         /* restore CPU binding, if any */
 819         if (was_bound != 0) {
 820                 sched_bind(td, old_cpu);
 821         } else {
 822                 /* get thread back to initial CPU, if any */
 823                 if (old_pinned != 0)
 824                         sched_bind(td, old_cpu);
 825                 sched_unbind(td);
 826         }
 827         /* restore pinned after bind */
 828         td->td_pinned = old_pinned;
 829
 830         thread_unlock(td);
 831
 832         while (epoch->e_drain_count != 0)
 833                 msleep(epoch, &epoch->e_drain_mtx, PZERO, "EDRAIN", 0);
 834
 835         mtx_unlock(&epoch->e_drain_mtx);
 836         sx_xunlock(&epoch->e_drain_sx);
 837
 838         PICKUP_GIANT();
 839 }