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 | CTLFLAG_MPSAFE, 0,
  96     "epoch information");
  97 SYSCTL_NODE(_kern_epoch, OID_AUTO, stats, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
  98     "epoch stats");
  99
 100 /* Stats. */
 101 static counter_u64_t block_count;
 102
 103 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, nblocked, CTLFLAG_RW,
 104     &block_count, "# of times a thread was in an epoch when epoch_wait was called");
 105 static counter_u64_t migrate_count;
 106
 107 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, migrations, CTLFLAG_RW,
 108     &migrate_count, "# of times thread was migrated to another CPU in epoch_wait");
 109 static counter_u64_t turnstile_count;
 110
 111 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, ncontended, CTLFLAG_RW,
 112     &turnstile_count, "# of times a thread was blocked on a lock in an epoch during an epoch_wait");
 113 static counter_u64_t switch_count;
 114
 115 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, switches, CTLFLAG_RW,
 116     &switch_count, "# of times a thread voluntarily context switched in epoch_wait");
 117 static counter_u64_t epoch_call_count;
 118
 119 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, epoch_calls, CTLFLAG_RW,
 120     &epoch_call_count, "# of times a callback was deferred");
 121 static counter_u64_t epoch_call_task_count;
 122
 123 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, epoch_call_tasks, CTLFLAG_RW,
 124     &epoch_call_task_count, "# of times a callback task was run");
 125
 126 TAILQ_HEAD (threadlist, thread);
 127
 128 CK_STACK_CONTAINER(struct ck_epoch_entry, stack_entry,
 129     ck_epoch_entry_container)
 130
 131 epoch_t allepochs[MAX_EPOCHS];
 132
 133 DPCPU_DEFINE(struct grouptask, epoch_cb_task);
 134 DPCPU_DEFINE(int, epoch_cb_count);
 135
 136 static __read_mostly int inited;
 137 static __read_mostly int epoch_count;
 138 __read_mostly epoch_t global_epoch;
 139 __read_mostly epoch_t global_epoch_preempt;
 140
 141 static void epoch_call_task(void *context __unused);
 142 static  uma_zone_t pcpu_zone_record;
 143
 144 #ifdef EPOCH_TRACE
 145 struct stackentry {
 146         RB_ENTRY(stackentry) se_node;
 147         struct stack se_stack;
 148 };
 149
 150 static int
 151 stackentry_compare(struct stackentry *a, struct stackentry *b)
 152 {
 153
 154         if (a->se_stack.depth > b->se_stack.depth)
 155                 return (1);
 156         if (a->se_stack.depth < b->se_stack.depth)
 157                 return (-1);
 158         for (int i = 0; i < a->se_stack.depth; i++) {
 159                 if (a->se_stack.pcs[i] > b->se_stack.pcs[i])
 160                         return (1);
 161                 if (a->se_stack.pcs[i] < b->se_stack.pcs[i])
 162                         return (-1);
 163         }
 164
 165         return (0);
 166 }
 167
 168 RB_HEAD(stacktree, stackentry) epoch_stacks = RB_INITIALIZER(&epoch_stacks);
 169 RB_GENERATE_STATIC(stacktree, stackentry, se_node, stackentry_compare);
 170
 171 static struct mtx epoch_stacks_lock;
 172 MTX_SYSINIT(epochstacks, &epoch_stacks_lock, "epoch_stacks", MTX_DEF);
 173
 174 static bool epoch_trace_stack_print = true;
 175 SYSCTL_BOOL(_kern_epoch, OID_AUTO, trace_stack_print, CTLFLAG_RWTUN,
 176     &epoch_trace_stack_print, 0, "Print stack traces on epoch reports");
 177
 178 static void epoch_trace_report(const char *fmt, ...) __printflike(1, 2);
 179 static inline void
 180 epoch_trace_report(const char *fmt, ...)
 181 {
 182         va_list ap;
 183         struct stackentry se, *new;
 184
 185         stack_zero(&se.se_stack);       /* XXX: is it really needed? */
 186         stack_save(&se.se_stack);
 187
 188         /* Tree is never reduced - go lockless. */
 189         if (RB_FIND(stacktree, &epoch_stacks, &se) != NULL)
 190                 return;
 191
 192         new = malloc(sizeof(*new), M_STACK, M_NOWAIT);
 193         if (new != NULL) {
 194                 bcopy(&se.se_stack, &new->se_stack, sizeof(struct stack));
 195
 196                 mtx_lock(&epoch_stacks_lock);
 197                 new = RB_INSERT(stacktree, &epoch_stacks, new);
 198                 mtx_unlock(&epoch_stacks_lock);
 199                 if (new != NULL)
 200                         free(new, M_STACK);
 201         }
 202
 203         va_start(ap, fmt);
 204         (void)vprintf(fmt, ap);
 205         va_end(ap);
 206         if (epoch_trace_stack_print)
 207                 stack_print_ddb(&se.se_stack);
 208 }
 209
 210 static inline void
 211 epoch_trace_enter(struct thread *td, epoch_t epoch, epoch_tracker_t et,
 212     const char *file, int line)
 213 {
 214         epoch_tracker_t iet;
 215
 216         SLIST_FOREACH(iet, &td->td_epochs, et_tlink)
 217                 if (iet->et_epoch == epoch)
 218                         epoch_trace_report("Recursively entering epoch %s "
 219                             "at %s:%d, previously entered at %s:%d\n",
 220                             epoch->e_name, file, line,
 221                             iet->et_file, iet->et_line);
 222         et->et_epoch = epoch;
 223         et->et_file = file;
 224         et->et_line = line;
 225         SLIST_INSERT_HEAD(&td->td_epochs, et, et_tlink);
 226 }
 227
 228 static inline void
 229 epoch_trace_exit(struct thread *td, epoch_t epoch, epoch_tracker_t et,
 230     const char *file, int line)
 231 {
 232
 233         if (SLIST_FIRST(&td->td_epochs) != et) {
 234                 epoch_trace_report("Exiting epoch %s in a not nested order "
 235                     "at %s:%d. Most recently entered %s at %s:%d\n",
 236                     epoch->e_name,
 237                     file, line,
 238                     SLIST_FIRST(&td->td_epochs)->et_epoch->e_name,
 239                     SLIST_FIRST(&td->td_epochs)->et_file,
 240                     SLIST_FIRST(&td->td_epochs)->et_line);
 241                 /* This will panic if et is not anywhere on td_epochs. */
 242                 SLIST_REMOVE(&td->td_epochs, et, epoch_tracker, et_tlink);
 243         } else
 244                 SLIST_REMOVE_HEAD(&td->td_epochs, et_tlink);
 245 }
 246
 247 /* Used by assertions that check thread state before going to sleep. */
 248 void
 249 epoch_trace_list(struct thread *td)
 250 {
 251         epoch_tracker_t iet;
 252
 253         SLIST_FOREACH(iet, &td->td_epochs, et_tlink)
 254                 printf("Epoch %s entered at %s:%d\n", iet->et_epoch->e_name,
 255                     iet->et_file, iet->et_line);
 256 }
 257 #endif /* EPOCH_TRACE */
 258
 259 static void
 260 epoch_init(void *arg __unused)
 261 {
 262         int cpu;
 263
 264         block_count = counter_u64_alloc(M_WAITOK);
 265         migrate_count = counter_u64_alloc(M_WAITOK);
 266         turnstile_count = counter_u64_alloc(M_WAITOK);
 267         switch_count = counter_u64_alloc(M_WAITOK);
 268         epoch_call_count = counter_u64_alloc(M_WAITOK);
 269         epoch_call_task_count = counter_u64_alloc(M_WAITOK);
 270
 271         pcpu_zone_record = uma_zcreate("epoch_record pcpu",
 272             sizeof(struct epoch_record), NULL, NULL, NULL, NULL,
 273             UMA_ALIGN_PTR, UMA_ZONE_PCPU);
 274         CPU_FOREACH(cpu) {
 275                 GROUPTASK_INIT(DPCPU_ID_PTR(cpu, epoch_cb_task), 0,
 276                     epoch_call_task, NULL);
 277                 taskqgroup_attach_cpu(qgroup_softirq,
 278                     DPCPU_ID_PTR(cpu, epoch_cb_task), NULL, cpu, NULL, NULL,
 279                     "epoch call task");
 280         }
 281 #ifdef EPOCH_TRACE
 282         SLIST_INIT(&thread0.td_epochs);
 283 #endif
 284         inited = 1;
 285         global_epoch = epoch_alloc("Global", 0);
 286         global_epoch_preempt = epoch_alloc("Global preemptible", EPOCH_PREEMPT);
 287 }
 288 SYSINIT(epoch, SI_SUB_EPOCH, SI_ORDER_FIRST, epoch_init, NULL);
 289
 290 #if !defined(EARLY_AP_STARTUP)
 291 static void
 292 epoch_init_smp(void *dummy __unused)
 293 {
 294         inited = 2;
 295 }
 296 SYSINIT(epoch_smp, SI_SUB_SMP + 1, SI_ORDER_FIRST, epoch_init_smp, NULL);
 297 #endif
 298
 299 static void
 300 epoch_ctor(epoch_t epoch)
 301 {
 302         epoch_record_t er;
 303         int cpu;
 304
 305         epoch->e_pcpu_record = uma_zalloc_pcpu(pcpu_zone_record, M_WAITOK);
 306         CPU_FOREACH(cpu) {
 307                 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu);
 308                 bzero(er, sizeof(*er));
 309                 ck_epoch_register(&epoch->e_epoch, &er->er_record, NULL);
 310                 TAILQ_INIT((struct threadlist *)(uintptr_t)&er->er_tdlist);
 311                 er->er_cpuid = cpu;
 312                 er->er_parent = epoch;
 313         }
 314 }
 315
 316 static void
 317 epoch_adjust_prio(struct thread *td, u_char prio)
 318 {
 319
 320         thread_lock(td);
 321         sched_prio(td, prio);
 322         thread_unlock(td);
 323 }
 324
 325 epoch_t
 326 epoch_alloc(const char *name, int flags)
 327 {
 328         epoch_t epoch;
 329
 330         if (__predict_false(!inited))
 331                 panic("%s called too early in boot", __func__);
 332         epoch = malloc(sizeof(struct epoch), M_EPOCH, M_ZERO | M_WAITOK);
 333         ck_epoch_init(&epoch->e_epoch);
 334         epoch_ctor(epoch);
 335         MPASS(epoch_count < MAX_EPOCHS - 2);
 336         epoch->e_flags = flags;
 337         epoch->e_idx = epoch_count;
 338         epoch->e_name = name;
 339         sx_init(&epoch->e_drain_sx, "epoch-drain-sx");
 340         mtx_init(&epoch->e_drain_mtx, "epoch-drain-mtx", NULL, MTX_DEF);
 341         allepochs[epoch_count++] = epoch;
 342         return (epoch);
 343 }
 344
 345 void
 346 epoch_free(epoch_t epoch)
 347 {
 348
 349         epoch_drain_callbacks(epoch);
 350         allepochs[epoch->e_idx] = NULL;
 351         epoch_wait(global_epoch);
 352         uma_zfree_pcpu(pcpu_zone_record, epoch->e_pcpu_record);
 353         mtx_destroy(&epoch->e_drain_mtx);
 354         sx_destroy(&epoch->e_drain_sx);
 355         free(epoch, M_EPOCH);
 356 }
 357
 358 static epoch_record_t
 359 epoch_currecord(epoch_t epoch)
 360 {
 361
 362         return (zpcpu_get(epoch->e_pcpu_record));
 363 }
 364
 365 #define INIT_CHECK(epoch)                                       \
 366         do {                                                    \
 367                 if (__predict_false((epoch) == NULL))           \
 368                         return;                                 \
 369         } while (0)
 370
 371 void
 372 _epoch_enter_preempt(epoch_t epoch, epoch_tracker_t et EPOCH_FILE_LINE)
 373 {
 374         struct epoch_record *er;
 375         struct thread *td;
 376
 377         MPASS(cold || epoch != NULL);
 378         MPASS(epoch->e_flags & EPOCH_PREEMPT);
 379         td = curthread;
 380         MPASS((vm_offset_t)et >= td->td_kstack &&
 381             (vm_offset_t)et + sizeof(struct epoch_tracker) <=
 382             td->td_kstack + td->td_kstack_pages * PAGE_SIZE);
 383
 384         INIT_CHECK(epoch);
 385 #ifdef EPOCH_TRACE
 386         epoch_trace_enter(td, epoch, et, file, line);
 387 #endif
 388         et->et_td = td;
 389         THREAD_NO_SLEEPING();
 390         critical_enter();
 391         sched_pin();
 392         td->td_pre_epoch_prio = td->td_priority;
 393         er = epoch_currecord(epoch);
 394         TAILQ_INSERT_TAIL(&er->er_tdlist, et, et_link);
 395         ck_epoch_begin(&er->er_record, &et->et_section);
 396         critical_exit();
 397 }
 398
 399 void
 400 epoch_enter(epoch_t epoch)
 401 {
 402         epoch_record_t er;
 403
 404         MPASS(cold || epoch != NULL);
 405         INIT_CHECK(epoch);
 406         critical_enter();
 407         er = epoch_currecord(epoch);
 408         ck_epoch_begin(&er->er_record, NULL);
 409 }
 410
 411 void
 412 _epoch_exit_preempt(epoch_t epoch, epoch_tracker_t et EPOCH_FILE_LINE)
 413 {
 414         struct epoch_record *er;
 415         struct thread *td;
 416
 417         INIT_CHECK(epoch);
 418         td = curthread;
 419         critical_enter();
 420         sched_unpin();
 421         THREAD_SLEEPING_OK();
 422         er = epoch_currecord(epoch);
 423         MPASS(epoch->e_flags & EPOCH_PREEMPT);
 424         MPASS(et != NULL);
 425         MPASS(et->et_td == td);
 426 #ifdef INVARIANTS
 427         et->et_td = (void*)0xDEADBEEF;
 428 #endif
 429         ck_epoch_end(&er->er_record, &et->et_section);
 430         TAILQ_REMOVE(&er->er_tdlist, et, et_link);
 431         er->er_gen++;
 432         if (__predict_false(td->td_pre_epoch_prio != td->td_priority))
 433                 epoch_adjust_prio(td, td->td_pre_epoch_prio);
 434         critical_exit();
 435 #ifdef EPOCH_TRACE
 436         epoch_trace_exit(td, epoch, et, file, line);
 437 #endif
 438 }
 439
 440 void
 441 epoch_exit(epoch_t epoch)
 442 {
 443         epoch_record_t er;
 444
 445         INIT_CHECK(epoch);
 446         er = epoch_currecord(epoch);
 447         ck_epoch_end(&er->er_record, NULL);
 448         critical_exit();
 449 }
 450
 451 /*
 452  * epoch_block_handler_preempt() is a callback from the CK code when another
 453  * thread is currently in an epoch section.
 454  */
 455 static void
 456 epoch_block_handler_preempt(struct ck_epoch *global __unused,
 457     ck_epoch_record_t *cr, void *arg __unused)
 458 {
 459         epoch_record_t record;
 460         struct thread *td, *owner, *curwaittd;
 461         struct epoch_tracker *tdwait;
 462         struct turnstile *ts;
 463         struct lock_object *lock;
 464         int spincount, gen;
 465         int locksheld __unused;
 466
 467         record = __containerof(cr, struct epoch_record, er_record);
 468         td = curthread;
 469         locksheld = td->td_locks;
 470         spincount = 0;
 471         counter_u64_add(block_count, 1);
 472         /*
 473          * We lost a race and there's no longer any threads
 474          * on the CPU in an epoch section.
 475          */
 476         if (TAILQ_EMPTY(&record->er_tdlist))
 477                 return;
 478
 479         if (record->er_cpuid != curcpu) {
 480                 /*
 481                  * If the head of the list is running, we can wait for it
 482                  * to remove itself from the list and thus save us the
 483                  * overhead of a migration
 484                  */
 485                 gen = record->er_gen;
 486                 thread_unlock(td);
 487                 /*
 488                  * We can't actually check if the waiting thread is running
 489                  * so we simply poll for it to exit before giving up and
 490                  * migrating.
 491                  */
 492                 do {
 493                         cpu_spinwait();
 494                 } while (!TAILQ_EMPTY(&record->er_tdlist) &&
 495                                  gen == record->er_gen &&
 496                                  spincount++ < MAX_ADAPTIVE_SPIN);
 497                 thread_lock(td);
 498                 /*
 499                  * If the generation has changed we can poll again
 500                  * otherwise we need to migrate.
 501                  */
 502                 if (gen != record->er_gen)
 503                         return;
 504                 /*
 505                  * Being on the same CPU as that of the record on which
 506                  * we need to wait allows us access to the thread
 507                  * list associated with that CPU. We can then examine the
 508                  * oldest thread in the queue and wait on its turnstile
 509                  * until it resumes and so on until a grace period
 510                  * elapses.
 511                  *
 512                  */
 513                 counter_u64_add(migrate_count, 1);
 514                 sched_bind(td, record->er_cpuid);
 515                 /*
 516                  * At this point we need to return to the ck code
 517                  * to scan to see if a grace period has elapsed.
 518                  * We can't move on to check the thread list, because
 519                  * in the meantime new threads may have arrived that
 520                  * in fact belong to a different epoch.
 521                  */
 522                 return;
 523         }
 524         /*
 525          * Try to find a thread in an epoch section on this CPU
 526          * waiting on a turnstile. Otherwise find the lowest
 527          * priority thread (highest prio value) and drop our priority
 528          * to match to allow it to run.
 529          */
 530         TAILQ_FOREACH(tdwait, &record->er_tdlist, et_link) {
 531                 /*
 532                  * Propagate our priority to any other waiters to prevent us
 533                  * from starving them. They will have their original priority
 534                  * restore on exit from epoch_wait().
 535                  */
 536                 curwaittd = tdwait->et_td;
 537                 if (!TD_IS_INHIBITED(curwaittd) && curwaittd->td_priority > td->td_priority) {
 538                         critical_enter();
 539                         thread_unlock(td);
 540                         thread_lock(curwaittd);
 541                         sched_prio(curwaittd, td->td_priority);
 542                         thread_unlock(curwaittd);
 543                         thread_lock(td);
 544                         critical_exit();
 545                 }
 546                 if (TD_IS_INHIBITED(curwaittd) && TD_ON_LOCK(curwaittd) &&
 547                     ((ts = curwaittd->td_blocked) != NULL)) {
 548                         /*
 549                          * We unlock td to allow turnstile_wait to reacquire
 550                          * the thread lock. Before unlocking it we enter a
 551                          * critical section to prevent preemption after we
 552                          * reenable interrupts by dropping the thread lock in
 553                          * order to prevent curwaittd from getting to run.
 554                          */
 555                         critical_enter();
 556                         thread_unlock(td);
 557
 558                         if (turnstile_lock(ts, &lock, &owner)) {
 559                                 if (ts == curwaittd->td_blocked) {
 560                                         MPASS(TD_IS_INHIBITED(curwaittd) &&
 561                                             TD_ON_LOCK(curwaittd));
 562                                         critical_exit();
 563                                         turnstile_wait(ts, owner,
 564                                             curwaittd->td_tsqueue);
 565                                         counter_u64_add(turnstile_count, 1);
 566                                         thread_lock(td);
 567                                         return;
 568                                 }
 569                                 turnstile_unlock(ts, lock);
 570                         }
 571                         thread_lock(td);
 572                         critical_exit();
 573                         KASSERT(td->td_locks == locksheld,
 574                             ("%d extra locks held", td->td_locks - locksheld));
 575                 }
 576         }
 577         /*
 578          * We didn't find any threads actually blocked on a lock
 579          * so we have nothing to do except context switch away.
 580          */
 581         counter_u64_add(switch_count, 1);
 582         mi_switch(SW_VOL | SWT_RELINQUISH);
 583         /*
 584          * It is important the thread lock is dropped while yielding
 585          * to allow other threads to acquire the lock pointed to by
 586          * TDQ_LOCKPTR(td). Currently mi_switch() will unlock the
 587          * thread lock before returning. Else a deadlock like
 588          * situation might happen.
 589          */
 590         thread_lock(td);
 591 }
 592
 593 void
 594 epoch_wait_preempt(epoch_t epoch)
 595 {
 596         struct thread *td;
 597         int was_bound;
 598         int old_cpu;
 599         int old_pinned;
 600         u_char old_prio;
 601         int locks __unused;
 602
 603         MPASS(cold || epoch != NULL);
 604         INIT_CHECK(epoch);
 605         td = curthread;
 606 #ifdef INVARIANTS
 607         locks = curthread->td_locks;
 608         MPASS(epoch->e_flags & EPOCH_PREEMPT);
 609         if ((epoch->e_flags & EPOCH_LOCKED) == 0)
 610                 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
 611                     "epoch_wait() can be long running");
 612         KASSERT(!in_epoch(epoch), ("epoch_wait_preempt() called in the middle "
 613             "of an epoch section of the same epoch"));
 614 #endif
 615         DROP_GIANT();
 616         thread_lock(td);
 617
 618         old_cpu = PCPU_GET(cpuid);
 619         old_pinned = td->td_pinned;
 620         old_prio = td->td_priority;
 621         was_bound = sched_is_bound(td);
 622         sched_unbind(td);
 623         td->td_pinned = 0;
 624         sched_bind(td, old_cpu);
 625
 626         ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler_preempt,
 627             NULL);
 628
 629         /* restore CPU binding, if any */
 630         if (was_bound != 0) {
 631                 sched_bind(td, old_cpu);
 632         } else {
 633                 /* get thread back to initial CPU, if any */
 634                 if (old_pinned != 0)
 635                         sched_bind(td, old_cpu);
 636                 sched_unbind(td);
 637         }
 638         /* restore pinned after bind */
 639         td->td_pinned = old_pinned;
 640
 641         /* restore thread priority */
 642         sched_prio(td, old_prio);
 643         thread_unlock(td);
 644         PICKUP_GIANT();
 645         KASSERT(td->td_locks == locks,
 646             ("%d residual locks held", td->td_locks - locks));
 647 }
 648
 649 static void
 650 epoch_block_handler(struct ck_epoch *g __unused, ck_epoch_record_t *c __unused,
 651     void *arg __unused)
 652 {
 653         cpu_spinwait();
 654 }
 655
 656 void
 657 epoch_wait(epoch_t epoch)
 658 {
 659
 660         MPASS(cold || epoch != NULL);
 661         INIT_CHECK(epoch);
 662         MPASS(epoch->e_flags == 0);
 663         critical_enter();
 664         ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler, NULL);
 665         critical_exit();
 666 }
 667
 668 void
 669 epoch_call(epoch_t epoch, epoch_callback_t callback, epoch_context_t ctx)
 670 {
 671         epoch_record_t er;
 672         ck_epoch_entry_t *cb;
 673
 674         cb = (void *)ctx;
 675
 676         MPASS(callback);
 677         /* too early in boot to have epoch set up */
 678         if (__predict_false(epoch == NULL))
 679                 goto boottime;
 680 #if !defined(EARLY_AP_STARTUP)
 681         if (__predict_false(inited < 2))
 682                 goto boottime;
 683 #endif
 684
 685         critical_enter();
 686         *DPCPU_PTR(epoch_cb_count) += 1;
 687         er = epoch_currecord(epoch);
 688         ck_epoch_call(&er->er_record, cb, (ck_epoch_cb_t *)callback);
 689         critical_exit();
 690         return;
 691 boottime:
 692         callback(ctx);
 693 }
 694
 695 static void
 696 epoch_call_task(void *arg __unused)
 697 {
 698         ck_stack_entry_t *cursor, *head, *next;
 699         ck_epoch_record_t *record;
 700         epoch_record_t er;
 701         epoch_t epoch;
 702         ck_stack_t cb_stack;
 703         int i, npending, total;
 704
 705         ck_stack_init(&cb_stack);
 706         critical_enter();
 707         epoch_enter(global_epoch);
 708         for (total = i = 0; i < epoch_count; i++) {
 709                 if (__predict_false((epoch = allepochs[i]) == NULL))
 710                         continue;
 711                 er = epoch_currecord(epoch);
 712                 record = &er->er_record;
 713                 if ((npending = record->n_pending) == 0)
 714                         continue;
 715                 ck_epoch_poll_deferred(record, &cb_stack);
 716                 total += npending - record->n_pending;
 717         }
 718         epoch_exit(global_epoch);
 719         *DPCPU_PTR(epoch_cb_count) -= total;
 720         critical_exit();
 721
 722         counter_u64_add(epoch_call_count, total);
 723         counter_u64_add(epoch_call_task_count, 1);
 724
 725         head = ck_stack_batch_pop_npsc(&cb_stack);
 726         for (cursor = head; cursor != NULL; cursor = next) {
 727                 struct ck_epoch_entry *entry =
 728                     ck_epoch_entry_container(cursor);
 729
 730                 next = CK_STACK_NEXT(cursor);
 731                 entry->function(entry);
 732         }
 733 }
 734
 735 int
 736 in_epoch_verbose(epoch_t epoch, int dump_onfail)
 737 {
 738         struct epoch_tracker *tdwait;
 739         struct thread *td;
 740         epoch_record_t er;
 741
 742         td = curthread;
 743         if (THREAD_CAN_SLEEP())
 744                 return (0);
 745         if (__predict_false((epoch) == NULL))
 746                 return (0);
 747         critical_enter();
 748         er = epoch_currecord(epoch);
 749         TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link)
 750                 if (tdwait->et_td == td) {
 751                         critical_exit();
 752                         return (1);
 753                 }
 754 #ifdef INVARIANTS
 755         if (dump_onfail) {
 756                 MPASS(td->td_pinned);
 757                 printf("cpu: %d id: %d\n", curcpu, td->td_tid);
 758                 TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link)
 759                         printf("td_tid: %d ", tdwait->et_td->td_tid);
 760                 printf("\n");
 761         }
 762 #endif
 763         critical_exit();
 764         return (0);
 765 }
 766
 767 int
 768 in_epoch(epoch_t epoch)
 769 {
 770         return (in_epoch_verbose(epoch, 0));
 771 }
 772
 773 static void
 774 epoch_drain_cb(struct epoch_context *ctx)
 775 {
 776         struct epoch *epoch =
 777             __containerof(ctx, struct epoch_record, er_drain_ctx)->er_parent;
 778
 779         if (atomic_fetchadd_int(&epoch->e_drain_count, -1) == 1) {
 780                 mtx_lock(&epoch->e_drain_mtx);
 781                 wakeup(epoch);
 782                 mtx_unlock(&epoch->e_drain_mtx);
 783         }
 784 }
 785
 786 void
 787 epoch_drain_callbacks(epoch_t epoch)
 788 {
 789         epoch_record_t er;
 790         struct thread *td;
 791         int was_bound;
 792         int old_pinned;
 793         int old_cpu;
 794         int cpu;
 795
 796         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
 797             "epoch_drain_callbacks() may sleep!");
 798
 799         /* too early in boot to have epoch set up */
 800         if (__predict_false(epoch == NULL))
 801                 return;
 802 #if !defined(EARLY_AP_STARTUP)
 803         if (__predict_false(inited < 2))
 804                 return;
 805 #endif
 806         DROP_GIANT();
 807
 808         sx_xlock(&epoch->e_drain_sx);
 809         mtx_lock(&epoch->e_drain_mtx);
 810
 811         td = curthread;
 812         thread_lock(td);
 813         old_cpu = PCPU_GET(cpuid);
 814         old_pinned = td->td_pinned;
 815         was_bound = sched_is_bound(td);
 816         sched_unbind(td);
 817         td->td_pinned = 0;
 818
 819         CPU_FOREACH(cpu)
 820                 epoch->e_drain_count++;
 821         CPU_FOREACH(cpu) {
 822                 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu);
 823                 sched_bind(td, cpu);
 824                 epoch_call(epoch, &epoch_drain_cb, &er->er_drain_ctx);
 825         }
 826
 827         /* restore CPU binding, if any */
 828         if (was_bound != 0) {
 829                 sched_bind(td, old_cpu);
 830         } else {
 831                 /* get thread back to initial CPU, if any */
 832                 if (old_pinned != 0)
 833                         sched_bind(td, old_cpu);
 834                 sched_unbind(td);
 835         }
 836         /* restore pinned after bind */
 837         td->td_pinned = old_pinned;
 838
 839         thread_unlock(td);
 840
 841         while (epoch->e_drain_count != 0)
 842                 msleep(epoch, &epoch->e_drain_mtx, PZERO, "EDRAIN", 0);
 843
 844         mtx_unlock(&epoch->e_drain_mtx);
 845         sx_xunlock(&epoch->e_drain_sx);
 846
 847         PICKUP_GIANT();
 848 }