sys/kern/subr_epoch.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
   3  *
   4  * Copyright (c) 2018, Matthew Macy <mmacy@freebsd.org>
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, this list of conditions and the following disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  *
  15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  16  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  17  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  18  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  19  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  20  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  21  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  22  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  23  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  24  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  25  * SUCH DAMAGE.
  26  *
  27  */
  28
  29 #include <sys/cdefs.h>
  30 __FBSDID("$FreeBSD$");
  31
  32 #include <sys/param.h>
  33 #include <sys/systm.h>
  34 #include <sys/counter.h>
  35 #include <sys/epoch.h>
  36 #include <sys/gtaskqueue.h>
  37 #include <sys/kernel.h>
  38 #include <sys/limits.h>
  39 #include <sys/lock.h>
  40 #include <sys/malloc.h>
  41 #include <sys/mutex.h>
  42 #include <sys/pcpu.h>
  43 #include <sys/proc.h>
  44 #include <sys/sched.h>
  45 #include <sys/sx.h>
  46 #include <sys/smp.h>
  47 #include <sys/sysctl.h>
  48 #include <sys/turnstile.h>
  49 #ifdef EPOCH_TRACE
  50 #include <machine/stdarg.h>
  51 #include <sys/stack.h>
  52 #include <sys/tree.h>
  53 #endif
  54 #include <vm/vm.h>
  55 #include <vm/vm_extern.h>
  56 #include <vm/vm_kern.h>
  57 #include <vm/uma.h>
  58
  59 #include <ck_epoch.h>
  60
  61 #ifdef __amd64__
  62 #define EPOCH_ALIGN CACHE_LINE_SIZE*2
  63 #else
  64 #define EPOCH_ALIGN CACHE_LINE_SIZE
  65 #endif
  66
  67 TAILQ_HEAD (epoch_tdlist, epoch_tracker);
  68 typedef struct epoch_record {
  69         ck_epoch_record_t er_record;
  70         struct epoch_context er_drain_ctx;
  71         struct epoch *er_parent;
  72         volatile struct epoch_tdlist er_tdlist;
  73         volatile uint32_t er_gen;
  74         uint32_t er_cpuid;
  75 #ifdef INVARIANTS
  76         /* Used to verify record ownership for non-preemptible epochs. */
  77         struct thread *er_td;
  78 #endif
  79 } __aligned(EPOCH_ALIGN)     *epoch_record_t;
  80
  81 struct epoch {
  82         struct ck_epoch e_epoch __aligned(EPOCH_ALIGN);
  83         epoch_record_t e_pcpu_record;
  84         int     e_in_use;
  85         int     e_flags;
  86         struct sx e_drain_sx;
  87         struct mtx e_drain_mtx;
  88         volatile int e_drain_count;
  89         const char *e_name;
  90 };
  91
  92 /* arbitrary --- needs benchmarking */
  93 #define MAX_ADAPTIVE_SPIN 100
  94 #define MAX_EPOCHS 64
  95
  96 CTASSERT(sizeof(ck_epoch_entry_t) == sizeof(struct epoch_context));
  97 SYSCTL_NODE(_kern, OID_AUTO, epoch, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
  98     "epoch information");
  99 SYSCTL_NODE(_kern_epoch, OID_AUTO, stats, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
 100     "epoch stats");
 101
 102 /* Stats. */
 103 static counter_u64_t block_count;
 104
 105 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, nblocked, CTLFLAG_RW,
 106     &block_count, "# of times a thread was in an epoch when epoch_wait was called");
 107 static counter_u64_t migrate_count;
 108
 109 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, migrations, CTLFLAG_RW,
 110     &migrate_count, "# of times thread was migrated to another CPU in epoch_wait");
 111 static counter_u64_t turnstile_count;
 112
 113 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, ncontended, CTLFLAG_RW,
 114     &turnstile_count, "# of times a thread was blocked on a lock in an epoch during an epoch_wait");
 115 static counter_u64_t switch_count;
 116
 117 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, switches, CTLFLAG_RW,
 118     &switch_count, "# of times a thread voluntarily context switched in epoch_wait");
 119 static counter_u64_t epoch_call_count;
 120
 121 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, epoch_calls, CTLFLAG_RW,
 122     &epoch_call_count, "# of times a callback was deferred");
 123 static counter_u64_t epoch_call_task_count;
 124
 125 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, epoch_call_tasks, CTLFLAG_RW,
 126     &epoch_call_task_count, "# of times a callback task was run");
 127
 128 TAILQ_HEAD (threadlist, thread);
 129
 130 CK_STACK_CONTAINER(struct ck_epoch_entry, stack_entry,
 131     ck_epoch_entry_container)
 132
 133 static struct epoch epoch_array[MAX_EPOCHS];
 134
 135 DPCPU_DEFINE(struct grouptask, epoch_cb_task);
 136 DPCPU_DEFINE(int, epoch_cb_count);
 137
 138 static __read_mostly int inited;
 139 __read_mostly epoch_t global_epoch;
 140 __read_mostly epoch_t global_epoch_preempt;
 141
 142 static void epoch_call_task(void *context __unused);
 143 static  uma_zone_t pcpu_zone_record;
 144
 145 static struct sx epoch_sx;
 146
 147 #define EPOCH_LOCK() sx_xlock(&epoch_sx)
 148 #define EPOCH_UNLOCK() sx_xunlock(&epoch_sx)
 149
 150 static epoch_record_t
 151 epoch_currecord(epoch_t epoch)
 152 {
 153
 154         return (zpcpu_get(epoch->e_pcpu_record));
 155 }
 156
 157 #ifdef EPOCH_TRACE
 158 struct stackentry {
 159         RB_ENTRY(stackentry) se_node;
 160         struct stack se_stack;
 161 };
 162
 163 static int
 164 stackentry_compare(struct stackentry *a, struct stackentry *b)
 165 {
 166
 167         if (a->se_stack.depth > b->se_stack.depth)
 168                 return (1);
 169         if (a->se_stack.depth < b->se_stack.depth)
 170                 return (-1);
 171         for (int i = 0; i < a->se_stack.depth; i++) {
 172                 if (a->se_stack.pcs[i] > b->se_stack.pcs[i])
 173                         return (1);
 174                 if (a->se_stack.pcs[i] < b->se_stack.pcs[i])
 175                         return (-1);
 176         }
 177
 178         return (0);
 179 }
 180
 181 RB_HEAD(stacktree, stackentry) epoch_stacks = RB_INITIALIZER(&epoch_stacks);
 182 RB_GENERATE_STATIC(stacktree, stackentry, se_node, stackentry_compare);
 183
 184 static struct mtx epoch_stacks_lock;
 185 MTX_SYSINIT(epochstacks, &epoch_stacks_lock, "epoch_stacks", MTX_DEF);
 186
 187 static bool epoch_trace_stack_print = true;
 188 SYSCTL_BOOL(_kern_epoch, OID_AUTO, trace_stack_print, CTLFLAG_RWTUN,
 189     &epoch_trace_stack_print, 0, "Print stack traces on epoch reports");
 190
 191 static void epoch_trace_report(const char *fmt, ...) __printflike(1, 2);
 192 static inline void
 193 epoch_trace_report(const char *fmt, ...)
 194 {
 195         va_list ap;
 196         struct stackentry se, *new;
 197
 198         stack_zero(&se.se_stack);       /* XXX: is it really needed? */
 199         stack_save(&se.se_stack);
 200
 201         /* Tree is never reduced - go lockless. */
 202         if (RB_FIND(stacktree, &epoch_stacks, &se) != NULL)
 203                 return;
 204
 205         new = malloc(sizeof(*new), M_STACK, M_NOWAIT);
 206         if (new != NULL) {
 207                 bcopy(&se.se_stack, &new->se_stack, sizeof(struct stack));
 208
 209                 mtx_lock(&epoch_stacks_lock);
 210                 new = RB_INSERT(stacktree, &epoch_stacks, new);
 211                 mtx_unlock(&epoch_stacks_lock);
 212                 if (new != NULL)
 213                         free(new, M_STACK);
 214         }
 215
 216         va_start(ap, fmt);
 217         (void)vprintf(fmt, ap);
 218         va_end(ap);
 219         if (epoch_trace_stack_print)
 220                 stack_print_ddb(&se.se_stack);
 221 }
 222
 223 static inline void
 224 epoch_trace_enter(struct thread *td, epoch_t epoch, epoch_tracker_t et,
 225     const char *file, int line)
 226 {
 227         epoch_tracker_t iet;
 228
 229         SLIST_FOREACH(iet, &td->td_epochs, et_tlink) {
 230                 if (iet->et_epoch != epoch)
 231                         continue;
 232                 epoch_trace_report("Recursively entering epoch %s "
 233                     "at %s:%d, previously entered at %s:%d\n",
 234                     epoch->e_name, file, line,
 235                     iet->et_file, iet->et_line);
 236         }
 237         et->et_epoch = epoch;
 238         et->et_file = file;
 239         et->et_line = line;
 240         et->et_flags = 0;
 241         SLIST_INSERT_HEAD(&td->td_epochs, et, et_tlink);
 242 }
 243
 244 static inline void
 245 epoch_trace_exit(struct thread *td, epoch_t epoch, epoch_tracker_t et,
 246     const char *file, int line)
 247 {
 248
 249         if (SLIST_FIRST(&td->td_epochs) != et) {
 250                 epoch_trace_report("Exiting epoch %s in a not nested order "
 251                     "at %s:%d. Most recently entered %s at %s:%d\n",
 252                     epoch->e_name,
 253                     file, line,
 254                     SLIST_FIRST(&td->td_epochs)->et_epoch->e_name,
 255                     SLIST_FIRST(&td->td_epochs)->et_file,
 256                     SLIST_FIRST(&td->td_epochs)->et_line);
 257                 /* This will panic if et is not anywhere on td_epochs. */
 258                 SLIST_REMOVE(&td->td_epochs, et, epoch_tracker, et_tlink);
 259         } else
 260                 SLIST_REMOVE_HEAD(&td->td_epochs, et_tlink);
 261         if (et->et_flags & ET_REPORT_EXIT)
 262                 printf("Td %p exiting epoch %s at %s:%d\n", td, epoch->e_name,
 263                     file, line);
 264 }
 265
 266 /* Used by assertions that check thread state before going to sleep. */
 267 void
 268 epoch_trace_list(struct thread *td)
 269 {
 270         epoch_tracker_t iet;
 271
 272         SLIST_FOREACH(iet, &td->td_epochs, et_tlink)
 273                 printf("Epoch %s entered at %s:%d\n", iet->et_epoch->e_name,
 274                     iet->et_file, iet->et_line);
 275 }
 276
 277 void
 278 epoch_where_report(epoch_t epoch)
 279 {
 280         epoch_record_t er;
 281         struct epoch_tracker *tdwait;
 282
 283         MPASS(epoch != NULL);
 284         MPASS((epoch->e_flags & EPOCH_PREEMPT) != 0);
 285         MPASS(!THREAD_CAN_SLEEP());
 286         critical_enter();
 287         er = epoch_currecord(epoch);
 288         TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link)
 289                 if (tdwait->et_td == curthread)
 290                         break;
 291         critical_exit();
 292         if (tdwait != NULL) {
 293                 tdwait->et_flags |= ET_REPORT_EXIT;
 294                 printf("Td %p entered epoch %s at %s:%d\n", curthread,
 295                     epoch->e_name, tdwait->et_file, tdwait->et_line);
 296         }
 297 }
 298 #endif /* EPOCH_TRACE */
 299
 300 static void
 301 epoch_init(void *arg __unused)
 302 {
 303         int cpu;
 304
 305         block_count = counter_u64_alloc(M_WAITOK);
 306         migrate_count = counter_u64_alloc(M_WAITOK);
 307         turnstile_count = counter_u64_alloc(M_WAITOK);
 308         switch_count = counter_u64_alloc(M_WAITOK);
 309         epoch_call_count = counter_u64_alloc(M_WAITOK);
 310         epoch_call_task_count = counter_u64_alloc(M_WAITOK);
 311
 312         pcpu_zone_record = uma_zcreate("epoch_record pcpu",
 313             sizeof(struct epoch_record), NULL, NULL, NULL, NULL,
 314             UMA_ALIGN_PTR, UMA_ZONE_PCPU);
 315         CPU_FOREACH(cpu) {
 316                 GROUPTASK_INIT(DPCPU_ID_PTR(cpu, epoch_cb_task), 0,
 317                     epoch_call_task, NULL);
 318                 taskqgroup_attach_cpu(qgroup_softirq,
 319                     DPCPU_ID_PTR(cpu, epoch_cb_task), NULL, cpu, NULL, NULL,
 320                     "epoch call task");
 321         }
 322 #ifdef EPOCH_TRACE
 323         SLIST_INIT(&thread0.td_epochs);
 324 #endif
 325         sx_init(&epoch_sx, "epoch-sx");
 326         inited = 1;
 327         global_epoch = epoch_alloc("Global", 0);
 328         global_epoch_preempt = epoch_alloc("Global preemptible", EPOCH_PREEMPT);
 329 }
 330 SYSINIT(epoch, SI_SUB_EPOCH, SI_ORDER_FIRST, epoch_init, NULL);
 331
 332 #if !defined(EARLY_AP_STARTUP)
 333 static void
 334 epoch_init_smp(void *dummy __unused)
 335 {
 336         inited = 2;
 337 }
 338 SYSINIT(epoch_smp, SI_SUB_SMP + 1, SI_ORDER_FIRST, epoch_init_smp, NULL);
 339 #endif
 340
 341 static void
 342 epoch_ctor(epoch_t epoch)
 343 {
 344         epoch_record_t er;
 345         int cpu;
 346
 347         epoch->e_pcpu_record = uma_zalloc_pcpu(pcpu_zone_record, M_WAITOK);
 348         CPU_FOREACH(cpu) {
 349                 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu);
 350                 bzero(er, sizeof(*er));
 351                 ck_epoch_register(&epoch->e_epoch, &er->er_record, NULL);
 352                 TAILQ_INIT((struct threadlist *)(uintptr_t)&er->er_tdlist);
 353                 er->er_cpuid = cpu;
 354                 er->er_parent = epoch;
 355         }
 356 }
 357
 358 static void
 359 epoch_adjust_prio(struct thread *td, u_char prio)
 360 {
 361
 362         thread_lock(td);
 363         sched_prio(td, prio);
 364         thread_unlock(td);
 365 }
 366
 367 epoch_t
 368 epoch_alloc(const char *name, int flags)
 369 {
 370         epoch_t epoch;
 371         int i;
 372
 373         MPASS(name != NULL);
 374
 375         if (__predict_false(!inited))
 376                 panic("%s called too early in boot", __func__);
 377
 378         EPOCH_LOCK();
 379
 380         /*
 381          * Find a free index in the epoch array. If no free index is
 382          * found, try to use the index after the last one.
 383          */
 384         for (i = 0;; i++) {
 385                 /*
 386                  * If too many epochs are currently allocated,
 387                  * return NULL.
 388                  */
 389                 if (i == MAX_EPOCHS) {
 390                         epoch = NULL;
 391                         goto done;
 392                 }
 393                 if (epoch_array[i].e_in_use == 0)
 394                         break;
 395         }
 396
 397         epoch = epoch_array + i;
 398         ck_epoch_init(&epoch->e_epoch);
 399         epoch_ctor(epoch);
 400         epoch->e_flags = flags;
 401         epoch->e_name = name;
 402         sx_init(&epoch->e_drain_sx, "epoch-drain-sx");
 403         mtx_init(&epoch->e_drain_mtx, "epoch-drain-mtx", NULL, MTX_DEF);
 404
 405         /*
 406          * Set e_in_use last, because when this field is set the
 407          * epoch_call_task() function will start scanning this epoch
 408          * structure.
 409          */
 410         atomic_store_rel_int(&epoch->e_in_use, 1);
 411 done:
 412         EPOCH_UNLOCK();
 413         return (epoch);
 414 }
 415
 416 void
 417 epoch_free(epoch_t epoch)
 418 {
 419 #ifdef INVARIANTS
 420         int cpu;
 421 #endif
 422
 423         EPOCH_LOCK();
 424
 425         MPASS(epoch->e_in_use != 0);
 426
 427         epoch_drain_callbacks(epoch);
 428
 429         atomic_store_rel_int(&epoch->e_in_use, 0);
 430         /*
 431          * Make sure the epoch_call_task() function see e_in_use equal
 432          * to zero, by calling epoch_wait() on the global_epoch:
 433          */
 434         epoch_wait(global_epoch);
 435 #ifdef INVARIANTS
 436         CPU_FOREACH(cpu) {
 437                 epoch_record_t er;
 438
 439                 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu);
 440
 441                 /*
 442                  * Sanity check: none of the records should be in use anymore.
 443                  * We drained callbacks above and freeing the pcpu records is
 444                  * imminent.
 445                  */
 446                 MPASS(er->er_td == NULL);
 447                 MPASS(TAILQ_EMPTY(&er->er_tdlist));
 448         }
 449 #endif
 450         uma_zfree_pcpu(pcpu_zone_record, epoch->e_pcpu_record);
 451         mtx_destroy(&epoch->e_drain_mtx);
 452         sx_destroy(&epoch->e_drain_sx);
 453         memset(epoch, 0, sizeof(*epoch));
 454
 455         EPOCH_UNLOCK();
 456 }
 457
 458 #define INIT_CHECK(epoch)                                       \
 459         do {                                                    \
 460                 if (__predict_false((epoch) == NULL))           \
 461                         return;                                 \
 462         } while (0)
 463
 464 void
 465 _epoch_enter_preempt(epoch_t epoch, epoch_tracker_t et EPOCH_FILE_LINE)
 466 {
 467         struct epoch_record *er;
 468         struct thread *td;
 469
 470         MPASS(cold || epoch != NULL);
 471         td = curthread;
 472         MPASS((vm_offset_t)et >= td->td_kstack &&
 473             (vm_offset_t)et + sizeof(struct epoch_tracker) <=
 474             td->td_kstack + td->td_kstack_pages * PAGE_SIZE);
 475
 476         INIT_CHECK(epoch);
 477         MPASS(epoch->e_flags & EPOCH_PREEMPT);
 478
 479 #ifdef EPOCH_TRACE
 480         epoch_trace_enter(td, epoch, et, file, line);
 481 #endif
 482         et->et_td = td;
 483         THREAD_NO_SLEEPING();
 484         critical_enter();
 485         sched_pin();
 486         et->et_old_priority = td->td_priority;
 487         er = epoch_currecord(epoch);
 488         /* Record-level tracking is reserved for non-preemptible epochs. */
 489         MPASS(er->er_td == NULL);
 490         TAILQ_INSERT_TAIL(&er->er_tdlist, et, et_link);
 491         ck_epoch_begin(&er->er_record, &et->et_section);
 492         critical_exit();
 493 }
 494
 495 void
 496 epoch_enter(epoch_t epoch)
 497 {
 498         epoch_record_t er;
 499
 500         MPASS(cold || epoch != NULL);
 501         INIT_CHECK(epoch);
 502         critical_enter();
 503         er = epoch_currecord(epoch);
 504 #ifdef INVARIANTS
 505         if (er->er_record.active == 0) {
 506                 MPASS(er->er_td == NULL);
 507                 er->er_td = curthread;
 508         } else {
 509                 /* We've recursed, just make sure our accounting isn't wrong. */
 510                 MPASS(er->er_td == curthread);
 511         }
 512 #endif
 513         ck_epoch_begin(&er->er_record, NULL);
 514 }
 515
 516 void
 517 _epoch_exit_preempt(epoch_t epoch, epoch_tracker_t et EPOCH_FILE_LINE)
 518 {
 519         struct epoch_record *er;
 520         struct thread *td;
 521
 522         INIT_CHECK(epoch);
 523         td = curthread;
 524         critical_enter();
 525         sched_unpin();
 526         THREAD_SLEEPING_OK();
 527         er = epoch_currecord(epoch);
 528         MPASS(epoch->e_flags & EPOCH_PREEMPT);
 529         MPASS(et != NULL);
 530         MPASS(et->et_td == td);
 531 #ifdef INVARIANTS
 532         et->et_td = (void*)0xDEADBEEF;
 533         /* Record-level tracking is reserved for non-preemptible epochs. */
 534         MPASS(er->er_td == NULL);
 535 #endif
 536         ck_epoch_end(&er->er_record, &et->et_section);
 537         TAILQ_REMOVE(&er->er_tdlist, et, et_link);
 538         er->er_gen++;
 539         if (__predict_false(et->et_old_priority != td->td_priority))
 540                 epoch_adjust_prio(td, et->et_old_priority);
 541         critical_exit();
 542 #ifdef EPOCH_TRACE
 543         epoch_trace_exit(td, epoch, et, file, line);
 544 #endif
 545 }
 546
 547 void
 548 epoch_exit(epoch_t epoch)
 549 {
 550         epoch_record_t er;
 551
 552         INIT_CHECK(epoch);
 553         er = epoch_currecord(epoch);
 554         ck_epoch_end(&er->er_record, NULL);
 555 #ifdef INVARIANTS
 556         MPASS(er->er_td == curthread);
 557         if (er->er_record.active == 0)
 558                 er->er_td = NULL;
 559 #endif
 560         critical_exit();
 561 }
 562
 563 /*
 564  * epoch_block_handler_preempt() is a callback from the CK code when another
 565  * thread is currently in an epoch section.
 566  */
 567 static void
 568 epoch_block_handler_preempt(struct ck_epoch *global __unused,
 569     ck_epoch_record_t *cr, void *arg __unused)
 570 {
 571         epoch_record_t record;
 572         struct thread *td, *owner, *curwaittd;
 573         struct epoch_tracker *tdwait;
 574         struct turnstile *ts;
 575         struct lock_object *lock;
 576         int spincount, gen;
 577         int locksheld __unused;
 578
 579         record = __containerof(cr, struct epoch_record, er_record);
 580         td = curthread;
 581         locksheld = td->td_locks;
 582         spincount = 0;
 583         counter_u64_add(block_count, 1);
 584         /*
 585          * We lost a race and there's no longer any threads
 586          * on the CPU in an epoch section.
 587          */
 588         if (TAILQ_EMPTY(&record->er_tdlist))
 589                 return;
 590
 591         if (record->er_cpuid != curcpu) {
 592                 /*
 593                  * If the head of the list is running, we can wait for it
 594                  * to remove itself from the list and thus save us the
 595                  * overhead of a migration
 596                  */
 597                 gen = record->er_gen;
 598                 thread_unlock(td);
 599                 /*
 600                  * We can't actually check if the waiting thread is running
 601                  * so we simply poll for it to exit before giving up and
 602                  * migrating.
 603                  */
 604                 do {
 605                         cpu_spinwait();
 606                 } while (!TAILQ_EMPTY(&record->er_tdlist) &&
 607                                  gen == record->er_gen &&
 608                                  spincount++ < MAX_ADAPTIVE_SPIN);
 609                 thread_lock(td);
 610                 /*
 611                  * If the generation has changed we can poll again
 612                  * otherwise we need to migrate.
 613                  */
 614                 if (gen != record->er_gen)
 615                         return;
 616                 /*
 617                  * Being on the same CPU as that of the record on which
 618                  * we need to wait allows us access to the thread
 619                  * list associated with that CPU. We can then examine the
 620                  * oldest thread in the queue and wait on its turnstile
 621                  * until it resumes and so on until a grace period
 622                  * elapses.
 623                  *
 624                  */
 625                 counter_u64_add(migrate_count, 1);
 626                 sched_bind(td, record->er_cpuid);
 627                 /*
 628                  * At this point we need to return to the ck code
 629                  * to scan to see if a grace period has elapsed.
 630                  * We can't move on to check the thread list, because
 631                  * in the meantime new threads may have arrived that
 632                  * in fact belong to a different epoch.
 633                  */
 634                 return;
 635         }
 636         /*
 637          * Try to find a thread in an epoch section on this CPU
 638          * waiting on a turnstile. Otherwise find the lowest
 639          * priority thread (highest prio value) and drop our priority
 640          * to match to allow it to run.
 641          */
 642         TAILQ_FOREACH(tdwait, &record->er_tdlist, et_link) {
 643                 /*
 644                  * Propagate our priority to any other waiters to prevent us
 645                  * from starving them. They will have their original priority
 646                  * restore on exit from epoch_wait().
 647                  */
 648                 curwaittd = tdwait->et_td;
 649                 if (!TD_IS_INHIBITED(curwaittd) && curwaittd->td_priority > td->td_priority) {
 650                         critical_enter();
 651                         thread_unlock(td);
 652                         thread_lock(curwaittd);
 653                         sched_prio(curwaittd, td->td_priority);
 654                         thread_unlock(curwaittd);
 655                         thread_lock(td);
 656                         critical_exit();
 657                 }
 658                 if (TD_IS_INHIBITED(curwaittd) && TD_ON_LOCK(curwaittd) &&
 659                     ((ts = curwaittd->td_blocked) != NULL)) {
 660                         /*
 661                          * We unlock td to allow turnstile_wait to reacquire
 662                          * the thread lock. Before unlocking it we enter a
 663                          * critical section to prevent preemption after we
 664                          * reenable interrupts by dropping the thread lock in
 665                          * order to prevent curwaittd from getting to run.
 666                          */
 667                         critical_enter();
 668                         thread_unlock(td);
 669
 670                         if (turnstile_lock(ts, &lock, &owner)) {
 671                                 if (ts == curwaittd->td_blocked) {
 672                                         MPASS(TD_IS_INHIBITED(curwaittd) &&
 673                                             TD_ON_LOCK(curwaittd));
 674                                         critical_exit();
 675                                         turnstile_wait(ts, owner,
 676                                             curwaittd->td_tsqueue);
 677                                         counter_u64_add(turnstile_count, 1);
 678                                         thread_lock(td);
 679                                         return;
 680                                 }
 681                                 turnstile_unlock(ts, lock);
 682                         }
 683                         thread_lock(td);
 684                         critical_exit();
 685                         KASSERT(td->td_locks == locksheld,
 686                             ("%d extra locks held", td->td_locks - locksheld));
 687                 }
 688         }
 689         /*
 690          * We didn't find any threads actually blocked on a lock
 691          * so we have nothing to do except context switch away.
 692          */
 693         counter_u64_add(switch_count, 1);
 694         mi_switch(SW_VOL | SWT_RELINQUISH);
 695         /*
 696          * It is important the thread lock is dropped while yielding
 697          * to allow other threads to acquire the lock pointed to by
 698          * TDQ_LOCKPTR(td). Currently mi_switch() will unlock the
 699          * thread lock before returning. Else a deadlock like
 700          * situation might happen.
 701          */
 702         thread_lock(td);
 703 }
 704
 705 void
 706 epoch_wait_preempt(epoch_t epoch)
 707 {
 708         struct thread *td;
 709         int was_bound;
 710         int old_cpu;
 711         int old_pinned;
 712         u_char old_prio;
 713         int locks __unused;
 714
 715         MPASS(cold || epoch != NULL);
 716         INIT_CHECK(epoch);
 717         td = curthread;
 718 #ifdef INVARIANTS
 719         locks = curthread->td_locks;
 720         MPASS(epoch->e_flags & EPOCH_PREEMPT);
 721         if ((epoch->e_flags & EPOCH_LOCKED) == 0)
 722                 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
 723                     "epoch_wait() can be long running");
 724         KASSERT(!in_epoch(epoch), ("epoch_wait_preempt() called in the middle "
 725             "of an epoch section of the same epoch"));
 726 #endif
 727         DROP_GIANT();
 728         thread_lock(td);
 729
 730         old_cpu = PCPU_GET(cpuid);
 731         old_pinned = td->td_pinned;
 732         old_prio = td->td_priority;
 733         was_bound = sched_is_bound(td);
 734         sched_unbind(td);
 735         td->td_pinned = 0;
 736         sched_bind(td, old_cpu);
 737
 738         ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler_preempt,
 739             NULL);
 740
 741         /* restore CPU binding, if any */
 742         if (was_bound != 0) {
 743                 sched_bind(td, old_cpu);
 744         } else {
 745                 /* get thread back to initial CPU, if any */
 746                 if (old_pinned != 0)
 747                         sched_bind(td, old_cpu);
 748                 sched_unbind(td);
 749         }
 750         /* restore pinned after bind */
 751         td->td_pinned = old_pinned;
 752
 753         /* restore thread priority */
 754         sched_prio(td, old_prio);
 755         thread_unlock(td);
 756         PICKUP_GIANT();
 757         KASSERT(td->td_locks == locks,
 758             ("%d residual locks held", td->td_locks - locks));
 759 }
 760
 761 static void
 762 epoch_block_handler(struct ck_epoch *g __unused, ck_epoch_record_t *c __unused,
 763     void *arg __unused)
 764 {
 765         cpu_spinwait();
 766 }
 767
 768 void
 769 epoch_wait(epoch_t epoch)
 770 {
 771
 772         MPASS(cold || epoch != NULL);
 773         INIT_CHECK(epoch);
 774         MPASS(epoch->e_flags == 0);
 775         critical_enter();
 776         ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler, NULL);
 777         critical_exit();
 778 }
 779
 780 void
 781 epoch_call(epoch_t epoch, epoch_callback_t callback, epoch_context_t ctx)
 782 {
 783         epoch_record_t er;
 784         ck_epoch_entry_t *cb;
 785
 786         cb = (void *)ctx;
 787
 788         MPASS(callback);
 789         /* too early in boot to have epoch set up */
 790         if (__predict_false(epoch == NULL))
 791                 goto boottime;
 792 #if !defined(EARLY_AP_STARTUP)
 793         if (__predict_false(inited < 2))
 794                 goto boottime;
 795 #endif
 796
 797         critical_enter();
 798         *DPCPU_PTR(epoch_cb_count) += 1;
 799         er = epoch_currecord(epoch);
 800         ck_epoch_call(&er->er_record, cb, (ck_epoch_cb_t *)callback);
 801         critical_exit();
 802         return;
 803 boottime:
 804         callback(ctx);
 805 }
 806
 807 static void
 808 epoch_call_task(void *arg __unused)
 809 {
 810         ck_stack_entry_t *cursor, *head, *next;
 811         ck_epoch_record_t *record;
 812         epoch_record_t er;
 813         epoch_t epoch;
 814         ck_stack_t cb_stack;
 815         int i, npending, total;
 816
 817         ck_stack_init(&cb_stack);
 818         critical_enter();
 819         epoch_enter(global_epoch);
 820         for (total = i = 0; i != MAX_EPOCHS; i++) {
 821                 epoch = epoch_array + i;
 822                 if (__predict_false(
 823                     atomic_load_acq_int(&epoch->e_in_use) == 0))
 824                         continue;
 825                 er = epoch_currecord(epoch);
 826                 record = &er->er_record;
 827                 if ((npending = record->n_pending) == 0)
 828                         continue;
 829                 ck_epoch_poll_deferred(record, &cb_stack);
 830                 total += npending - record->n_pending;
 831         }
 832         epoch_exit(global_epoch);
 833         *DPCPU_PTR(epoch_cb_count) -= total;
 834         critical_exit();
 835
 836         counter_u64_add(epoch_call_count, total);
 837         counter_u64_add(epoch_call_task_count, 1);
 838
 839         head = ck_stack_batch_pop_npsc(&cb_stack);
 840         for (cursor = head; cursor != NULL; cursor = next) {
 841                 struct ck_epoch_entry *entry =
 842                     ck_epoch_entry_container(cursor);
 843
 844                 next = CK_STACK_NEXT(cursor);
 845                 entry->function(entry);
 846         }
 847 }
 848
 849 static int
 850 in_epoch_verbose_preempt(epoch_t epoch, int dump_onfail)
 851 {
 852         epoch_record_t er;
 853         struct epoch_tracker *tdwait;
 854         struct thread *td;
 855
 856         MPASS(epoch != NULL);
 857         MPASS((epoch->e_flags & EPOCH_PREEMPT) != 0);
 858         td = curthread;
 859         if (THREAD_CAN_SLEEP())
 860                 return (0);
 861         critical_enter();
 862         er = epoch_currecord(epoch);
 863         TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link)
 864                 if (tdwait->et_td == td) {
 865                         critical_exit();
 866                         return (1);
 867                 }
 868 #ifdef INVARIANTS
 869         if (dump_onfail) {
 870                 MPASS(td->td_pinned);
 871                 printf("cpu: %d id: %d\n", curcpu, td->td_tid);
 872                 TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link)
 873                         printf("td_tid: %d ", tdwait->et_td->td_tid);
 874                 printf("\n");
 875         }
 876 #endif
 877         critical_exit();
 878         return (0);
 879 }
 880
 881 #ifdef INVARIANTS
 882 static void
 883 epoch_assert_nocpu(epoch_t epoch, struct thread *td)
 884 {
 885         epoch_record_t er;
 886         int cpu;
 887         bool crit;
 888
 889         crit = td->td_critnest > 0;
 890
 891         /* Check for a critical section mishap. */
 892         CPU_FOREACH(cpu) {
 893                 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu);
 894                 KASSERT(er->er_td != td,
 895                     ("%s critical section in epoch '%s', from cpu %d",
 896                     (crit ? "exited" : "re-entered"), epoch->e_name, cpu));
 897         }
 898 }
 899 #else
 900 #define epoch_assert_nocpu(e, td) do {} while (0)
 901 #endif
 902
 903 int
 904 in_epoch_verbose(epoch_t epoch, int dump_onfail)
 905 {
 906         epoch_record_t er;
 907         struct thread *td;
 908
 909         if (__predict_false((epoch) == NULL))
 910                 return (0);
 911         if ((epoch->e_flags & EPOCH_PREEMPT) != 0)
 912                 return (in_epoch_verbose_preempt(epoch, dump_onfail));
 913
 914         /*
 915          * The thread being in a critical section is a necessary
 916          * condition to be correctly inside a non-preemptible epoch,
 917          * so it's definitely not in this epoch.
 918          */
 919         td = curthread;
 920         if (td->td_critnest == 0) {
 921                 epoch_assert_nocpu(epoch, td);
 922                 return (0);
 923         }
 924
 925         /*
 926          * The current cpu is in a critical section, so the epoch record will be
 927          * stable for the rest of this function.  Knowing that the record is not
 928          * active is sufficient for knowing whether we're in this epoch or not,
 929          * since it's a pcpu record.
 930          */
 931         er = epoch_currecord(epoch);
 932         if (er->er_record.active == 0) {
 933                 epoch_assert_nocpu(epoch, td);
 934                 return (0);
 935         }
 936
 937         MPASS(er->er_td == td);
 938         return (1);
 939 }
 940
 941 int
 942 in_epoch(epoch_t epoch)
 943 {
 944         return (in_epoch_verbose(epoch, 0));
 945 }
 946
 947 static void
 948 epoch_drain_cb(struct epoch_context *ctx)
 949 {
 950         struct epoch *epoch =
 951             __containerof(ctx, struct epoch_record, er_drain_ctx)->er_parent;
 952
 953         if (atomic_fetchadd_int(&epoch->e_drain_count, -1) == 1) {
 954                 mtx_lock(&epoch->e_drain_mtx);
 955                 wakeup(epoch);
 956                 mtx_unlock(&epoch->e_drain_mtx);
 957         }
 958 }
 959
 960 void
 961 epoch_drain_callbacks(epoch_t epoch)
 962 {
 963         epoch_record_t er;
 964         struct thread *td;
 965         int was_bound;
 966         int old_pinned;
 967         int old_cpu;
 968         int cpu;
 969
 970         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
 971             "epoch_drain_callbacks() may sleep!");
 972
 973         /* too early in boot to have epoch set up */
 974         if (__predict_false(epoch == NULL))
 975                 return;
 976 #if !defined(EARLY_AP_STARTUP)
 977         if (__predict_false(inited < 2))
 978                 return;
 979 #endif
 980         DROP_GIANT();
 981
 982         sx_xlock(&epoch->e_drain_sx);
 983         mtx_lock(&epoch->e_drain_mtx);
 984
 985         td = curthread;
 986         thread_lock(td);
 987         old_cpu = PCPU_GET(cpuid);
 988         old_pinned = td->td_pinned;
 989         was_bound = sched_is_bound(td);
 990         sched_unbind(td);
 991         td->td_pinned = 0;
 992
 993         CPU_FOREACH(cpu)
 994                 epoch->e_drain_count++;
 995         CPU_FOREACH(cpu) {
 996                 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu);
 997                 sched_bind(td, cpu);
 998                 epoch_call(epoch, &epoch_drain_cb, &er->er_drain_ctx);
 999         }
1000
1001         /* restore CPU binding, if any */
1002         if (was_bound != 0) {
1003                 sched_bind(td, old_cpu);
1004         } else {
1005                 /* get thread back to initial CPU, if any */
1006                 if (old_pinned != 0)
1007                         sched_bind(td, old_cpu);
1008                 sched_unbind(td);
1009         }
1010         /* restore pinned after bind */
1011         td->td_pinned = old_pinned;
1012
1013         thread_unlock(td);
1014
1015         while (epoch->e_drain_count != 0)
1016                 msleep(epoch, &epoch->e_drain_mtx, PZERO, "EDRAIN", 0);
1017
1018         mtx_unlock(&epoch->e_drain_mtx);
1019         sx_xunlock(&epoch->e_drain_sx);
1020
1021         PICKUP_GIANT();
1022 }