util/async.c

   1 /*
   2  * Data plane event loop
   3  *
   4  * Copyright (c) 2003-2008 Fabrice Bellard
   5  * Copyright (c) 2009-2017 QEMU contributors
   6  *
   7  * Permission is hereby granted, free of charge, to any person obtaining a copy
   8  * of this software and associated documentation files (the "Software"), to deal
   9  * in the Software without restriction, including without limitation the rights
  10  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  11  * copies of the Software, and to permit persons to whom the Software is
  12  * furnished to do so, subject to the following conditions:
  13  *
  14  * The above copyright notice and this permission notice shall be included in
  15  * all copies or substantial portions of the Software.
  16  *
  17  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  18  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  19  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  20  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  21  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  22  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  23  * THE SOFTWARE.
  24  */
  25
  26 #include "qemu/osdep.h"
  27 #include "qapi/error.h"
  28 #include "block/aio.h"
  29 #include "block/thread-pool.h"
  30 #include "qemu/main-loop.h"
  31 #include "qemu/atomic.h"
  32 #include "qemu/rcu_queue.h"
  33 #include "block/raw-aio.h"
  34 #include "qemu/coroutine_int.h"
  35 #include "trace.h"
  36
  37 /***********************************************************/
  38 /* bottom halves (can be seen as timers which expire ASAP) */
  39
  40 /* QEMUBH::flags values */
  41 enum {
  42     /* Already enqueued and waiting for aio_bh_poll() */
  43     BH_PENDING   = (1 << 0),
  44
  45     /* Invoke the callback */
  46     BH_SCHEDULED = (1 << 1),
  47
  48     /* Delete without invoking callback */
  49     BH_DELETED   = (1 << 2),
  50
  51     /* Delete after invoking callback */
  52     BH_ONESHOT   = (1 << 3),
  53
  54     /* Schedule periodically when the event loop is idle */
  55     BH_IDLE      = (1 << 4),
  56 };
  57
  58 struct QEMUBH {
  59     AioContext *ctx;
  60     QEMUBHFunc *cb;
  61     void *opaque;
  62     QSLIST_ENTRY(QEMUBH) next;
  63     unsigned flags;
  64 };
  65
  66 /* Called concurrently from any thread */
  67 static void aio_bh_enqueue(QEMUBH *bh, unsigned new_flags)
  68 {
  69     AioContext *ctx = bh->ctx;
  70     unsigned old_flags;
  71
  72     /*
  73      * The memory barrier implicit in qatomic_fetch_or makes sure that:
  74      * 1. idle & any writes needed by the callback are done before the
  75      *    locations are read in the aio_bh_poll.
  76      * 2. ctx is loaded before the callback has a chance to execute and bh
  77      *    could be freed.
  78      */
  79     old_flags = qatomic_fetch_or(&bh->flags, BH_PENDING | new_flags);
  80     if (!(old_flags & BH_PENDING)) {
  81         QSLIST_INSERT_HEAD_ATOMIC(&ctx->bh_list, bh, next);
  82     }
  83
  84     aio_notify(ctx);
  85 }
  86
  87 /* Only called from aio_bh_poll() and aio_ctx_finalize() */
  88 static QEMUBH *aio_bh_dequeue(BHList *head, unsigned *flags)
  89 {
  90     QEMUBH *bh = QSLIST_FIRST_RCU(head);
  91
  92     if (!bh) {
  93         return NULL;
  94     }
  95
  96     QSLIST_REMOVE_HEAD(head, next);
  97
  98     /*
  99      * The qatomic_and is paired with aio_bh_enqueue().  The implicit memory
 100      * barrier ensures that the callback sees all writes done by the scheduling
 101      * thread.  It also ensures that the scheduling thread sees the cleared
 102      * flag before bh->cb has run, and thus will call aio_notify again if
 103      * necessary.
 104      */
 105     *flags = qatomic_fetch_and(&bh->flags,
 106                               ~(BH_PENDING | BH_SCHEDULED | BH_IDLE));
 107     return bh;
 108 }
 109
 110 void aio_bh_schedule_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
 111 {
 112     QEMUBH *bh;
 113     bh = g_new(QEMUBH, 1);
 114     *bh = (QEMUBH){
 115         .ctx = ctx,
 116         .cb = cb,
 117         .opaque = opaque,
 118     };
 119     aio_bh_enqueue(bh, BH_SCHEDULED | BH_ONESHOT);
 120 }
 121
 122 QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
 123 {
 124     QEMUBH *bh;
 125     bh = g_new(QEMUBH, 1);
 126     *bh = (QEMUBH){
 127         .ctx = ctx,
 128         .cb = cb,
 129         .opaque = opaque,
 130     };
 131     return bh;
 132 }
 133
 134 void aio_bh_call(QEMUBH *bh)
 135 {
 136     bh->cb(bh->opaque);
 137 }
 138
 139 /* Multiple occurrences of aio_bh_poll cannot be called concurrently. */
 140 int aio_bh_poll(AioContext *ctx)
 141 {
 142     BHListSlice slice;
 143     BHListSlice *s;
 144     int ret = 0;
 145
 146     QSLIST_MOVE_ATOMIC(&slice.bh_list, &ctx->bh_list);
 147     QSIMPLEQ_INSERT_TAIL(&ctx->bh_slice_list, &slice, next);
 148
 149     while ((s = QSIMPLEQ_FIRST(&ctx->bh_slice_list))) {
 150         QEMUBH *bh;
 151         unsigned flags;
 152
 153         bh = aio_bh_dequeue(&s->bh_list, &flags);
 154         if (!bh) {
 155             QSIMPLEQ_REMOVE_HEAD(&ctx->bh_slice_list, next);
 156             continue;
 157         }
 158
 159         if ((flags & (BH_SCHEDULED | BH_DELETED)) == BH_SCHEDULED) {
 160             /* Idle BHs don't count as progress */
 161             if (!(flags & BH_IDLE)) {
 162                 ret = 1;
 163             }
 164             aio_bh_call(bh);
 165         }
 166         if (flags & (BH_DELETED | BH_ONESHOT)) {
 167             g_free(bh);
 168         }
 169     }
 170
 171     return ret;
 172 }
 173
 174 void qemu_bh_schedule_idle(QEMUBH *bh)
 175 {
 176     aio_bh_enqueue(bh, BH_SCHEDULED | BH_IDLE);
 177 }
 178
 179 void qemu_bh_schedule(QEMUBH *bh)
 180 {
 181     aio_bh_enqueue(bh, BH_SCHEDULED);
 182 }
 183
 184 /* This func is async.
 185  */
 186 void qemu_bh_cancel(QEMUBH *bh)
 187 {
 188     qatomic_and(&bh->flags, ~BH_SCHEDULED);
 189 }
 190
 191 /* This func is async.The bottom half will do the delete action at the finial
 192  * end.
 193  */
 194 void qemu_bh_delete(QEMUBH *bh)
 195 {
 196     aio_bh_enqueue(bh, BH_DELETED);
 197 }
 198
 199 static int64_t aio_compute_bh_timeout(BHList *head, int timeout)
 200 {
 201     QEMUBH *bh;
 202
 203     QSLIST_FOREACH_RCU(bh, head, next) {
 204         if ((bh->flags & (BH_SCHEDULED | BH_DELETED)) == BH_SCHEDULED) {
 205             if (bh->flags & BH_IDLE) {
 206                 /* idle bottom halves will be polled at least
 207                  * every 10ms */
 208                 timeout = 10000000;
 209             } else {
 210                 /* non-idle bottom halves will be executed
 211                  * immediately */
 212                 return 0;
 213             }
 214         }
 215     }
 216
 217     return timeout;
 218 }
 219
 220 int64_t
 221 aio_compute_timeout(AioContext *ctx)
 222 {
 223     BHListSlice *s;
 224     int64_t deadline;
 225     int timeout = -1;
 226
 227     timeout = aio_compute_bh_timeout(&ctx->bh_list, timeout);
 228     if (timeout == 0) {
 229         return 0;
 230     }
 231
 232     QSIMPLEQ_FOREACH(s, &ctx->bh_slice_list, next) {
 233         timeout = aio_compute_bh_timeout(&s->bh_list, timeout);
 234         if (timeout == 0) {
 235             return 0;
 236         }
 237     }
 238
 239     deadline = timerlistgroup_deadline_ns(&ctx->tlg);
 240     if (deadline == 0) {
 241         return 0;
 242     } else {
 243         return qemu_soonest_timeout(timeout, deadline);
 244     }
 245 }
 246
 247 static gboolean
 248 aio_ctx_prepare(GSource *source, gint    *timeout)
 249 {
 250     AioContext *ctx = (AioContext *) source;
 251
 252     qatomic_set(&ctx->notify_me, qatomic_read(&ctx->notify_me) | 1);
 253
 254     /*
 255      * Write ctx->notify_me before computing the timeout
 256      * (reading bottom half flags, etc.).  Pairs with
 257      * smp_mb in aio_notify().
 258      */
 259     smp_mb();
 260
 261     /* We assume there is no timeout already supplied */
 262     *timeout = qemu_timeout_ns_to_ms(aio_compute_timeout(ctx));
 263
 264     if (aio_prepare(ctx)) {
 265         *timeout = 0;
 266     }
 267
 268     return *timeout == 0;
 269 }
 270
 271 static gboolean
 272 aio_ctx_check(GSource *source)
 273 {
 274     AioContext *ctx = (AioContext *) source;
 275     QEMUBH *bh;
 276     BHListSlice *s;
 277
 278     /* Finish computing the timeout before clearing the flag.  */
 279     qatomic_store_release(&ctx->notify_me, qatomic_read(&ctx->notify_me) & ~1);
 280     aio_notify_accept(ctx);
 281
 282     QSLIST_FOREACH_RCU(bh, &ctx->bh_list, next) {
 283         if ((bh->flags & (BH_SCHEDULED | BH_DELETED)) == BH_SCHEDULED) {
 284             return true;
 285         }
 286     }
 287
 288     QSIMPLEQ_FOREACH(s, &ctx->bh_slice_list, next) {
 289         QSLIST_FOREACH_RCU(bh, &s->bh_list, next) {
 290             if ((bh->flags & (BH_SCHEDULED | BH_DELETED)) == BH_SCHEDULED) {
 291                 return true;
 292             }
 293         }
 294     }
 295     return aio_pending(ctx) || (timerlistgroup_deadline_ns(&ctx->tlg) == 0);
 296 }
 297
 298 static gboolean
 299 aio_ctx_dispatch(GSource     *source,
 300                  GSourceFunc  callback,
 301                  gpointer     user_data)
 302 {
 303     AioContext *ctx = (AioContext *) source;
 304
 305     assert(callback == NULL);
 306     aio_dispatch(ctx);
 307     return true;
 308 }
 309
 310 static void
 311 aio_ctx_finalize(GSource     *source)
 312 {
 313     AioContext *ctx = (AioContext *) source;
 314     QEMUBH *bh;
 315     unsigned flags;
 316
 317     thread_pool_free(ctx->thread_pool);
 318
 319 #ifdef CONFIG_LINUX_AIO
 320     if (ctx->linux_aio) {
 321         laio_detach_aio_context(ctx->linux_aio, ctx);
 322         laio_cleanup(ctx->linux_aio);
 323         ctx->linux_aio = NULL;
 324     }
 325 #endif
 326
 327 #ifdef CONFIG_LINUX_IO_URING
 328     if (ctx->linux_io_uring) {
 329         luring_detach_aio_context(ctx->linux_io_uring, ctx);
 330         luring_cleanup(ctx->linux_io_uring);
 331         ctx->linux_io_uring = NULL;
 332     }
 333 #endif
 334
 335     assert(QSLIST_EMPTY(&ctx->scheduled_coroutines));
 336     qemu_bh_delete(ctx->co_schedule_bh);
 337
 338     /* There must be no aio_bh_poll() calls going on */
 339     assert(QSIMPLEQ_EMPTY(&ctx->bh_slice_list));
 340
 341     while ((bh = aio_bh_dequeue(&ctx->bh_list, &flags))) {
 342         /* qemu_bh_delete() must have been called on BHs in this AioContext */
 343         assert(flags & BH_DELETED);
 344
 345         g_free(bh);
 346     }
 347
 348     aio_set_event_notifier(ctx, &ctx->notifier, false, NULL, NULL);
 349     event_notifier_cleanup(&ctx->notifier);
 350     qemu_rec_mutex_destroy(&ctx->lock);
 351     qemu_lockcnt_destroy(&ctx->list_lock);
 352     timerlistgroup_deinit(&ctx->tlg);
 353     aio_context_destroy(ctx);
 354 }
 355
 356 static GSourceFuncs aio_source_funcs = {
 357     aio_ctx_prepare,
 358     aio_ctx_check,
 359     aio_ctx_dispatch,
 360     aio_ctx_finalize
 361 };
 362
 363 GSource *aio_get_g_source(AioContext *ctx)
 364 {
 365     aio_context_use_g_source(ctx);
 366     g_source_ref(&ctx->source);
 367     return &ctx->source;
 368 }
 369
 370 ThreadPool *aio_get_thread_pool(AioContext *ctx)
 371 {
 372     if (!ctx->thread_pool) {
 373         ctx->thread_pool = thread_pool_new(ctx);
 374     }
 375     return ctx->thread_pool;
 376 }
 377
 378 #ifdef CONFIG_LINUX_AIO
 379 LinuxAioState *aio_setup_linux_aio(AioContext *ctx, Error **errp)
 380 {
 381     if (!ctx->linux_aio) {
 382         ctx->linux_aio = laio_init(errp);
 383         if (ctx->linux_aio) {
 384             laio_attach_aio_context(ctx->linux_aio, ctx);
 385         }
 386     }
 387     return ctx->linux_aio;
 388 }
 389
 390 LinuxAioState *aio_get_linux_aio(AioContext *ctx)
 391 {
 392     assert(ctx->linux_aio);
 393     return ctx->linux_aio;
 394 }
 395 #endif
 396
 397 #ifdef CONFIG_LINUX_IO_URING
 398 LuringState *aio_setup_linux_io_uring(AioContext *ctx, Error **errp)
 399 {
 400     if (ctx->linux_io_uring) {
 401         return ctx->linux_io_uring;
 402     }
 403
 404     ctx->linux_io_uring = luring_init(errp);
 405     if (!ctx->linux_io_uring) {
 406         return NULL;
 407     }
 408
 409     luring_attach_aio_context(ctx->linux_io_uring, ctx);
 410     return ctx->linux_io_uring;
 411 }
 412
 413 LuringState *aio_get_linux_io_uring(AioContext *ctx)
 414 {
 415     assert(ctx->linux_io_uring);
 416     return ctx->linux_io_uring;
 417 }
 418 #endif
 419
 420 void aio_notify(AioContext *ctx)
 421 {
 422     /*
 423      * Write e.g. bh->flags before writing ctx->notified.  Pairs with smp_mb in
 424      * aio_notify_accept.
 425      */
 426     smp_wmb();
 427     qatomic_set(&ctx->notified, true);
 428
 429     /*
 430      * Write ctx->notified before reading ctx->notify_me.  Pairs
 431      * with smp_mb in aio_ctx_prepare or aio_poll.
 432      */
 433     smp_mb();
 434     if (qatomic_read(&ctx->notify_me)) {
 435         event_notifier_set(&ctx->notifier);
 436     }
 437 }
 438
 439 void aio_notify_accept(AioContext *ctx)
 440 {
 441     qatomic_set(&ctx->notified, false);
 442
 443     /*
 444      * Write ctx->notified before reading e.g. bh->flags.  Pairs with smp_wmb
 445      * in aio_notify.
 446      */
 447     smp_mb();
 448 }
 449
 450 static void aio_timerlist_notify(void *opaque, QEMUClockType type)
 451 {
 452     aio_notify(opaque);
 453 }
 454
 455 static void aio_context_notifier_cb(EventNotifier *e)
 456 {
 457     AioContext *ctx = container_of(e, AioContext, notifier);
 458
 459     event_notifier_test_and_clear(&ctx->notifier);
 460 }
 461
 462 /* Returns true if aio_notify() was called (e.g. a BH was scheduled) */
 463 static bool aio_context_notifier_poll(void *opaque)
 464 {
 465     EventNotifier *e = opaque;
 466     AioContext *ctx = container_of(e, AioContext, notifier);
 467
 468     return qatomic_read(&ctx->notified);
 469 }
 470
 471 static void co_schedule_bh_cb(void *opaque)
 472 {
 473     AioContext *ctx = opaque;
 474     QSLIST_HEAD(, Coroutine) straight, reversed;
 475
 476     QSLIST_MOVE_ATOMIC(&reversed, &ctx->scheduled_coroutines);
 477     QSLIST_INIT(&straight);
 478
 479     while (!QSLIST_EMPTY(&reversed)) {
 480         Coroutine *co = QSLIST_FIRST(&reversed);
 481         QSLIST_REMOVE_HEAD(&reversed, co_scheduled_next);
 482         QSLIST_INSERT_HEAD(&straight, co, co_scheduled_next);
 483     }
 484
 485     while (!QSLIST_EMPTY(&straight)) {
 486         Coroutine *co = QSLIST_FIRST(&straight);
 487         QSLIST_REMOVE_HEAD(&straight, co_scheduled_next);
 488         trace_aio_co_schedule_bh_cb(ctx, co);
 489         aio_context_acquire(ctx);
 490
 491         /* Protected by write barrier in qemu_aio_coroutine_enter */
 492         qatomic_set(&co->scheduled, NULL);
 493         qemu_aio_coroutine_enter(ctx, co);
 494         aio_context_release(ctx);
 495     }
 496 }
 497
 498 AioContext *aio_context_new(Error **errp)
 499 {
 500     int ret;
 501     AioContext *ctx;
 502
 503     ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
 504     QSLIST_INIT(&ctx->bh_list);
 505     QSIMPLEQ_INIT(&ctx->bh_slice_list);
 506     aio_context_setup(ctx);
 507
 508     ret = event_notifier_init(&ctx->notifier, false);
 509     if (ret < 0) {
 510         error_setg_errno(errp, -ret, "Failed to initialize event notifier");
 511         goto fail;
 512     }
 513     g_source_set_can_recurse(&ctx->source, true);
 514     qemu_lockcnt_init(&ctx->list_lock);
 515
 516     ctx->co_schedule_bh = aio_bh_new(ctx, co_schedule_bh_cb, ctx);
 517     QSLIST_INIT(&ctx->scheduled_coroutines);
 518
 519     aio_set_event_notifier(ctx, &ctx->notifier,
 520                            false,
 521                            aio_context_notifier_cb,
 522                            aio_context_notifier_poll);
 523 #ifdef CONFIG_LINUX_AIO
 524     ctx->linux_aio = NULL;
 525 #endif
 526
 527 #ifdef CONFIG_LINUX_IO_URING
 528     ctx->linux_io_uring = NULL;
 529 #endif
 530
 531     ctx->thread_pool = NULL;
 532     qemu_rec_mutex_init(&ctx->lock);
 533     timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx);
 534
 535     ctx->poll_ns = 0;
 536     ctx->poll_max_ns = 0;
 537     ctx->poll_grow = 0;
 538     ctx->poll_shrink = 0;
 539
 540     return ctx;
 541 fail:
 542     g_source_destroy(&ctx->source);
 543     return NULL;
 544 }
 545
 546 void aio_co_schedule(AioContext *ctx, Coroutine *co)
 547 {
 548     trace_aio_co_schedule(ctx, co);
 549     const char *scheduled = qatomic_cmpxchg(&co->scheduled, NULL,
 550                                            __func__);
 551
 552     if (scheduled) {
 553         fprintf(stderr,
 554                 "%s: Co-routine was already scheduled in '%s'\n",
 555                 __func__, scheduled);
 556         abort();
 557     }
 558
 559     /* The coroutine might run and release the last ctx reference before we
 560      * invoke qemu_bh_schedule().  Take a reference to keep ctx alive until
 561      * we're done.
 562      */
 563     aio_context_ref(ctx);
 564
 565     QSLIST_INSERT_HEAD_ATOMIC(&ctx->scheduled_coroutines,
 566                               co, co_scheduled_next);
 567     qemu_bh_schedule(ctx->co_schedule_bh);
 568
 569     aio_context_unref(ctx);
 570 }
 571
 572 typedef struct AioCoRescheduleSelf {
 573     Coroutine *co;
 574     AioContext *new_ctx;
 575 } AioCoRescheduleSelf;
 576
 577 static void aio_co_reschedule_self_bh(void *opaque)
 578 {
 579     AioCoRescheduleSelf *data = opaque;
 580     aio_co_schedule(data->new_ctx, data->co);
 581 }
 582
 583 void coroutine_fn aio_co_reschedule_self(AioContext *new_ctx)
 584 {
 585     AioContext *old_ctx = qemu_get_current_aio_context();
 586
 587     if (old_ctx != new_ctx) {
 588         AioCoRescheduleSelf data = {
 589             .co = qemu_coroutine_self(),
 590             .new_ctx = new_ctx,
 591         };
 592         /*
 593          * We can't directly schedule the coroutine in the target context
 594          * because this would be racy: The other thread could try to enter the
 595          * coroutine before it has yielded in this one.
 596          */
 597         aio_bh_schedule_oneshot(old_ctx, aio_co_reschedule_self_bh, &data);
 598         qemu_coroutine_yield();
 599     }
 600 }
 601
 602 void aio_co_wake(struct Coroutine *co)
 603 {
 604     AioContext *ctx;
 605
 606     /* Read coroutine before co->ctx.  Matches smp_wmb in
 607      * qemu_coroutine_enter.
 608      */
 609     smp_read_barrier_depends();
 610     ctx = qatomic_read(&co->ctx);
 611
 612     aio_co_enter(ctx, co);
 613 }
 614
 615 void aio_co_enter(AioContext *ctx, struct Coroutine *co)
 616 {
 617     if (ctx != qemu_get_current_aio_context()) {
 618         aio_co_schedule(ctx, co);
 619         return;
 620     }
 621
 622     if (qemu_in_coroutine()) {
 623         Coroutine *self = qemu_coroutine_self();
 624         assert(self != co);
 625         QSIMPLEQ_INSERT_TAIL(&self->co_queue_wakeup, co, co_queue_next);
 626     } else {
 627         aio_context_acquire(ctx);
 628         qemu_aio_coroutine_enter(ctx, co);
 629         aio_context_release(ctx);
 630     }
 631 }
 632
 633 void aio_context_ref(AioContext *ctx)
 634 {
 635     g_source_ref(&ctx->source);
 636 }
 637
 638 void aio_context_unref(AioContext *ctx)
 639 {
 640     g_source_unref(&ctx->source);
 641 }
 642
 643 void aio_context_acquire(AioContext *ctx)
 644 {
 645     qemu_rec_mutex_lock(&ctx->lock);
 646 }
 647
 648 void aio_context_release(AioContext *ctx)
 649 {
 650     qemu_rec_mutex_unlock(&ctx->lock);
 651 }
 652
 653 static __thread AioContext *my_aiocontext;
 654
 655 AioContext *qemu_get_current_aio_context(void)
 656 {
 657     if (my_aiocontext) {
 658         return my_aiocontext;
 659     }
 660     if (qemu_mutex_iothread_locked()) {
 661         /* Possibly in a vCPU thread.  */
 662         return qemu_get_aio_context();
 663     }
 664     return NULL;
 665 }
 666
 667 void qemu_set_current_aio_context(AioContext *ctx)
 668 {
 669     assert(!my_aiocontext);
 670     my_aiocontext = ctx;
 671 }