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 "qemu/coroutine-tls.h"
  36 #include "trace.h"
  37
  38 /***********************************************************/
  39 /* bottom halves (can be seen as timers which expire ASAP) */
  40
  41 /* QEMUBH::flags values */
  42 enum {
  43     /* Already enqueued and waiting for aio_bh_poll() */
  44     BH_PENDING   = (1 << 0),
  45
  46     /* Invoke the callback */
  47     BH_SCHEDULED = (1 << 1),
  48
  49     /* Delete without invoking callback */
  50     BH_DELETED   = (1 << 2),
  51
  52     /* Delete after invoking callback */
  53     BH_ONESHOT   = (1 << 3),
  54
  55     /* Schedule periodically when the event loop is idle */
  56     BH_IDLE      = (1 << 4),
  57 };
  58
  59 struct QEMUBH {
  60     AioContext *ctx;
  61     const char *name;
  62     QEMUBHFunc *cb;
  63     void *opaque;
  64     QSLIST_ENTRY(QEMUBH) next;
  65     unsigned flags;
  66 };
  67
  68 /* Called concurrently from any thread */
  69 static void aio_bh_enqueue(QEMUBH *bh, unsigned new_flags)
  70 {
  71     AioContext *ctx = bh->ctx;
  72     unsigned old_flags;
  73
  74     /*
  75      * The memory barrier implicit in qatomic_fetch_or makes sure that:
  76      * 1. idle & any writes needed by the callback are done before the
  77      *    locations are read in the aio_bh_poll.
  78      * 2. ctx is loaded before the callback has a chance to execute and bh
  79      *    could be freed.
  80      */
  81     old_flags = qatomic_fetch_or(&bh->flags, BH_PENDING | new_flags);
  82     if (!(old_flags & BH_PENDING)) {
  83         QSLIST_INSERT_HEAD_ATOMIC(&ctx->bh_list, bh, next);
  84     }
  85
  86     aio_notify(ctx);
  87 }
  88
  89 /* Only called from aio_bh_poll() and aio_ctx_finalize() */
  90 static QEMUBH *aio_bh_dequeue(BHList *head, unsigned *flags)
  91 {
  92     QEMUBH *bh = QSLIST_FIRST_RCU(head);
  93
  94     if (!bh) {
  95         return NULL;
  96     }
  97
  98     QSLIST_REMOVE_HEAD(head, next);
  99
 100     /*
 101      * The qatomic_and is paired with aio_bh_enqueue().  The implicit memory
 102      * barrier ensures that the callback sees all writes done by the scheduling
 103      * thread.  It also ensures that the scheduling thread sees the cleared
 104      * flag before bh->cb has run, and thus will call aio_notify again if
 105      * necessary.
 106      */
 107     *flags = qatomic_fetch_and(&bh->flags,
 108                               ~(BH_PENDING | BH_SCHEDULED | BH_IDLE));
 109     return bh;
 110 }
 111
 112 void aio_bh_schedule_oneshot_full(AioContext *ctx, QEMUBHFunc *cb,
 113                                   void *opaque, const char *name)
 114 {
 115     QEMUBH *bh;
 116     bh = g_new(QEMUBH, 1);
 117     *bh = (QEMUBH){
 118         .ctx = ctx,
 119         .cb = cb,
 120         .opaque = opaque,
 121         .name = name,
 122     };
 123     aio_bh_enqueue(bh, BH_SCHEDULED | BH_ONESHOT);
 124 }
 125
 126 QEMUBH *aio_bh_new_full(AioContext *ctx, QEMUBHFunc *cb, void *opaque,
 127                         const char *name)
 128 {
 129     QEMUBH *bh;
 130     bh = g_new(QEMUBH, 1);
 131     *bh = (QEMUBH){
 132         .ctx = ctx,
 133         .cb = cb,
 134         .opaque = opaque,
 135         .name = name,
 136     };
 137     return bh;
 138 }
 139
 140 void aio_bh_call(QEMUBH *bh)
 141 {
 142     bh->cb(bh->opaque);
 143 }
 144
 145 /* Multiple occurrences of aio_bh_poll cannot be called concurrently. */
 146 int aio_bh_poll(AioContext *ctx)
 147 {
 148     BHListSlice slice;
 149     BHListSlice *s;
 150     int ret = 0;
 151
 152     QSLIST_MOVE_ATOMIC(&slice.bh_list, &ctx->bh_list);
 153     QSIMPLEQ_INSERT_TAIL(&ctx->bh_slice_list, &slice, next);
 154
 155     while ((s = QSIMPLEQ_FIRST(&ctx->bh_slice_list))) {
 156         QEMUBH *bh;
 157         unsigned flags;
 158
 159         bh = aio_bh_dequeue(&s->bh_list, &flags);
 160         if (!bh) {
 161             QSIMPLEQ_REMOVE_HEAD(&ctx->bh_slice_list, next);
 162             continue;
 163         }
 164
 165         if ((flags & (BH_SCHEDULED | BH_DELETED)) == BH_SCHEDULED) {
 166             /* Idle BHs don't count as progress */
 167             if (!(flags & BH_IDLE)) {
 168                 ret = 1;
 169             }
 170             aio_bh_call(bh);
 171         }
 172         if (flags & (BH_DELETED | BH_ONESHOT)) {
 173             g_free(bh);
 174         }
 175     }
 176
 177     return ret;
 178 }
 179
 180 void qemu_bh_schedule_idle(QEMUBH *bh)
 181 {
 182     aio_bh_enqueue(bh, BH_SCHEDULED | BH_IDLE);
 183 }
 184
 185 void qemu_bh_schedule(QEMUBH *bh)
 186 {
 187     aio_bh_enqueue(bh, BH_SCHEDULED);
 188 }
 189
 190 /* This func is async.
 191  */
 192 void qemu_bh_cancel(QEMUBH *bh)
 193 {
 194     qatomic_and(&bh->flags, ~BH_SCHEDULED);
 195 }
 196
 197 /* This func is async.The bottom half will do the delete action at the finial
 198  * end.
 199  */
 200 void qemu_bh_delete(QEMUBH *bh)
 201 {
 202     aio_bh_enqueue(bh, BH_DELETED);
 203 }
 204
 205 static int64_t aio_compute_bh_timeout(BHList *head, int timeout)
 206 {
 207     QEMUBH *bh;
 208
 209     QSLIST_FOREACH_RCU(bh, head, next) {
 210         if ((bh->flags & (BH_SCHEDULED | BH_DELETED)) == BH_SCHEDULED) {
 211             if (bh->flags & BH_IDLE) {
 212                 /* idle bottom halves will be polled at least
 213                  * every 10ms */
 214                 timeout = 10000000;
 215             } else {
 216                 /* non-idle bottom halves will be executed
 217                  * immediately */
 218                 return 0;
 219             }
 220         }
 221     }
 222
 223     return timeout;
 224 }
 225
 226 int64_t
 227 aio_compute_timeout(AioContext *ctx)
 228 {
 229     BHListSlice *s;
 230     int64_t deadline;
 231     int timeout = -1;
 232
 233     timeout = aio_compute_bh_timeout(&ctx->bh_list, timeout);
 234     if (timeout == 0) {
 235         return 0;
 236     }
 237
 238     QSIMPLEQ_FOREACH(s, &ctx->bh_slice_list, next) {
 239         timeout = aio_compute_bh_timeout(&s->bh_list, timeout);
 240         if (timeout == 0) {
 241             return 0;
 242         }
 243     }
 244
 245     deadline = timerlistgroup_deadline_ns(&ctx->tlg);
 246     if (deadline == 0) {
 247         return 0;
 248     } else {
 249         return qemu_soonest_timeout(timeout, deadline);
 250     }
 251 }
 252
 253 static gboolean
 254 aio_ctx_prepare(GSource *source, gint    *timeout)
 255 {
 256     AioContext *ctx = (AioContext *) source;
 257
 258     qatomic_set(&ctx->notify_me, qatomic_read(&ctx->notify_me) | 1);
 259
 260     /*
 261      * Write ctx->notify_me before computing the timeout
 262      * (reading bottom half flags, etc.).  Pairs with
 263      * smp_mb in aio_notify().
 264      */
 265     smp_mb();
 266
 267     /* We assume there is no timeout already supplied */
 268     *timeout = qemu_timeout_ns_to_ms(aio_compute_timeout(ctx));
 269
 270     if (aio_prepare(ctx)) {
 271         *timeout = 0;
 272     }
 273
 274     return *timeout == 0;
 275 }
 276
 277 static gboolean
 278 aio_ctx_check(GSource *source)
 279 {
 280     AioContext *ctx = (AioContext *) source;
 281     QEMUBH *bh;
 282     BHListSlice *s;
 283
 284     /* Finish computing the timeout before clearing the flag.  */
 285     qatomic_store_release(&ctx->notify_me, qatomic_read(&ctx->notify_me) & ~1);
 286     aio_notify_accept(ctx);
 287
 288     QSLIST_FOREACH_RCU(bh, &ctx->bh_list, next) {
 289         if ((bh->flags & (BH_SCHEDULED | BH_DELETED)) == BH_SCHEDULED) {
 290             return true;
 291         }
 292     }
 293
 294     QSIMPLEQ_FOREACH(s, &ctx->bh_slice_list, next) {
 295         QSLIST_FOREACH_RCU(bh, &s->bh_list, next) {
 296             if ((bh->flags & (BH_SCHEDULED | BH_DELETED)) == BH_SCHEDULED) {
 297                 return true;
 298             }
 299         }
 300     }
 301     return aio_pending(ctx) || (timerlistgroup_deadline_ns(&ctx->tlg) == 0);
 302 }
 303
 304 static gboolean
 305 aio_ctx_dispatch(GSource     *source,
 306                  GSourceFunc  callback,
 307                  gpointer     user_data)
 308 {
 309     AioContext *ctx = (AioContext *) source;
 310
 311     assert(callback == NULL);
 312     aio_dispatch(ctx);
 313     return true;
 314 }
 315
 316 static void
 317 aio_ctx_finalize(GSource     *source)
 318 {
 319     AioContext *ctx = (AioContext *) source;
 320     QEMUBH *bh;
 321     unsigned flags;
 322
 323     thread_pool_free(ctx->thread_pool);
 324
 325 #ifdef CONFIG_LINUX_AIO
 326     if (ctx->linux_aio) {
 327         laio_detach_aio_context(ctx->linux_aio, ctx);
 328         laio_cleanup(ctx->linux_aio);
 329         ctx->linux_aio = NULL;
 330     }
 331 #endif
 332
 333 #ifdef CONFIG_LINUX_IO_URING
 334     if (ctx->linux_io_uring) {
 335         luring_detach_aio_context(ctx->linux_io_uring, ctx);
 336         luring_cleanup(ctx->linux_io_uring);
 337         ctx->linux_io_uring = NULL;
 338     }
 339 #endif
 340
 341     assert(QSLIST_EMPTY(&ctx->scheduled_coroutines));
 342     qemu_bh_delete(ctx->co_schedule_bh);
 343
 344     /* There must be no aio_bh_poll() calls going on */
 345     assert(QSIMPLEQ_EMPTY(&ctx->bh_slice_list));
 346
 347     while ((bh = aio_bh_dequeue(&ctx->bh_list, &flags))) {
 348         /*
 349          * qemu_bh_delete() must have been called on BHs in this AioContext. In
 350          * many cases memory leaks, hangs, or inconsistent state occur when a
 351          * BH is leaked because something still expects it to run.
 352          *
 353          * If you hit this, fix the lifecycle of the BH so that
 354          * qemu_bh_delete() and any associated cleanup is called before the
 355          * AioContext is finalized.
 356          */
 357         if (unlikely(!(flags & BH_DELETED))) {
 358             fprintf(stderr, "%s: BH '%s' leaked, aborting...\n",
 359                     __func__, bh->name);
 360             abort();
 361         }
 362
 363         g_free(bh);
 364     }
 365
 366     aio_set_event_notifier(ctx, &ctx->notifier, false, NULL, NULL, NULL);
 367     event_notifier_cleanup(&ctx->notifier);
 368     qemu_rec_mutex_destroy(&ctx->lock);
 369     qemu_lockcnt_destroy(&ctx->list_lock);
 370     timerlistgroup_deinit(&ctx->tlg);
 371     aio_context_destroy(ctx);
 372 }
 373
 374 static GSourceFuncs aio_source_funcs = {
 375     aio_ctx_prepare,
 376     aio_ctx_check,
 377     aio_ctx_dispatch,
 378     aio_ctx_finalize
 379 };
 380
 381 GSource *aio_get_g_source(AioContext *ctx)
 382 {
 383     aio_context_use_g_source(ctx);
 384     g_source_ref(&ctx->source);
 385     return &ctx->source;
 386 }
 387
 388 ThreadPool *aio_get_thread_pool(AioContext *ctx)
 389 {
 390     if (!ctx->thread_pool) {
 391         ctx->thread_pool = thread_pool_new(ctx);
 392     }
 393     return ctx->thread_pool;
 394 }
 395
 396 #ifdef CONFIG_LINUX_AIO
 397 LinuxAioState *aio_setup_linux_aio(AioContext *ctx, Error **errp)
 398 {
 399     if (!ctx->linux_aio) {
 400         ctx->linux_aio = laio_init(errp);
 401         if (ctx->linux_aio) {
 402             laio_attach_aio_context(ctx->linux_aio, ctx);
 403         }
 404     }
 405     return ctx->linux_aio;
 406 }
 407
 408 LinuxAioState *aio_get_linux_aio(AioContext *ctx)
 409 {
 410     assert(ctx->linux_aio);
 411     return ctx->linux_aio;
 412 }
 413 #endif
 414
 415 #ifdef CONFIG_LINUX_IO_URING
 416 LuringState *aio_setup_linux_io_uring(AioContext *ctx, Error **errp)
 417 {
 418     if (ctx->linux_io_uring) {
 419         return ctx->linux_io_uring;
 420     }
 421
 422     ctx->linux_io_uring = luring_init(errp);
 423     if (!ctx->linux_io_uring) {
 424         return NULL;
 425     }
 426
 427     luring_attach_aio_context(ctx->linux_io_uring, ctx);
 428     return ctx->linux_io_uring;
 429 }
 430
 431 LuringState *aio_get_linux_io_uring(AioContext *ctx)
 432 {
 433     assert(ctx->linux_io_uring);
 434     return ctx->linux_io_uring;
 435 }
 436 #endif
 437
 438 void aio_notify(AioContext *ctx)
 439 {
 440     /*
 441      * Write e.g. bh->flags before writing ctx->notified.  Pairs with smp_mb in
 442      * aio_notify_accept.
 443      */
 444     smp_wmb();
 445     qatomic_set(&ctx->notified, true);
 446
 447     /*
 448      * Write ctx->notified before reading ctx->notify_me.  Pairs
 449      * with smp_mb in aio_ctx_prepare or aio_poll.
 450      */
 451     smp_mb();
 452     if (qatomic_read(&ctx->notify_me)) {
 453         event_notifier_set(&ctx->notifier);
 454     }
 455 }
 456
 457 void aio_notify_accept(AioContext *ctx)
 458 {
 459     qatomic_set(&ctx->notified, false);
 460
 461     /*
 462      * Write ctx->notified before reading e.g. bh->flags.  Pairs with smp_wmb
 463      * in aio_notify.
 464      */
 465     smp_mb();
 466 }
 467
 468 static void aio_timerlist_notify(void *opaque, QEMUClockType type)
 469 {
 470     aio_notify(opaque);
 471 }
 472
 473 static void aio_context_notifier_cb(EventNotifier *e)
 474 {
 475     AioContext *ctx = container_of(e, AioContext, notifier);
 476
 477     event_notifier_test_and_clear(&ctx->notifier);
 478 }
 479
 480 /* Returns true if aio_notify() was called (e.g. a BH was scheduled) */
 481 static bool aio_context_notifier_poll(void *opaque)
 482 {
 483     EventNotifier *e = opaque;
 484     AioContext *ctx = container_of(e, AioContext, notifier);
 485
 486     return qatomic_read(&ctx->notified);
 487 }
 488
 489 static void aio_context_notifier_poll_ready(EventNotifier *e)
 490 {
 491     /* Do nothing, we just wanted to kick the event loop */
 492 }
 493
 494 static void co_schedule_bh_cb(void *opaque)
 495 {
 496     AioContext *ctx = opaque;
 497     QSLIST_HEAD(, Coroutine) straight, reversed;
 498
 499     QSLIST_MOVE_ATOMIC(&reversed, &ctx->scheduled_coroutines);
 500     QSLIST_INIT(&straight);
 501
 502     while (!QSLIST_EMPTY(&reversed)) {
 503         Coroutine *co = QSLIST_FIRST(&reversed);
 504         QSLIST_REMOVE_HEAD(&reversed, co_scheduled_next);
 505         QSLIST_INSERT_HEAD(&straight, co, co_scheduled_next);
 506     }
 507
 508     while (!QSLIST_EMPTY(&straight)) {
 509         Coroutine *co = QSLIST_FIRST(&straight);
 510         QSLIST_REMOVE_HEAD(&straight, co_scheduled_next);
 511         trace_aio_co_schedule_bh_cb(ctx, co);
 512         aio_context_acquire(ctx);
 513
 514         /* Protected by write barrier in qemu_aio_coroutine_enter */
 515         qatomic_set(&co->scheduled, NULL);
 516         qemu_aio_coroutine_enter(ctx, co);
 517         aio_context_release(ctx);
 518     }
 519 }
 520
 521 AioContext *aio_context_new(Error **errp)
 522 {
 523     int ret;
 524     AioContext *ctx;
 525
 526     ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
 527     QSLIST_INIT(&ctx->bh_list);
 528     QSIMPLEQ_INIT(&ctx->bh_slice_list);
 529     aio_context_setup(ctx);
 530
 531     ret = event_notifier_init(&ctx->notifier, false);
 532     if (ret < 0) {
 533         error_setg_errno(errp, -ret, "Failed to initialize event notifier");
 534         goto fail;
 535     }
 536     g_source_set_can_recurse(&ctx->source, true);
 537     qemu_lockcnt_init(&ctx->list_lock);
 538
 539     ctx->co_schedule_bh = aio_bh_new(ctx, co_schedule_bh_cb, ctx);
 540     QSLIST_INIT(&ctx->scheduled_coroutines);
 541
 542     aio_set_event_notifier(ctx, &ctx->notifier,
 543                            false,
 544                            aio_context_notifier_cb,
 545                            aio_context_notifier_poll,
 546                            aio_context_notifier_poll_ready);
 547 #ifdef CONFIG_LINUX_AIO
 548     ctx->linux_aio = NULL;
 549 #endif
 550
 551 #ifdef CONFIG_LINUX_IO_URING
 552     ctx->linux_io_uring = NULL;
 553 #endif
 554
 555     ctx->thread_pool = NULL;
 556     qemu_rec_mutex_init(&ctx->lock);
 557     timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx);
 558
 559     ctx->poll_ns = 0;
 560     ctx->poll_max_ns = 0;
 561     ctx->poll_grow = 0;
 562     ctx->poll_shrink = 0;
 563
 564     ctx->aio_max_batch = 0;
 565
 566     return ctx;
 567 fail:
 568     g_source_destroy(&ctx->source);
 569     return NULL;
 570 }
 571
 572 void aio_co_schedule(AioContext *ctx, Coroutine *co)
 573 {
 574     trace_aio_co_schedule(ctx, co);
 575     const char *scheduled = qatomic_cmpxchg(&co->scheduled, NULL,
 576                                            __func__);
 577
 578     if (scheduled) {
 579         fprintf(stderr,
 580                 "%s: Co-routine was already scheduled in '%s'\n",
 581                 __func__, scheduled);
 582         abort();
 583     }
 584
 585     /* The coroutine might run and release the last ctx reference before we
 586      * invoke qemu_bh_schedule().  Take a reference to keep ctx alive until
 587      * we're done.
 588      */
 589     aio_context_ref(ctx);
 590
 591     QSLIST_INSERT_HEAD_ATOMIC(&ctx->scheduled_coroutines,
 592                               co, co_scheduled_next);
 593     qemu_bh_schedule(ctx->co_schedule_bh);
 594
 595     aio_context_unref(ctx);
 596 }
 597
 598 typedef struct AioCoRescheduleSelf {
 599     Coroutine *co;
 600     AioContext *new_ctx;
 601 } AioCoRescheduleSelf;
 602
 603 static void aio_co_reschedule_self_bh(void *opaque)
 604 {
 605     AioCoRescheduleSelf *data = opaque;
 606     aio_co_schedule(data->new_ctx, data->co);
 607 }
 608
 609 void coroutine_fn aio_co_reschedule_self(AioContext *new_ctx)
 610 {
 611     AioContext *old_ctx = qemu_get_current_aio_context();
 612
 613     if (old_ctx != new_ctx) {
 614         AioCoRescheduleSelf data = {
 615             .co = qemu_coroutine_self(),
 616             .new_ctx = new_ctx,
 617         };
 618         /*
 619          * We can't directly schedule the coroutine in the target context
 620          * because this would be racy: The other thread could try to enter the
 621          * coroutine before it has yielded in this one.
 622          */
 623         aio_bh_schedule_oneshot(old_ctx, aio_co_reschedule_self_bh, &data);
 624         qemu_coroutine_yield();
 625     }
 626 }
 627
 628 void aio_co_wake(struct Coroutine *co)
 629 {
 630     AioContext *ctx;
 631
 632     /* Read coroutine before co->ctx.  Matches smp_wmb in
 633      * qemu_coroutine_enter.
 634      */
 635     smp_read_barrier_depends();
 636     ctx = qatomic_read(&co->ctx);
 637
 638     aio_co_enter(ctx, co);
 639 }
 640
 641 void aio_co_enter(AioContext *ctx, struct Coroutine *co)
 642 {
 643     if (ctx != qemu_get_current_aio_context()) {
 644         aio_co_schedule(ctx, co);
 645         return;
 646     }
 647
 648     if (qemu_in_coroutine()) {
 649         Coroutine *self = qemu_coroutine_self();
 650         assert(self != co);
 651         QSIMPLEQ_INSERT_TAIL(&self->co_queue_wakeup, co, co_queue_next);
 652     } else {
 653         aio_context_acquire(ctx);
 654         qemu_aio_coroutine_enter(ctx, co);
 655         aio_context_release(ctx);
 656     }
 657 }
 658
 659 void aio_context_ref(AioContext *ctx)
 660 {
 661     g_source_ref(&ctx->source);
 662 }
 663
 664 void aio_context_unref(AioContext *ctx)
 665 {
 666     g_source_unref(&ctx->source);
 667 }
 668
 669 void aio_context_acquire(AioContext *ctx)
 670 {
 671     qemu_rec_mutex_lock(&ctx->lock);
 672 }
 673
 674 void aio_context_release(AioContext *ctx)
 675 {
 676     qemu_rec_mutex_unlock(&ctx->lock);
 677 }
 678
 679 QEMU_DEFINE_STATIC_CO_TLS(AioContext *, my_aiocontext)
 680
 681 AioContext *qemu_get_current_aio_context(void)
 682 {
 683     AioContext *ctx = get_my_aiocontext();
 684     if (ctx) {
 685         return ctx;
 686     }
 687     if (qemu_mutex_iothread_locked()) {
 688         /* Possibly in a vCPU thread.  */
 689         return qemu_get_aio_context();
 690     }
 691     return NULL;
 692 }
 693
 694 void qemu_set_current_aio_context(AioContext *ctx)
 695 {
 696     assert(!get_my_aiocontext());
 697     set_my_aiocontext(ctx);
 698 }