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 "block/raw-aio.h"
  33 #include "qemu/coroutine_int.h"
  34 #include "trace.h"
  35
  36 /***********************************************************/
  37 /* bottom halves (can be seen as timers which expire ASAP) */
  38
  39 struct QEMUBH {
  40     AioContext *ctx;
  41     QEMUBHFunc *cb;
  42     void *opaque;
  43     QEMUBH *next;
  44     bool scheduled;
  45     bool idle;
  46     bool deleted;
  47 };
  48
  49 void aio_bh_schedule_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
  50 {
  51     QEMUBH *bh;
  52     bh = g_new(QEMUBH, 1);
  53     *bh = (QEMUBH){
  54         .ctx = ctx,
  55         .cb = cb,
  56         .opaque = opaque,
  57     };
  58     qemu_lockcnt_lock(&ctx->list_lock);
  59     bh->next = ctx->first_bh;
  60     bh->scheduled = 1;
  61     bh->deleted = 1;
  62     /* Make sure that the members are ready before putting bh into list */
  63     smp_wmb();
  64     ctx->first_bh = bh;
  65     qemu_lockcnt_unlock(&ctx->list_lock);
  66     aio_notify(ctx);
  67 }
  68
  69 QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
  70 {
  71     QEMUBH *bh;
  72     bh = g_new(QEMUBH, 1);
  73     *bh = (QEMUBH){
  74         .ctx = ctx,
  75         .cb = cb,
  76         .opaque = opaque,
  77     };
  78     qemu_lockcnt_lock(&ctx->list_lock);
  79     bh->next = ctx->first_bh;
  80     /* Make sure that the members are ready before putting bh into list */
  81     smp_wmb();
  82     ctx->first_bh = bh;
  83     qemu_lockcnt_unlock(&ctx->list_lock);
  84     return bh;
  85 }
  86
  87 void aio_bh_call(QEMUBH *bh)
  88 {
  89     bh->cb(bh->opaque);
  90 }
  91
  92 /* Multiple occurrences of aio_bh_poll cannot be called concurrently.
  93  * The count in ctx->list_lock is incremented before the call, and is
  94  * not affected by the call.
  95  */
  96 int aio_bh_poll(AioContext *ctx)
  97 {
  98     QEMUBH *bh, **bhp, *next;
  99     int ret;
 100     bool deleted = false;
 101
 102     ret = 0;
 103     for (bh = atomic_rcu_read(&ctx->first_bh); bh; bh = next) {
 104         next = atomic_rcu_read(&bh->next);
 105         /* The atomic_xchg is paired with the one in qemu_bh_schedule.  The
 106          * implicit memory barrier ensures that the callback sees all writes
 107          * done by the scheduling thread.  It also ensures that the scheduling
 108          * thread sees the zero before bh->cb has run, and thus will call
 109          * aio_notify again if necessary.
 110          */
 111         if (atomic_xchg(&bh->scheduled, 0)) {
 112             /* Idle BHs don't count as progress */
 113             if (!bh->idle) {
 114                 ret = 1;
 115             }
 116             bh->idle = 0;
 117             aio_bh_call(bh);
 118         }
 119         if (bh->deleted) {
 120             deleted = true;
 121         }
 122     }
 123
 124     /* remove deleted bhs */
 125     if (!deleted) {
 126         return ret;
 127     }
 128
 129     if (qemu_lockcnt_dec_if_lock(&ctx->list_lock)) {
 130         bhp = &ctx->first_bh;
 131         while (*bhp) {
 132             bh = *bhp;
 133             if (bh->deleted && !bh->scheduled) {
 134                 *bhp = bh->next;
 135                 g_free(bh);
 136             } else {
 137                 bhp = &bh->next;
 138             }
 139         }
 140         qemu_lockcnt_inc_and_unlock(&ctx->list_lock);
 141     }
 142     return ret;
 143 }
 144
 145 void qemu_bh_schedule_idle(QEMUBH *bh)
 146 {
 147     bh->idle = 1;
 148     /* Make sure that idle & any writes needed by the callback are done
 149      * before the locations are read in the aio_bh_poll.
 150      */
 151     atomic_mb_set(&bh->scheduled, 1);
 152 }
 153
 154 void qemu_bh_schedule(QEMUBH *bh)
 155 {
 156     AioContext *ctx;
 157
 158     ctx = bh->ctx;
 159     bh->idle = 0;
 160     /* The memory barrier implicit in atomic_xchg makes sure that:
 161      * 1. idle & any writes needed by the callback are done before the
 162      *    locations are read in the aio_bh_poll.
 163      * 2. ctx is loaded before scheduled is set and the callback has a chance
 164      *    to execute.
 165      */
 166     if (atomic_xchg(&bh->scheduled, 1) == 0) {
 167         aio_notify(ctx);
 168     }
 169 }
 170
 171
 172 /* This func is async.
 173  */
 174 void qemu_bh_cancel(QEMUBH *bh)
 175 {
 176     atomic_mb_set(&bh->scheduled, 0);
 177 }
 178
 179 /* This func is async.The bottom half will do the delete action at the finial
 180  * end.
 181  */
 182 void qemu_bh_delete(QEMUBH *bh)
 183 {
 184     bh->scheduled = 0;
 185     bh->deleted = 1;
 186 }
 187
 188 int64_t
 189 aio_compute_timeout(AioContext *ctx)
 190 {
 191     int64_t deadline;
 192     int timeout = -1;
 193     QEMUBH *bh;
 194
 195     for (bh = atomic_rcu_read(&ctx->first_bh); bh;
 196          bh = atomic_rcu_read(&bh->next)) {
 197         if (bh->scheduled) {
 198             if (bh->idle) {
 199                 /* idle bottom halves will be polled at least
 200                  * every 10ms */
 201                 timeout = 10000000;
 202             } else {
 203                 /* non-idle bottom halves will be executed
 204                  * immediately */
 205                 return 0;
 206             }
 207         }
 208     }
 209
 210     deadline = timerlistgroup_deadline_ns(&ctx->tlg);
 211     if (deadline == 0) {
 212         return 0;
 213     } else {
 214         return qemu_soonest_timeout(timeout, deadline);
 215     }
 216 }
 217
 218 static gboolean
 219 aio_ctx_prepare(GSource *source, gint    *timeout)
 220 {
 221     AioContext *ctx = (AioContext *) source;
 222
 223     atomic_or(&ctx->notify_me, 1);
 224
 225     /* We assume there is no timeout already supplied */
 226     *timeout = qemu_timeout_ns_to_ms(aio_compute_timeout(ctx));
 227
 228     if (aio_prepare(ctx)) {
 229         *timeout = 0;
 230     }
 231
 232     return *timeout == 0;
 233 }
 234
 235 static gboolean
 236 aio_ctx_check(GSource *source)
 237 {
 238     AioContext *ctx = (AioContext *) source;
 239     QEMUBH *bh;
 240
 241     atomic_and(&ctx->notify_me, ~1);
 242     aio_notify_accept(ctx);
 243
 244     for (bh = ctx->first_bh; bh; bh = bh->next) {
 245         if (bh->scheduled) {
 246             return true;
 247         }
 248     }
 249     return aio_pending(ctx) || (timerlistgroup_deadline_ns(&ctx->tlg) == 0);
 250 }
 251
 252 static gboolean
 253 aio_ctx_dispatch(GSource     *source,
 254                  GSourceFunc  callback,
 255                  gpointer     user_data)
 256 {
 257     AioContext *ctx = (AioContext *) source;
 258
 259     assert(callback == NULL);
 260     aio_dispatch(ctx);
 261     return true;
 262 }
 263
 264 static void
 265 aio_ctx_finalize(GSource     *source)
 266 {
 267     AioContext *ctx = (AioContext *) source;
 268
 269     thread_pool_free(ctx->thread_pool);
 270
 271 #ifdef CONFIG_LINUX_AIO
 272     if (ctx->linux_aio) {
 273         laio_detach_aio_context(ctx->linux_aio, ctx);
 274         laio_cleanup(ctx->linux_aio);
 275         ctx->linux_aio = NULL;
 276     }
 277 #endif
 278
 279     assert(QSLIST_EMPTY(&ctx->scheduled_coroutines));
 280     qemu_bh_delete(ctx->co_schedule_bh);
 281
 282     qemu_lockcnt_lock(&ctx->list_lock);
 283     assert(!qemu_lockcnt_count(&ctx->list_lock));
 284     while (ctx->first_bh) {
 285         QEMUBH *next = ctx->first_bh->next;
 286
 287         /* qemu_bh_delete() must have been called on BHs in this AioContext */
 288         assert(ctx->first_bh->deleted);
 289
 290         g_free(ctx->first_bh);
 291         ctx->first_bh = next;
 292     }
 293     qemu_lockcnt_unlock(&ctx->list_lock);
 294
 295     aio_set_event_notifier(ctx, &ctx->notifier, false, NULL, NULL);
 296     event_notifier_cleanup(&ctx->notifier);
 297     qemu_rec_mutex_destroy(&ctx->lock);
 298     qemu_lockcnt_destroy(&ctx->list_lock);
 299     timerlistgroup_deinit(&ctx->tlg);
 300     aio_context_destroy(ctx);
 301 }
 302
 303 static GSourceFuncs aio_source_funcs = {
 304     aio_ctx_prepare,
 305     aio_ctx_check,
 306     aio_ctx_dispatch,
 307     aio_ctx_finalize
 308 };
 309
 310 GSource *aio_get_g_source(AioContext *ctx)
 311 {
 312     g_source_ref(&ctx->source);
 313     return &ctx->source;
 314 }
 315
 316 ThreadPool *aio_get_thread_pool(AioContext *ctx)
 317 {
 318     if (!ctx->thread_pool) {
 319         ctx->thread_pool = thread_pool_new(ctx);
 320     }
 321     return ctx->thread_pool;
 322 }
 323
 324 #ifdef CONFIG_LINUX_AIO
 325 LinuxAioState *aio_setup_linux_aio(AioContext *ctx, Error **errp)
 326 {
 327     if (!ctx->linux_aio) {
 328         ctx->linux_aio = laio_init(errp);
 329         if (ctx->linux_aio) {
 330             laio_attach_aio_context(ctx->linux_aio, ctx);
 331         }
 332     }
 333     return ctx->linux_aio;
 334 }
 335
 336 LinuxAioState *aio_get_linux_aio(AioContext *ctx)
 337 {
 338     assert(ctx->linux_aio);
 339     return ctx->linux_aio;
 340 }
 341 #endif
 342
 343 void aio_notify(AioContext *ctx)
 344 {
 345     /* Write e.g. bh->scheduled before reading ctx->notify_me.  Pairs
 346      * with atomic_or in aio_ctx_prepare or atomic_add in aio_poll.
 347      */
 348     smp_mb();
 349     if (ctx->notify_me) {
 350         event_notifier_set(&ctx->notifier);
 351         atomic_mb_set(&ctx->notified, true);
 352     }
 353 }
 354
 355 void aio_notify_accept(AioContext *ctx)
 356 {
 357     if (atomic_xchg(&ctx->notified, false)) {
 358         event_notifier_test_and_clear(&ctx->notifier);
 359     }
 360 }
 361
 362 static void aio_timerlist_notify(void *opaque, QEMUClockType type)
 363 {
 364     aio_notify(opaque);
 365 }
 366
 367 static void event_notifier_dummy_cb(EventNotifier *e)
 368 {
 369 }
 370
 371 /* Returns true if aio_notify() was called (e.g. a BH was scheduled) */
 372 static bool event_notifier_poll(void *opaque)
 373 {
 374     EventNotifier *e = opaque;
 375     AioContext *ctx = container_of(e, AioContext, notifier);
 376
 377     return atomic_read(&ctx->notified);
 378 }
 379
 380 static void co_schedule_bh_cb(void *opaque)
 381 {
 382     AioContext *ctx = opaque;
 383     QSLIST_HEAD(, Coroutine) straight, reversed;
 384
 385     QSLIST_MOVE_ATOMIC(&reversed, &ctx->scheduled_coroutines);
 386     QSLIST_INIT(&straight);
 387
 388     while (!QSLIST_EMPTY(&reversed)) {
 389         Coroutine *co = QSLIST_FIRST(&reversed);
 390         QSLIST_REMOVE_HEAD(&reversed, co_scheduled_next);
 391         QSLIST_INSERT_HEAD(&straight, co, co_scheduled_next);
 392     }
 393
 394     while (!QSLIST_EMPTY(&straight)) {
 395         Coroutine *co = QSLIST_FIRST(&straight);
 396         QSLIST_REMOVE_HEAD(&straight, co_scheduled_next);
 397         trace_aio_co_schedule_bh_cb(ctx, co);
 398         aio_context_acquire(ctx);
 399
 400         /* Protected by write barrier in qemu_aio_coroutine_enter */
 401         atomic_set(&co->scheduled, NULL);
 402         qemu_aio_coroutine_enter(ctx, co);
 403         aio_context_release(ctx);
 404     }
 405 }
 406
 407 AioContext *aio_context_new(Error **errp)
 408 {
 409     int ret;
 410     AioContext *ctx;
 411
 412     ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
 413     aio_context_setup(ctx);
 414
 415     ret = event_notifier_init(&ctx->notifier, false);
 416     if (ret < 0) {
 417         error_setg_errno(errp, -ret, "Failed to initialize event notifier");
 418         goto fail;
 419     }
 420     g_source_set_can_recurse(&ctx->source, true);
 421     qemu_lockcnt_init(&ctx->list_lock);
 422
 423     ctx->co_schedule_bh = aio_bh_new(ctx, co_schedule_bh_cb, ctx);
 424     QSLIST_INIT(&ctx->scheduled_coroutines);
 425
 426     aio_set_event_notifier(ctx, &ctx->notifier,
 427                            false,
 428                            (EventNotifierHandler *)
 429                            event_notifier_dummy_cb,
 430                            event_notifier_poll);
 431 #ifdef CONFIG_LINUX_AIO
 432     ctx->linux_aio = NULL;
 433 #endif
 434     ctx->thread_pool = NULL;
 435     qemu_rec_mutex_init(&ctx->lock);
 436     timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx);
 437
 438     ctx->poll_ns = 0;
 439     ctx->poll_max_ns = 0;
 440     ctx->poll_grow = 0;
 441     ctx->poll_shrink = 0;
 442
 443     return ctx;
 444 fail:
 445     g_source_destroy(&ctx->source);
 446     return NULL;
 447 }
 448
 449 void aio_co_schedule(AioContext *ctx, Coroutine *co)
 450 {
 451     trace_aio_co_schedule(ctx, co);
 452     const char *scheduled = atomic_cmpxchg(&co->scheduled, NULL,
 453                                            __func__);
 454
 455     if (scheduled) {
 456         fprintf(stderr,
 457                 "%s: Co-routine was already scheduled in '%s'\n",
 458                 __func__, scheduled);
 459         abort();
 460     }
 461
 462     /* The coroutine might run and release the last ctx reference before we
 463      * invoke qemu_bh_schedule().  Take a reference to keep ctx alive until
 464      * we're done.
 465      */
 466     aio_context_ref(ctx);
 467
 468     QSLIST_INSERT_HEAD_ATOMIC(&ctx->scheduled_coroutines,
 469                               co, co_scheduled_next);
 470     qemu_bh_schedule(ctx->co_schedule_bh);
 471
 472     aio_context_unref(ctx);
 473 }
 474
 475 void aio_co_wake(struct Coroutine *co)
 476 {
 477     AioContext *ctx;
 478
 479     /* Read coroutine before co->ctx.  Matches smp_wmb in
 480      * qemu_coroutine_enter.
 481      */
 482     smp_read_barrier_depends();
 483     ctx = atomic_read(&co->ctx);
 484
 485     aio_co_enter(ctx, co);
 486 }
 487
 488 void aio_co_enter(AioContext *ctx, struct Coroutine *co)
 489 {
 490     if (ctx != qemu_get_current_aio_context()) {
 491         aio_co_schedule(ctx, co);
 492         return;
 493     }
 494
 495     if (qemu_in_coroutine()) {
 496         Coroutine *self = qemu_coroutine_self();
 497         assert(self != co);
 498         QSIMPLEQ_INSERT_TAIL(&self->co_queue_wakeup, co, co_queue_next);
 499     } else {
 500         aio_context_acquire(ctx);
 501         qemu_aio_coroutine_enter(ctx, co);
 502         aio_context_release(ctx);
 503     }
 504 }
 505
 506 void aio_context_ref(AioContext *ctx)
 507 {
 508     g_source_ref(&ctx->source);
 509 }
 510
 511 void aio_context_unref(AioContext *ctx)
 512 {
 513     g_source_unref(&ctx->source);
 514 }
 515
 516 void aio_context_acquire(AioContext *ctx)
 517 {
 518     qemu_rec_mutex_lock(&ctx->lock);
 519 }
 520
 521 void aio_context_release(AioContext *ctx)
 522 {
 523     qemu_rec_mutex_unlock(&ctx->lock);
 524 }