diff options
| -rw-r--r-- | util/aio-posix.c | 16 | ||||
| -rw-r--r-- | util/aio-win32.c | 17 | ||||
| -rw-r--r-- | util/async.c | 16 |
3 files changed, 40 insertions, 9 deletions
diff --git a/util/aio-posix.c b/util/aio-posix.c index cd6cf0a4a9..c3613d299e 100644 --- a/util/aio-posix.c +++ b/util/aio-posix.c @@ -559,6 +559,11 @@ bool aio_poll(AioContext *ctx, bool blocking) int64_t timeout; int64_t start = 0; + /* + * There cannot be two concurrent aio_poll calls for the same AioContext (or + * an aio_poll concurrent with a GSource prepare/check/dispatch callback). + * We rely on this below to avoid slow locked accesses to ctx->notify_me. + */ assert(in_aio_context_home_thread(ctx)); /* aio_notify can avoid the expensive event_notifier_set if @@ -569,7 +574,13 @@ bool aio_poll(AioContext *ctx, bool blocking) * so disable the optimization now. */ if (blocking) { - atomic_add(&ctx->notify_me, 2); + atomic_set(&ctx->notify_me, atomic_read(&ctx->notify_me) + 2); + /* + * Write ctx->notify_me before computing the timeout + * (reading bottom half flags, etc.). Pairs with + * smp_mb in aio_notify(). + */ + smp_mb(); } qemu_lockcnt_inc(&ctx->list_lock); @@ -590,7 +601,8 @@ bool aio_poll(AioContext *ctx, bool blocking) } if (blocking) { - atomic_sub(&ctx->notify_me, 2); + /* Finish the poll before clearing the flag. */ + atomic_store_release(&ctx->notify_me, atomic_read(&ctx->notify_me) - 2); aio_notify_accept(ctx); } diff --git a/util/aio-win32.c b/util/aio-win32.c index a23b9c364d..729d533faf 100644 --- a/util/aio-win32.c +++ b/util/aio-win32.c @@ -321,6 +321,12 @@ bool aio_poll(AioContext *ctx, bool blocking) int count; int timeout; + /* + * There cannot be two concurrent aio_poll calls for the same AioContext (or + * an aio_poll concurrent with a GSource prepare/check/dispatch callback). + * We rely on this below to avoid slow locked accesses to ctx->notify_me. + */ + assert(in_aio_context_home_thread(ctx)); progress = false; /* aio_notify can avoid the expensive event_notifier_set if @@ -331,7 +337,13 @@ bool aio_poll(AioContext *ctx, bool blocking) * so disable the optimization now. */ if (blocking) { - atomic_add(&ctx->notify_me, 2); + atomic_set(&ctx->notify_me, atomic_read(&ctx->notify_me) + 2); + /* + * Write ctx->notify_me before computing the timeout + * (reading bottom half flags, etc.). Pairs with + * smp_mb in aio_notify(). + */ + smp_mb(); } qemu_lockcnt_inc(&ctx->list_lock); @@ -364,8 +376,7 @@ bool aio_poll(AioContext *ctx, bool blocking) ret = WaitForMultipleObjects(count, events, FALSE, timeout); if (blocking) { assert(first); - assert(in_aio_context_home_thread(ctx)); - atomic_sub(&ctx->notify_me, 2); + atomic_store_release(&ctx->notify_me, atomic_read(&ctx->notify_me) - 2); aio_notify_accept(ctx); } diff --git a/util/async.c b/util/async.c index b94518b948..3165a28f2f 100644 --- a/util/async.c +++ b/util/async.c @@ -249,7 +249,14 @@ aio_ctx_prepare(GSource *source, gint *timeout) { AioContext *ctx = (AioContext *) source; - atomic_or(&ctx->notify_me, 1); + atomic_set(&ctx->notify_me, atomic_read(&ctx->notify_me) | 1); + + /* + * Write ctx->notify_me before computing the timeout + * (reading bottom half flags, etc.). Pairs with + * smp_mb in aio_notify(). + */ + smp_mb(); /* We assume there is no timeout already supplied */ *timeout = qemu_timeout_ns_to_ms(aio_compute_timeout(ctx)); @@ -268,7 +275,8 @@ aio_ctx_check(GSource *source) QEMUBH *bh; BHListSlice *s; - atomic_and(&ctx->notify_me, ~1); + /* Finish computing the timeout before clearing the flag. */ + atomic_store_release(&ctx->notify_me, atomic_read(&ctx->notify_me) & ~1); aio_notify_accept(ctx); QSLIST_FOREACH_RCU(bh, &ctx->bh_list, next) { @@ -411,10 +419,10 @@ LuringState *aio_get_linux_io_uring(AioContext *ctx) void aio_notify(AioContext *ctx) { /* Write e.g. bh->scheduled before reading ctx->notify_me. Pairs - * with atomic_or in aio_ctx_prepare or atomic_add in aio_poll. + * with smp_mb in aio_ctx_prepare or aio_poll. */ smp_mb(); - if (ctx->notify_me) { + if (atomic_read(&ctx->notify_me)) { event_notifier_set(&ctx->notifier); atomic_mb_set(&ctx->notified, true); } |