diff options
Diffstat (limited to 'util/aio-win32.c')
| -rw-r--r-- | util/aio-win32.c | 17 |
1 files changed, 14 insertions, 3 deletions
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); } |