1 files changed, 18 insertions, 1 deletions
diff --git a/async.c b/async.c
index 5b6fe6b4cc..34af0b25ca 100644
--- a/async.c
+++ b/async.c
@@ -26,6 +26,7 @@
 #include "block/aio.h"
 #include "block/thread-pool.h"
 #include "qemu/main-loop.h"
+#include "qemu/atomic.h"
 
 /***********************************************************/
 /* bottom halves (can be seen as timers which expire ASAP) */
@@ -247,9 +248,25 @@ ThreadPool *aio_get_thread_pool(AioContext *ctx)
     return ctx->thread_pool;
 }
 
+void aio_set_dispatching(AioContext *ctx, bool dispatching)
+{
+    ctx->dispatching = dispatching;
+    if (!dispatching) {
+        /* Write ctx->dispatching before reading e.g. bh->scheduled.
+         * Optimization: this is only needed when we're entering the "unsafe"
+         * phase where other threads must call event_notifier_set.
+         */
+        smp_mb();
+    }
+}
+
 void aio_notify(AioContext *ctx)
 {
-    event_notifier_set(&ctx->notifier);
+    /* Write e.g. bh->scheduled before reading ctx->dispatching.  */
+    smp_mb();
+    if (!ctx->dispatching) {
+        event_notifier_set(&ctx->notifier);
+    }
 }
 
 static void aio_timerlist_notify(void *opaque)