qemu_bh_schedule() is supposed to be thread-safe at least the first time
it is called. Unfortunately this is not quite true:
bh->scheduled = 1;
aio_notify(bh->ctx);
Since another thread may run the BH callback once it has been scheduled,
there is a race condition if the callback frees the BH before
aio_notify(bh->ctx) has a chance to run.
Reported-by: Stefan Priebe <s.pri...@profihost.ag>
Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
---
async.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/async.c b/async.c
index 6930185..5b6fe6b 100644
--- a/async.c
+++ b/async.c
@@ -117,15 +117,21 @@ void qemu_bh_schedule_idle(QEMUBH *bh)
void qemu_bh_schedule(QEMUBH *bh)
{
+ AioContext *ctx;
+
if (bh->scheduled)
return;
+ ctx = bh->ctx;
bh->idle = 0;
- /* Make sure that idle & any writes needed by the callback are done
- * before the locations are read in the aio_bh_poll.
+ /* Make sure that:
+ * 1. idle & any writes needed by the callback are done before the
+ * locations are read in the aio_bh_poll.
+ * 2. ctx is loaded before scheduled is set and the callback has a chance
+ * to execute.
*/
- smp_wmb();
+ smp_mb();
bh->scheduled = 1;
- aio_notify(bh->ctx);
+ aio_notify(ctx);
}
--
1.9.3
