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authorStefan Hajnoczi <stefanha@redhat.com>2014-06-03 11:21:01 +0200
committerStefan Hajnoczi <stefanha@redhat.com>2014-06-04 09:56:06 +0200
commit924fe1293c3e7a3c787bbdfb351e7f168caee3e9 (patch)
tree07e385b640afa86d2a411a2195e3a34bb5b52b91 /async.c
parente00fcfeab3d452cba3d0a08991a39ab15df66424 (diff)
downloadqemu-arm-924fe1293c3e7a3c787bbdfb351e7f168caee3e9.tar.gz
aio: fix qemu_bh_schedule() bh->ctx race condition
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.priebe@profihost.ag> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com> Tested-by: Stefan Priebe <s.priebe@profihost.ag>
Diffstat (limited to 'async.c')
-rw-r--r--async.c14
1 files changed, 10 insertions, 4 deletions
diff --git a/async.c b/async.c
index 6930185e64..5b6fe6b4cc 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);
}