fix qemu_aio_flush

qemu_aio_wait by invoking the bh or one of the aio completion
callbacks, could end up submitting new pending aio, breaking the
invariant that qemu_aio_flush returns only when no pending aio is
outstanding (possibly a problem for migration as such).

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/aio.c b/aio.c
index 11fbb6c0c5..dc9b85d167 100644
--- a/aio.c
+++ b/aio.c
@@ -103,11 +103,15 @@ void qemu_aio_flush(void)
     do {
         ret = 0;
 
+	/*
+	 * If there are pending emulated aio start them now so flush
+	 * will be able to return 1.
+	 */
+        qemu_aio_wait();
+
         LIST_FOREACH(node, &aio_handlers, node) {
             ret |= node->io_flush(node->opaque);
         }
-
-        qemu_aio_wait();
     } while (ret > 0);
 }