[Qemu-devel] [PATCH bugfix] snapshot: add bdrv_drain_all() to bdrv_snapshot_delete() to avoid concurrency problem

["Zhang Haoyu" <zhanghy@sangfor.com>]

If there are still pending i/o while deleting snapshot,
because deleting snapshot is done in non-coroutine context, and
the pending i/o read/write (bdrv_co_do_rw) is done in coroutine context,
so it's possible to cause concurrency problem between above two operations.
Add bdrv_drain_all() to bdrv_snapshot_delete() to avoid this problem.

Signed-off-by: Zhang Haoyu <zhanghy@sangfor.com>
---
 block/snapshot.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/block/snapshot.c b/block/snapshot.c
index 85c52ff..ebc386a 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -236,6 +236,10 @@ int bdrv_snapshot_delete(BlockDriverState *bs,
         error_setg(errp, "snapshot_id and name are both NULL");
         return -EINVAL;
     }
+
+    /* drain all pending i/o before deleting snapshot */
+    bdrv_drain_all();
+
     if (drv->bdrv_snapshot_delete) {
         return drv->bdrv_snapshot_delete(bs, snapshot_id, name, errp);
     }
-- 
1.7.12.4