Disk corrupted after snapshot deletion

  I found the vm disk corruption after snapshot deletion sometimes(the probability is very low, I'm afraid i can't reproduce it). And I found there is a patch for it as follow, but I'm not sure whether the patch repaired the bug. 
  Drain disk before snapshot deletion can't guarantee anything, there is still pending IO in snapshot-deletion process. Anyone can help?

author	Zhang Haoyu <email address hidden>	2014-10-21 16:38:01 +0800
committer	Stefan Hajnoczi <email address hidden>	2014-11-03 09:48:42 +0000
commit	3432a1929ee18e08787ce35476abd74f2c93a17c (patch)
tree	13a81c0a46707d91622f1593ccf7b926935371fd /block/snapshot.c
parent	573742a5431a99ceaba6968ae269cee247727cce (diff)
snapshot: add bdrv_drain_all() to bdrv_snapshot_delete() to avoid concurrency problem
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 <email address hidden>
Reviewed-by: Paolo Bonzini <email address hidden>
Message-id: <email address hidden>
Signed-off-by: Stefan Hajnoczi <email address hidden>
Diffstat (limited to 'block/snapshot.c')
-rw-r--r--	block/snapshot.c	4	
1 files changed, 4 insertions, 0 deletions
diff --git a/block/snapshot.c b/block/snapshot.c
index 85c52ff..698e1a1 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);
     }