bdrv_attach_child() do bdrv_unref() on failure, so we shouldn't do it
by hand here.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
---
 block/copy-before-write.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/block/copy-before-write.c b/block/copy-before-write.c
index 2a51cc64e4..945d9340f4 100644
--- a/block/copy-before-write.c
+++ b/block/copy-before-write.c
@@ -201,7 +201,6 @@ BlockDriverState *bdrv_cbw_append(BlockDriverState *source,
     state->target = bdrv_attach_child(top, target, "target", &child_of_bds,
                                       BDRV_CHILD_DATA, errp);
     if (!state->target) {
-        bdrv_unref(target);
         bdrv_unref(top);
         return NULL;
     }
-- 
2.29.2