[Xen-changelog] [qemu-xen stable-4.10] block/mirror: check backing in bdrv_mirror_top_flush

[patchbot@xxxxxxx]

commit 49958d37e7fcacb71512c781d21de2bb69e1c16b
Author:     Vladimir Sementsov-Ogievskiy <vsementsov@xxxxxxxxxxxxx>
AuthorDate: Fri Sep 29 18:22:55 2017 +0300
Commit:     Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
CommitDate: Mon Dec 4 20:40:23 2017 -0600

    block/mirror: check backing in bdrv_mirror_top_flush
    
    Backing may be zero after failed bdrv_append in mirror_start_job,
    which leads to SIGSEGV.
    
    Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@xxxxxxxxxxxxx>
    Message-id: 20170929152255.5431-1-vsementsov@xxxxxxxxxxxxx
    Signed-off-by: Max Reitz <mreitz@xxxxxxxxxx>
    (cherry picked from commit ce960aa9062a407d0ca15aee3dcd3bd84a4e24f9)
    Signed-off-by: Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
---
 block/mirror.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/block/mirror.c b/block/mirror.c
index 429751b..03fc6d6 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -1056,6 +1056,10 @@ static int coroutine_fn 
bdrv_mirror_top_pwritev(BlockDriverState *bs,
 
 static int coroutine_fn bdrv_mirror_top_flush(BlockDriverState *bs)
 {
+    if (bs->backing == NULL) {
+        /* we can be here after failed bdrv_append in mirror_start_job */
+        return 0;
+    }
     return bdrv_co_flush(bs->backing->bs);
 }
 
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#stable-4.10

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