[qemu-xen staging-4.13] mirror: Keep mirror_top_bs drained after dropping permissions

[patchbot@xxxxxxx]

commit e092a17d3825a8f2c93cb429aaa5d857b579b64c
Author:     Kevin Wolf <kwolf@xxxxxxxxxx>
AuthorDate: Mon Jul 22 17:44:27 2019 +0200
Commit:     Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
CommitDate: Tue Nov 12 16:31:49 2019 -0600

    mirror: Keep mirror_top_bs drained after dropping permissions
    
    mirror_top_bs is currently implicitly drained through its connection to
    the source or the target node. However, the drain section for target_bs
    ends early after moving mirror_top_bs from src to target_bs, so that
    requests can already be restarted while mirror_top_bs is still present
    in the chain, but has dropped all permissions and therefore runs into an
    assertion failure like this:
    
        qemu-system-x86_64: block/io.c:1634: bdrv_co_write_req_prepare:
        Assertion `child->perm & BLK_PERM_WRITE' failed.
    
    Keep mirror_top_bs drained until all graph changes have completed.
    
    Cc: qemu-stable@xxxxxxxxxx
    Signed-off-by: Kevin Wolf <kwolf@xxxxxxxxxx>
    Reviewed-by: Max Reitz <mreitz@xxxxxxxxxx>
    (cherry picked from commit d2da5e288a2e71e82866c8fdefd41b5727300124)
    Signed-off-by: Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
---
 block/mirror.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/block/mirror.c b/block/mirror.c
index 0e3f7923cf..681b305de6 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -661,7 +661,10 @@ static int mirror_exit_common(Job *job)
     s->target = NULL;
 
     /* We don't access the source any more. Dropping any WRITE/RESIZE is
-     * required before it could become a backing file of target_bs. */
+     * required before it could become a backing file of target_bs. Not having
+     * these permissions any more means that we can't allow any new requests on
+     * mirror_top_bs from now on, so keep it drained. */
+    bdrv_drained_begin(mirror_top_bs);
     bs_opaque->stop = true;
     bdrv_child_refresh_perms(mirror_top_bs, mirror_top_bs->backing,
                              &error_abort);
@@ -729,6 +732,7 @@ static int mirror_exit_common(Job *job)
     bs_opaque->job = NULL;
 
     bdrv_drained_end(src);
+    bdrv_drained_end(mirror_top_bs);
     s->in_drain = false;
     bdrv_unref(mirror_top_bs);
     bdrv_unref(src);
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#staging-4.13