@@ -514,7 +514,12 @@ static void mirror_exit(BlockJob *job, void *opaque)
/* Remove target parent that still uses BLK_PERM_WRITE/RESIZE before
* inserting target_bs at s->to_replace, where we might not be able to get
- * these permissions. */
+ * these permissions.
+ *
+ * Note that blk_unref() alone doesn't necessarily drop permissions because
+ * we might be running nested inside mirror_drain(), which takes an extra
+ * reference, so use an explicit blk_set_perm() first. */
+ blk_set_perm(s->target, 0, BLK_PERM_ALL, &error_abort);
blk_unref(s->target);
s->target = NULL;
This fixes an assertion failure that was triggered by qemu-iotests 129 on some CI host, while the same test case didn't seem to fail on other hosts. Essentially the problem is that the blk_unref(s->target) in mirror_exit() doesn't necessarily mean that the BlockBackend goes away immediately. It is possible that the job completion was triggered nested in mirror_drain(), which looks like this: BlockBackend *target = s->target; blk_ref(target); blk_drain(target); blk_unref(target); In this case, the write permissions for s->target are retained until after blk_drain(), which makes removing mirror_top_bs fail for the active commit case (can't have a writable backing file in the chain without the filter driver). Explicitly dropping the permissions first means that the additional reference doesn't hurt and the job can complete successfully even if called from the nested blk_drain(). Cc: qemu-stable@nongnu.org Signed-off-by: Kevin Wolf <kwolf@redhat.com> Acked-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com> --- block/mirror.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)