Please add commit a24fa22ce22ae302b3bf8f7008896d52d5d57b8d
("xen/blkback: don't use xen_blkif_get() in xen-blkback kthread")
to the stable tree.
It is removing a resource leak when destroying a xen guest while I/Os
are still running resulting in zombie domains.
Thanks,
Juergen