Merge tag 'dm-4.2-fixes-5' of git://git.kernel.org/pub/scm/linux/kernel/git/device...

Pull device mapper fixes from Mike Snitzer:

 - two stable fixes for corruption seen in a snapshot of thinp metadata;
   metadata snapshots aren't widely used but help provide a consistent
   view of the metadata associated with an active thin-pool.

 - a dm-cache fix for the 4.2 "default" policy switch from "mq" to "smq"

* tag 'dm-4.2-fixes-5' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm:
  dm cache policy smq: move 'dm-cache-default' module alias to SMQ
  dm btree: add ref counting ops for the leaves of top level btrees
  dm thin metadata: delete btrees when releasing metadata snapshot