Pull device mapper fixes from Mike Snitzer:

 - stable fix for dm-thin that avoids normal IO racing with discard

 - stable fix for a dm-cache related bug in dm-btree walking code that
   results from using very large fast device (eg 4T) with a very small
   cache blocksize (eg 32K) -- this is a very uncommon configuration

 - a couple fixes for dm-raid (one for stable and the other addresses a
   crash in 3.18-rc1 code)

 - stable fix for dm-thinp that addresses a very rare dm-bufio bug
   having to do with memory reclaimation (via shrinker) when using
   dm-thinp ontop of loopback devices

 - fix a leak in dm-stripe target constructor's error path

* tag 'dm-3.18-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm:
  dm btree: fix a recursion depth bug in btree walking code
  dm thin: grab a virtual cell before looking up the mapping
  dm raid: fix inaccessible superblocks causing oops in configure_discard_support
  dm raid: ensure superblock's size matches device's logical block size
  dm bufio: change __GFP_IO to __GFP_FS in shrinker callbacks
  dm stripe: fix potential for leak in stripe_ctr error path