commit 1c751879 upstream.

Allocate memory using GFP_NOIO when deleting a btree.  dm_btree_del()
can be called via an ioctl and we don't want to recurse into the FS or
block layer.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>