BugLink: http://bugs.launchpad.net/bugs/1578798

commit 6545b60b upstream.

Commit 9567366f ("dm cache metadata: fix READ_LOCK macros and
cleanup WRITE_LOCK macros") uses down_write() instead of down_read() in
cmd_read_lock(), yet up_read() is used to release the lock in
READ_UNLOCK().  Fix it.

Fixes: 9567366f ("dm cache metadata: fix READ_LOCK macros and cleanup WRITE_LOCK macros")
Signed-off-by: Ahmed Samy <f.fallen45@gmail.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>