A couple of the warnings will be followed by an Oops if they ever fire, so may
as well be BUG_ON.  Another isn't obviously fatal but has never been known to
fire, so make it a WARN_ON.

Cc: Adrian Bunk <bunk@stusta.de>
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>