The need for volatile is not obvious, document it.
Signed-off-by: NDavidlohr Bueso <davidlohr@hp.com>
Signed-off-by: NManfred Spraul <manfred@colorfullife.com>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>