[PATCH] memory ordering in __kfifo primitives

Both __kfifo_put() and __kfifo_get() have header comments stating that if
there is but one concurrent reader and one concurrent writer, locking is not
necessary.  This is almost the case, but a couple of memory barriers are
needed.  Another option would be to change the header comments to remove the
bit about locking not being needed, and to change the those callers who
currently don't use locking to add the required locking.  The attachment
analyzes this approach, but the patch below seems simpler.

Signed-off-by: Paul E. McKenney <paulmck@us.ibm.com>
Cc: Stelian Pop <stelian@popies.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>