From: Scott Wood <firstname.lastname@example.org>
Date: Tue, 20 May 2008 17:35:56 -0500
The __volatile__ in the asm construct disallows movement of the
inline asm relative to statements surrounding it.
The only reason barrier() in kernel.h needs a memory clobber is
because of a bug in ancient versions of gcc. In fact, I think
that memory clobber might even be removable.