[PATCH] Document Linux's memory barriers

[Bryan O'Sullivan]

On Tue, 2006-03-07 at 12:57 +0100, Andi Kleen wrote:

> > > True, I suppose. I should make it clear that these accessor functions imply
> > > memory barriers, if indeed they do,
> > 
> > They don't, but according to Documentation/DocBook/deviceiobook.tmpl
> > they are performed by the compiler in the order specified.
> 
> I don't think that's correct. Probably the documentation should
> be fixed.

That's why I hedged my words with "according to ..." :-)

But on most arches those accesses do indeed seem to happen in-order.  On
i386 and x86_64, it's a natural consequence of program store ordering.
On at least some other arches, there are explicit memory barriers in the
implementation of the access macros to force this ordering to occur.

	<b