Memory barriers and spin_unlock safety

[Matthew Wilcox]

On Tue, Mar 07, 2006 at 05:36:59PM +0000, David Howells wrote:
> David Howells <dhowells at redhat.com> wrote:
> 
> > I suspect, then, that x86_64 should not have an SFENCE for smp_wmb(), and
> > that only io_wmb() should have that.
> 
> Hmmm... We don't actually have io_wmb()... Should the following be added to
> all archs?
> 
> 	io_mb()
> 	io_rmb()
> 	io_wmb()

it's spelled mmiowb(), and reads from IO space are synchronous, so don't
need barriers.