Memory barriers and spin_unlock safety

[Alan Cox]

On Maw, 2006-03-07 at 19:54 -0800, Linus Torvalds wrote:
> Close, yes. HOWEVER, it's only really ordered wrt the "innermost" bus. I 
> don't think PCI bridges are supposed to post PIO writes, but a x86 CPU 
> basically won't stall for them forever.

The bridges I have will stall forever. You can observe this directly if
an IDE device decides to hang the IORDY line on the IDE cable or you
crash the GPU on an S3 card.

Alan