[PATCH] Document Linux's memory barriers [try #2]

[Paul Mackerras]

Jesse Barnes writes:

> It uses a per-node address space to reference the local bridge.  The 
> local bridge then waits until the remote bridge has acked the write 
> before, then sets the outstanding write register to the appropriate 
> value.

That sounds like mmiowb can only be used when preemption is disabled,
such as inside a spin-locked region - is that right?

Paul.