[PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE()

Peter Zijlstra
Fri, 25 Nov 2016 16:17:09 -0000

On Fri, Nov 25, 2016 at 04:10:04PM +0000, Mark Rutland
wrote:
> On Fri, Nov 25, 2016 at 04:21:39PM +0100, Dmitry Vyukov wrote:

> > What are use cases for such primitive that won't be OK with
"read once
> > _and_ atomically"?
>
> I have none to hand.

Whatever triggers the __builtin_memcpy() paths, and even the size==8
paths on 32bit.

You could put a WARN in there to easily find them.

The advantage of introducing the SINGLE_{LOAD,STORE}() helpers is that
they compiletime validate this the size is 'right' and can runtime check
alignment constraints.

IE, they are strictly stronger than {READ,WRITE}_ONCE().