On Mon, Jan 04, 2016 at 02:36:58PM +0100, Peter Zijlstra wrote:

On Sun, Jan 03, 2016 at 11:12:44AM +0200, Michael S. Tsirkin wrote:

quoted

On Sat, Jan 02, 2016 at 11:24:38AM +0000, Russell King - ARM Linux wrote:

quoted

quoted

My only concern is that it gives people an additional handle onto a
"new" set of barriers - just because they're prefixed with __*
unfortunately doesn't stop anyone from using it (been there with
other arch stuff before.)

I wonder whether we should consider making the smp memory barriers
inline functions, so these __smp_xxx() variants can be undef'd
afterwards, thereby preventing drivers getting their hands on these
new macros?

That'd be tricky to do cleanly since asm-generic depends on
ifndef to add generic variants where needed.

But it would be possible to add a checkpatch test for this.

Wasn't the whole purpose of these things for 'drivers' (namely
virtio/xen hypervisor interaction) to use these?

My take out from discussion with you was that virtualization is probably
the only valid use-case.  So at David Miller's suggestion there's a
patch later in the series that adds virt_xxxx wrappers and these are
then used by virtio xen and later maybe others.

And I suppose most of virtio would actually be modules, so you cannot do
what I did with preempt_enable_no_resched() either.

But yes, it would be good to limit the use of these things.

Right so the trick is checkpatch warns about use of
__smp_xxx and hopefully people are not crazy enough
to use virt_xxx variants for non-virtual drivers.

-- 
MST