[PATCH v9 14/14] powerpc: rewrite local_t using soft_irq

[David Laight]

From: Nicholas Piggin
> Sent: 04 August 2017 10:04
> On Fri, 04 Aug 2017 11:40:43 +1000
> Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote:
> 
> > On Fri, 2017-08-04 at 03:50 +1000, Nicholas Piggin wrote:
> > > Hey, so... why are any of these implemented in asm? We should
> > > just do them all in C, right? I looked a bit harder at code gen
> > > and a couple of them are still emitting larx/stcx.
> >
> > As long as we can guarantee that the C compiler won't play games
> > moving stuff around. But yes, I tend to agree.
> 
> 
> I believe so. I mean we already depend on the same pattern for any
> other sequence of local_irq_disable(); c code; local_irq_enable();
> so we'd have other problems if we couldn't.

I'd guess that a "memory" clobber on the irq_disable/enable would be enough.
It could be restricted to the memory area being updated.

	David