Re: [PATCH v2 3/5] locking/arch: Wire up local_try_cmpxchg

[Peter Zijlstra]

On Wed, Apr 12, 2023 at 03:37:50PM +0200, Uros Bizjak wrote:
> On Wed, Apr 12, 2023 at 1:33 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> >
> > On Wed, Apr 05, 2023 at 04:17:08PM +0200, Uros Bizjak wrote:
> > > diff --git a/arch/powerpc/include/asm/local.h b/arch/powerpc/include/asm/local.h
> > > index bc4bd19b7fc2..45492fb5bf22 100644
> > > --- a/arch/powerpc/include/asm/local.h
> > > +++ b/arch/powerpc/include/asm/local.h
> > > @@ -90,6 +90,17 @@ static __inline__ long local_cmpxchg(local_t *l, long o, long n)
> > >       return t;
> > >  }
> > >
> > > +static __inline__ bool local_try_cmpxchg(local_t *l, long *po, long n)
> > > +{
> > > +     long o = *po, r;
> > > +
> > > +     r = local_cmpxchg(l, o, n);
> > > +     if (unlikely(r != o))
> > > +             *po = r;
> > > +
> > > +     return likely(r == o);
> > > +}
> > > +
> >
> > Why is the ppc one different from the rest? Why can't it use the
> > try_cmpxchg_local() fallback and needs to have it open-coded?
> 
> Please note that ppc directly defines local_cmpxchg that bypasses
> cmpxchg_local/arch_cmpxchg_local machinery. The patch takes the same
> approach for local_try_cmpxchg, because fallbacks are using
> arch_cmpxchg_local definitions.
> 
> PPC should be converted to use arch_cmpxchg_local (to also enable
> instrumentation), but this is not the scope of the proposed patchset.

Ah indeed. Thanks!