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

From: Peter Zijlstra <[email-masked]>
Date: Wed, 12 Apr 2023 13:32:31 +0200

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?