Re: [RFC PATCH v1 1/5] locking/atomic: Implement atomic_fetch_and_or

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Jul 28, 2021 at 02:58:35PM +0200, Peter Zijlstra wrote:
> Urgh.. please start from something like the below and then run:
> 
>   scripts/atomic/gen-atomics.sh
> 
> The below isn't quite right, because it'll use try_cmpxchg() for
> atomic_andnot_or(), which by being a void atomic should be _relaxed. I'm
> not entirely sure how to make that happen in a hurry.
> 

Of note, the below is on top of tip/locking/core, which includes a bunch
of atomic work from Mark.

> ---
> 
> diff --git a/scripts/atomic/atomics.tbl b/scripts/atomic/atomics.tbl
> index fbee2f6190d9..3aaa0caa6b2d 100755
> --- a/scripts/atomic/atomics.tbl
> +++ b/scripts/atomic/atomics.tbl
> @@ -39,3 +39,4 @@ inc_not_zero		b	v
>  inc_unless_negative	b	v
>  dec_unless_positive	b	v
>  dec_if_positive		i	v
> +andnot_or		vF	v	i:m	i:o
> diff --git a/scripts/atomic/fallbacks/andnot_or b/scripts/atomic/fallbacks/andnot_or
> new file mode 100644
> index 000000000000..f50e78d6c53a
> --- /dev/null
> +++ b/scripts/atomic/fallbacks/andnot_or
> @@ -0,0 +1,15 @@
> +cat <<EOF
> +static __always_inline ${ret}
> +arch_${atomic}_${pfx}andnot_or${sfx}${order}(${atomic}_t *v, ${int} m, ${int} o)
> +{
> +	${retstmt}({
> +		${int} N, O = atomic_read(v);
> +		do {
> +			N = O;
> +			N &= ~m;
> +			N |= o;
> +		} while (!arch_${atomic}_try_cmpxchg${order}(v, &O, N));
> +		O;
> +	});
> +}
> +EOF
> diff --git a/scripts/atomic/fallbacks/fetch_andnot_or b/scripts/atomic/fallbacks/fetch_andnot_or
> deleted file mode 100644
> index e69de29bb2d1..000000000000
>