linux-kernel - Re: [PATCH] asm-generic/atomic: Add try

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Message-ID: <20200218144037.GC14946@hirez.programming.kicks-ass.net>
Date:   Tue, 18 Feb 2020 15:40:37 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Carter Li 李通洲 <carter.li@...tek.com>,
        Pavel Begunkov <asml.silence@...il.com>,
        io-uring <io-uring@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org, Will Deacon <will@...nel.org>
Subject: Re: [PATCH] asm-generic/atomic: Add try_cmpxchg() fallbacks

On Tue, Feb 18, 2020 at 03:27:00PM +0100, Peter Zijlstra wrote:
> diff --git a/scripts/atomic/gen-atomic-fallback.sh b/scripts/atomic/gen-atomic-fallback.sh
> index b6c6f5d306a7..3c9be8d550e0 100755
> --- a/scripts/atomic/gen-atomic-fallback.sh
> +++ b/scripts/atomic/gen-atomic-fallback.sh
> @@ -140,6 +140,32 @@ cat <<EOF
>  EOF
>  }
>  
> +gen_try_cmpxchg_fallback()
> +{
> +	local order="$1"; shift;
> +
> +cat <<EOF
> +#ifndef try_cmpxchg${order}
> +#define try_cmpxchg${order}(_ptr, _oldp, _new) \\
> +({ \\
> +	typeof(*ptr) ___r, ___o = *(_oldp); \\
               *(_ptr)
> +	___r = cmpxchg${order}((_ptr), ___o, (_new)); \\
> +	if (unlikely(___r != ___o)) \\
> +		*(_old) = ___r; \\
		*(_oldp)
> +	likely(___r == ___o); \\
> +})
> +#endif /* try_cmpxchg${order} */

And it actually builds, as tested on an ARM build.