linux-kernel - Re: [PATCH v4 1/8] atomics: add acquire/release/relaxed variants of some atomic operations

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Message-ID: <20150803172658.GX25159@twins.programming.kicks-ass.net>
Date:	Mon, 3 Aug 2015 19:26:58 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Will Deacon <will.deacon@....com>
Cc:	linux-arch@...r.kernel.org, Waiman.Long@...com,
	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	mingo@...nel.org
Subject: Re: [PATCH v4 1/8] atomics: add acquire/release/relaxed variants of
 some atomic operations

On Mon, Aug 03, 2015 at 06:02:24PM +0100, Will Deacon wrote:
> +/*
> + * The idea here is to build acquire/release variants by adding explicit
> + * barriers on top of the relaxed variant. In the case where the relaxed
> + * variant is already fully ordered, no additional barriers are needed.
> + */
> +#define __atomic_op_acquire(ret_t, op, ...)				\
> +({									\
> +	ret_t __ret = op##_relaxed(__VA_ARGS__);			\

Do you really need ret_t? Can't we use typeof() on the expression?

> +	smp_mb__after_atomic();						\
> +	__ret;								\
> +})

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