linux-kernel - Re: [PATCH] x86: cmpxchg_double: Add missing memory clobber

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Message-ID: <20151007130036.GB7520@twins.programming.kicks-ass.net>
Date:	Wed, 7 Oct 2015 15:00:36 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Pranith Kumar <bobby.prani@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
	"open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: cmpxchg_double: Add missing memory clobber

On Tue, Oct 06, 2015 at 02:39:02PM -0700, H. Peter Anvin wrote:

> However, I think one of the major uses for cmpxchg_double() is for page
> table manipulation, and for that it isn't clear that a compiler barrier
> is needed nor desired.

See mm/slub.c, that uses cmpxchg_double() (the LOCK prefixed one) and
one would expect that to also include a compiler barrier.
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