linux-kernel - Re: [RFC PATCH] x86: Use volatile semantics for atomic

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Message-ID: <CAJhHMCC7RKE9GE3fGx0pnNoZHL0r_MOPMPwCjjNNbnC6i0G=BA@mail.gmail.com>
Date:	Mon, 22 Sep 2014 17:42:16 -0400
From:	Pranith Kumar <bobby.prani@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"maintainer:X86 ARCHITECTURE..." <x86@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"open list:X86 ARCHITECTURE..." <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] x86: Use volatile semantics for atomic_set()

On Mon, Sep 22, 2014 at 4:08 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, Sep 22, 2014 at 03:39:21PM -0400, Pranith Kumar wrote:
>> All the atomic operations have volatile semantics to prevent compiler
>> reordering. Enforce the same semantics for atomic_set() too.
>
> To what point? atomic_set() is typically not what you expect it to
> anyhow.

This is the only atomic operation which allows compiler reordering. I
am not sure why this exception was made. Any ideas as to why we do
this?

As I mentioned, this patch removes this inconsistency by disallowing
compiler reordering.

-- 
Pranith
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