linux-kernel - Re: [PATCH] net: fix race in the receive/select

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Message-ID: <20090701062732.GK6760@one.firstfloor.org>
Date:	Wed, 1 Jul 2009 08:27:32 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Andi Kleen <andi@...stfloor.org>, jolsa@...hat.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	fbl@...hat.com, nhorman@...hat.com, davem@...hat.com,
	oleg@...hat.com, eric.dumazet@...il.com
Subject: Re: [PATCH] net: fix race in the receive/select

On Wed, Jul 01, 2009 at 11:39:24AM +0800, Herbert Xu wrote:
> Andi Kleen <andi@...stfloor.org> wrote:
> > 
> > At least on x86 I can't see how it happens. mb() is only a compile
> > time barrier and the compiler doesn't optimize over indirect callbacks
> > like __pollwait() anyways.
> 
> mb() does more than just a compiler barrier, it also issues mfence.

mfence is not needed for normal C code (not using non temporal
stores) in the Linux memory model on x86 and is a no-op. Only the compile
time barrier matters.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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