linux-kernel - Re: Linux 2.6.25-rc2

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Date:	Thu, 28 Feb 2008 09:14:12 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Christoph Lameter <clameter@....com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Torsten Kaiser <just.for.lkml@...glemail.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Eric Dumazet <dada1@...mosbay.com>
Subject: Re: Linux 2.6.25-rc2


* Andrew Morton <akpm@...ux-foundation.org> wrote:

> > > incrementing the variable with a "++" when interrupts are not 
> > > disabled. It's not an atomic add and it's racy. The code within 
> > > stat() does exactly this.
> > 
> > Yes but that is only for used for statistics which can be racy. Note 
> > that the VM event statistics also can be racy.
> 
> Doing ++ on a u32 _is_ atomic wrt interrupts on x86 and probably lots 
> of other architectures, so we're OK using unsigned there. [...]

hm, why should it be atomic wrt. irqs? There's nothing that keeps gcc 
from not doing an "incl memory_address" but do something like: "load 
memory address into regx, incl regx, ... store address into memory 
address" - and that's not atomic at that point.

	Ingo
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