linux-kernel - Re: Linux 2.6.25-rc2

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Date:	Wed, 27 Feb 2008 17:57:26 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Lameter <clameter@....com>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Torsten Kaiser <just.for.lkml@...glemail.com>,
	Ingo Molnar <mingo@...e.hu>,
	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

On Wed, 27 Feb 2008 15:32:52 -0800 (PST) Christoph Lameter <clameter@....com> wrote:

> On Tue, 19 Feb 2008, Mathieu Desnoyers 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.  But on some other
architectures ++ on u32 is not atomic wrt interrutps, so they should use
atomic_t or some other arch-specific mechanism.

And guess what?  It's already all been done: local_t.
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