linux-kernel - Re: [PATCH] modules fix incorrect percpu usage

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Date:	Wed, 31 Mar 2010 11:15:49 +0900
From:	Tejun Heo <tj@...nel.org>
To:	rostedt@...dmis.org
CC:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Eric Dumazet <dada1@...mosbay.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...e.de>, stable <stable@...nel.org>
Subject: Re: [PATCH] modules fix incorrect percpu usage

On 03/31/2010 11:03 AM, Steven Rostedt wrote:
> I don't know. A possible "NULL pointer dereference" seems to me to be a
> pretty big user visible impact.
> 
> I guess the question is, what's the risk of adding this change?

AFAICS, the risk is fairly low.  per_cpu_ptr(pcpudest, cpu) is
SHIFT_PERCPU_PTR((ptr), per_cpu_offset((cpu))) which is just a fancy
way of saying "typeof(ptr)((unsigned long)(ptr) + per_cpu_offset(cpu))"
with enough obfuscation to prevent gcc from optimizing it incorrectly.

Thanks.

-- 
tejun
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