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Date: Wed, 31 Mar 2010 11:15:49 +0900
From: Tejun Heo <tj@kernel.org>
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CC: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
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       Randy Dunlap <randy.dunlap@oracle.com>,
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       Linus Torvalds <torvalds@linux-foundation.org>,
       Greg Kroah-Hartman <gregkh@suse.de>, stable <stable@kernel.org>
Subject: Re: [PATCH] modules fix incorrect percpu usage
References: <20100330135208.GC20673@Krystal>	 <20100330125304.53f079db.akpm@linux-foundation.org>	 <20100330202421.GA28800@Krystal> <1270001013.19685.6677.camel@gandalf.stny.rr.com>
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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