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Date:	Tue, 10 May 2011 13:03:41 +0300
From:	Pekka Enberg <>
To:	Eric Dumazet <>
CC:	Christoph Lameter <>,
	Pekka Enberg <>,,
	Andrew Morton <>,,,,
	Vegard Nossum <>
Subject: Re: [Bugme-new] [Bug 33502] New: Caught 64-bit read from uninitialized
 memory in __alloc_skb

On 5/10/11 11:43 AM, Eric Dumazet wrote:
> Le lundi 09 mai 2011 à 15:04 -0500, Christoph Lameter a écrit :
>> On Mon, 9 May 2011, Pekka Enberg wrote:
>>> On Wed, 20 Apr 2011, Eric Dumazet wrote:
>>>> [PATCH v4] slub: dont use cmpxchg_double if KMEMCHECK or DEBUG_PAGEALLOC
>>>> Christian Casteyde reported a KMEMCHECK splat in slub code.
>>>> Problem is now we are lockless and allow IRQ in slab_alloc(), the object
>>>> we manipulate from freelist can be allocated and freed right before we
>>>> try to read object->next.
>>>> Same problem can happen with DEBUG_PAGEALLOC
>>>> Just dont use cmpxchg_double() if either CONFIG_KMEMCHECK or
>>> Christoph, Eric, is this still relevant after commit 1759415 ("slub: Remove
>>> CONFIG_CMPXCHG_LOCAL ifdeffery") in slab/next of slab.git?
>> There is still an issue and now you can no longer fix the thing through
>> It needs to be legal for slub to deref the counter even if the object has
>> been freed.
> I am trying to follow things but honestly I am lost.
> Isnt commit 1759415e63 planned for 2.6.40 ?
> ( ref :
>;a=commitdiff;h=1759415e630e5db0dd2390df9f94892cbfb9a8a2 )
> How shall we fix things for 2.6.39 ? I thought my patch was OK for that.
> Its a bit hard to work with you on this stuff, for a report I made ages
> ago, I find it incredible its not yet fixed in linux-2.6.
Can't we fix the issue by putting kmemcheck_mark_initialized() to 
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