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Subject: Re: [GIT PULL] SLAB changes for v2.6.39-rc1
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>, Ingo Molnar <mingo@elte.hu>,
        torvalds@linux-foundation.org, akpm@linux-foundation.org,
        tj@kernel.org, npiggin@kernel.dk, rientjes@google.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
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Content-Type: text/plain; charset="UTF-8"
Date: Thu, 24 Mar 2011 21:08:10 +0100
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Le jeudi 24 mars 2011 à 14:51 -0500, Christoph Lameter a écrit :
> On Thu, 24 Mar 2011, Pekka Enberg wrote:
> 
> > Thanks, Ingo! Christoph, may I have your sign-off for the patch and
> > I'll send it to Linus?
> 
> 
> Subject: SLUB: Write to per cpu data when allocating it
> 
> It turns out that the cmpxchg16b emulation has to access vmalloced
> percpu memory with interrupts disabled. If the memory has never
> been touched before then the fault necessary to establish the
> mapping will not to occur and the kernel will fail on boot.
> 
> Fix that by reusing the CONFIG_PREEMPT code that writes the
> cpu number into a field on every cpu. Writing to the per cpu
> area before causes the mapping to be established before we get
> to a cmpxchg16b emulation.
> 


Thats strange, alloc_percpu() is supposed to zero the memory already ...

Are you sure its really this problem of interrupts being disabled ?


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