linux-kernel - Re: [GIT PULL] SLAB changes for v2.6.39-rc1

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Date:	Thu, 24 Mar 2011 21:08:10 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Pekka Enberg <penberg@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	tj@...nel.org, npiggin@...nel.dk, rientjes@...gle.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [GIT PULL] SLAB changes for v2.6.39-rc1

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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