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Date: Sat, 26 Mar 2011 20:57:22 +0100
From: Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH] slub: Disable the lockless allocator
Message-ID: <20110326195722.GA7748@elte.hu>
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To: Christoph Lameter <cl@linux.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>, Pekka Enberg <penberg@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, 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


* Christoph Lameter <cl@linux.com> wrote:

> On Sat, 26 Mar 2011, Christoph Lameter wrote:
> 
> > Tejun: Whats going on there? I should be getting offsets into the per cpu
> > area and not kernel addresses.
> 
> Its a UP kernel running on dual Athlon. So its okay ... Argh.... The
> following patch fixes it by using the fallback code for cmpxchg_double:
> 
> 
> 
> Subject: per_cpu: Fixup cmpxchg_double for !SMP
> 
> cmpxchg_double should only be provided for SMP. In the UP case
> the GS register is not defined and the function will fail.
> 
> Signed-off-by: Christoph Lameter <cl@linux.com>

I.e. the bug got introduced by:

 | commit b9ec40af0e18fb7d02106be148036c2ea490fdf9
 | Author: Christoph Lameter <cl@linux.com>
 | Date:   Mon Feb 28 11:02:24 2011 +0100
 |
 |     percpu, x86: Add arch-specific this_cpu_cmpxchg_double() support

and then the lockless allocator made use of it, right?

Thanks,

	Ingo

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