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Date: Wed, 2 Apr 2008 10:36:53 -0700 (PDT)
From: Christoph Lameter <clameter@sgi.com>
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To: Pekka Enberg <penberg@cs.helsinki.fi>
cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
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       Ingo Molnar <mingo@elte.hu>, Vegard Nossum <vegard.nossum@gmail.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: kmemcheck caught read from freed memory (cfq_free_io_context)
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On Wed, 2 Apr 2008, Pekka Enberg wrote:

> On Wed, Apr 2, 2008 at 2:08 PM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> >  but what holds off the slab allocator re-issueing that same object and
> >  someone else writing other stuff into it?
> 
> Nothing. So you cannot access the object at all after you've called
> kmem_cache_free(). SLAB_RCU or no SLAB_RCU.

You can of course access the object. And if you establish a definite state 
of locks on free (and through a ctor) then its even okay to take locks.