linux-kernel - Re: kmemcheck caught read from freed memory (cfq_free_io

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Date:	Wed, 2 Apr 2008 10:36:53 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Pekka Enberg <penberg@...helsinki.fi>
cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Jens Axboe <jens.axboe@...cle.com>, paulmck@...ux.vnet.ibm.com,
	Ingo Molnar <mingo@...e.hu>,
	Vegard Nossum <vegard.nossum@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: kmemcheck caught read from freed memory (cfq_free_io_context)

On Wed, 2 Apr 2008, Pekka Enberg wrote:

> On Wed, Apr 2, 2008 at 2:08 PM, Peter Zijlstra <a.p.zijlstra@...llo.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.
 
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