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

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Message-Id: <1207133344.8514.759.camel@twins>
Date:	Wed, 02 Apr 2008 12:49:04 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	paulmck@...ux.vnet.ibm.com, Jens Axboe <jens.axboe@...cle.com>,
	Vegard Nossum <vegard.nossum@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Christoph Lameter <clameter@....com>
Subject: Re: kmemcheck caught read from freed memory (cfq_free_io_context)

On Wed, 2008-04-02 at 13:46 +0300, Pekka Enberg wrote:
> Hi Paul,
> 
> On Wed, Apr 2, 2008 at 1:40 PM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
> >  I am still confused.
> >
> >  o       The kmem_cache has SLAB_DESTROY_BY_RCU.
> >
> >  o       This means that a given slab should not be returned to the
> >         system until a grace period elapses.
> 
> Yeah, that's what I thought too, that this is a SLUB bug but Peter
> convinced me otherwise. SLUB keeps the _page_ around so the pointer
> will be _valid_, although it might not be _your_ pointer so the caller
> needs to do some validation step. Or at least that's how I understood
> what Peter was saying.

Correct, that is always how i understood SLAB_DESTROY_BY_RCU to work.

Does SLAB (as opposed to SLUB) do it differently?

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