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

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Date:	Wed, 2 Apr 2008 14:11:42 +0300
From:	"Pekka Enberg" <penberg@...helsinki.fi>
To:	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>
Cc:	"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>,
	"Christoph Lameter" <clameter@....com>
Subject: Re: kmemcheck caught read from freed memory (cfq_free_io_context)

On Wed, 2008-04-02 at 13:07 +0200, Jens Axboe wrote:
> > Makes sense, and to me Pauls analysis of the code looks totally correct
> > - there's no bug there, at least related to hlist traversal and
> > kmem_cache_free(), since we are under rcu_read_lock() and thus hold off
> > the grace for freeing.

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.
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