From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Lameter <cl@linux.com>
Subject: Re: FIX [1/2] slub: Do not dereference NULL pointer in node_match
Date: Thu, 24 Jan 2013 15:14:43 +0000
Message-ID: <0000013c6d200e1d-03ae09c1-6fb8-42eb-ab6c-8fcae05fdb6e-000000@email.amazonses.com>
References: <20130123214514.370647954@linux.com> <0000013c695fbd30-9023bc55-f780-4d44-965f-ab4507e483d5-000000@email.amazonses.com> <1358988824.3351.5.camel@kernel>
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Cc: Pekka Enberg <penberg@kernel.org>, Steven Rostedt <rostedt@goodmis.org>,
    Thomas Gleixner <tglx@linutronix.de>, RT <linux-rt-users@vger.kernel.org>,
    Clark Williams <clark@redhat.com>, John Kacur <jkacur@gmail.com>,
    "Luis Claudio R. Goncalves" <lgoncalv@redhat.com>,
    Joonsoo Kim <js1304@gmail.com>, Glauber Costa <glommer@parallels.com>,
    linux-mm@kvack.org, David Rientjes <rientjes@google.com>,
    elezegarcia@gmail.com
To: Simon Jeons <simon.jeons@gmail.com>
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In-Reply-To: <1358988824.3351.5.camel@kernel>
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On Wed, 23 Jan 2013, Simon Jeons wrote:

> On Wed, 2013-01-23 at 21:45 +0000, Christoph Lameter wrote:
> > The variables accessed in slab_alloc are volatile and therefore
> > the page pointer passed to node_match can be NULL. The processing
> > of data in slab_alloc is tentative until either the cmpxhchg
> > succeeds or the __slab_alloc slowpath is invoked. Both are
> > able to perform the same allocation from the freelist.
> >
> > Check for the NULL pointer in node_match.
> >
> > A false positive will lead to a retry of the loop in __slab_alloc.
>
> Hi Christoph,
>
> Since page_to_nid(NULL) will trigger bug, then how can run into
> __slab_alloc?

page = NULL

	 ->

node_match(NULL, xx) = 0

 	->

call into __slab_alloc.

__slab_alloc() will check for !c->page which requires the assignment of a
new per cpu slab page.

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