linux-kernel - Re: mm: slub: invalid memory access in setup

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Message-Id: <20140701144947.5ce3f93729759d8f38d7813a@linux-foundation.org>
Date:	Tue, 1 Jul 2014 14:49:47 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Lameter <cl@...two.org>
Cc:	David Rientjes <rientjes@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Wei Yang <weiyang@...ux.vnet.ibm.com>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: mm: slub: invalid memory access in setup_object

On Tue, 1 Jul 2014 09:58:52 -0500 (CDT) Christoph Lameter <cl@...two.org> wrote:

> On Mon, 30 Jun 2014, David Rientjes wrote:
> 
> > It's not at all clear to me that that patch is correct.  Wei?
> 
> Looks ok to me. But I do not like the convoluted code in new_slab() which
> Wei's patch does not make easier to read. Makes it difficult for the
> reader to see whats going on.
> 
> Lets drop the use of the variable named "last".
> 
> 
> Subject: slub: Only call setup_object once for each object
> 
> Modify the logic for object initialization to be less convoluted
> and initialize an object only once.
> 

Well, um.  Wei's changelog was much better:

: When a kmem_cache is created with ctor, each object in the kmem_cache will
: be initialized before use.  In the slub implementation, the first object
: will be initialized twice.
: 
: This patch avoids the duplication of initialization of the first object.
: 
: Fixes commit 7656c72b5a63: ("SLUB: add macros for scanning objects in a
: slab").

I can copy that text over and add the reported-by etc (ho hum) but I
have a tiny feeling that this patch hasn't been rigorously tested? 
Perhaps someone (Wei?) can do that?

And we still don't know why Sasha's kernel went oops.
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