linux-kernel - Re: [RFC] [PATCH] cpuset operations causes Badness at mm/slab.c:777 warning

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Message-Id: <20070601135900.ec44b1aa.akpm@linux-foundation.org>
Date:	Fri, 1 Jun 2007 13:59:00 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Lameter <clameter@....com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Srinivasa Ds <srinivasa@...ibm.com>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Dinakar Guniguntala <dino@...ibm.com>, pj@....com,
	simon.derr@...l.net, clameter@...ulhu.engr.sgi.com,
	rientjes@...gle.com
Subject: Re: [RFC] [PATCH] cpuset operations causes Badness at mm/slab.c:777
 warning

On Fri, 1 Jun 2007 13:47:23 -0700 (PDT)
Christoph Lameter <clameter@....com> wrote:

> On Fri, 1 Jun 2007, Jeremy Fitzhardinge wrote:
> 
> > I think this is a good example of why having to special-case kmalloc(0)
> > is a bad idea.  The original code was straightforward and, barring
> > silliness, should be completely correct with npids==0.  This new code
> > does nothing other than make things more complex.
> 
> Hehe we got you. The code is indexing the pidarray allocated with 
> kmalloc(0). So it uncovered a latent bug. It only worked because SLAB gave 
> him 32 bytes and it now only works because SLUB give him 8. That is enough 
> to illegally index the first array element.
> 

Poisoning and redzoning could have caught that.

But I guess it doesn't matter now, as this shortcoming is specific to
the zero-length allocations, and we're weeding those out anyway.
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