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Date: Fri, 1 Jun 2007 13:59:00 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Christoph Lameter <clameter@sgi.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>, Srinivasa Ds <srinivasa@in.ibm.com>,
       linux-kernel@vger.kernel.org,
       Linus Torvalds <torvalds@linux-foundation.org>,
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       clameter@cthulhu.engr.sgi.com, rientjes@google.com
Subject: Re: [RFC] [PATCH] cpuset operations causes Badness at mm/slab.c:777
 warning
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On Fri, 1 Jun 2007 13:47:23 -0700 (PDT)
Christoph Lameter <clameter@sgi.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.