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

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Message-ID: <Pine.LNX.4.64.0706011721390.10254@schroedinger.engr.sgi.com>
Date:	Fri, 1 Jun 2007 17:26:00 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Srinivasa Ds <srinivasa@...ibm.com>,
	linux-kernel@...r.kernel.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, Andrew Morton wrote:

> I think it'd be better if we kept the WARN_ON_ONCE(size == 0) in there,

The trouble with the WARN_ON is that it triggers even for code that is 
okay like noted by Jeremy. My initial intend with NULL was to allow the 
allocation of a zero sized pointer without extra checks. It should only
trigger a failure if something bad was done.

NULL had the problem of confusion with no memory available. I think BADPTR 
is good. If the coding warts are causing trouble then BADPTR will result 
in a failure. Otherwise if the code is doing a kmalloc(0) and not 
dereferencing the pointer (like Paul's fixed code) then we should be fine 
and not issue a warning.

The false positives may be upsetting some people.
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