linux-kernel - Re: SLUB: Return ZERO_SIZE

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Message-ID: <Pine.LNX.4.64.0706041532350.27125@schroedinger.engr.sgi.com>
Date:	Mon, 4 Jun 2007 15:39:08 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Pekka Enberg <penberg@...helsinki.fi>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: SLUB: Return ZERO_SIZE_PTR for kmalloc(0)

On Mon, 4 Jun 2007, Pekka Enberg wrote:

> Christoph Lameter wrote:
> > That is another patchset. See
> > http://marc.info/?l=linux-kernel&w=2&r=1&s=DEVELKERNEL&q=b
> 
> Oh my, I am totally confused now.
> 
> First you fix kmalloc(0) to be legal and safe. And then you want to
> DEVEL_WARN_ON_ONCE when size is zero so people can fix their code?
> 
> I don't get it.

Sorry complex situation. Andrew wants the warnings, Linus wants the 
ZERO_SIZE_PTR. Not sure where we are going here.

> I thought we wanted to support kmalloc(0) so that as long as you don't
> dereference the pointer, it's all legal and good. Right? So we obviously
> should shut up the WARN_ON because if you do oops, you can clearly see that it
> happened at ZERO_SIZE_PTR and have a nice stack trace anyway...

Well so far we agreed to keep the warnings in at least till release data 
and I have not heard differently yet.

> Btw, if I am again missing something totally obvious, could you please be so
> kind to send me a batch of the same pills that the smart people take. I am all
> out.

Heheheh.... Mind boogling isnt it? Patch duplicity....

Seriously: Andrew/Linus could you make up your mind which way we are 
going here? 

I'd say lets drop the DEVELKERNEL stuff and the warnings and go with 
ZERO_SIZE_PTR. The DEVELKERNEL patch has the danger that subtle changes 
occur at release time that we have not anticipated.

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