linux-kernel - Re: [RFC 0/4] CONFIG_STABLE to switch off development checks

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Message-Id: <1180797790.18535.6.camel@kleikamp.austin.ibm.com>
Date:	Sat, 02 Jun 2007 10:23:10 -0500
From:	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Christoph Lameter <clameter@....com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, akpm@...ux-foundation.org
Subject: Re: [RFC 0/4] CONFIG_STABLE to switch off development checks

On Fri, 2007-06-01 at 11:58 -0700, Jeremy Fitzhardinge wrote:
> Christoph Lameter wrote:
> > Hmmm... We got there because SLUB initially return NULL for kmalloc(0). 
> > Rationale: The user did not request any memory so we wont give him 
> > any.
> >
> > That (to my surprise) caused some strange behavior of code and so we then 
> > decided to keep SLAB behavior and return the smallest available object 
> > size and put a warning in there. At some later point we plan to switch
> > to returning NULL for kmalloc(0).
> >   
> 
> Unfortunately, returning NULL is indistinguishable from ENOMEM, so the
> caller would have to check to see how much it asked for before deciding
> to really fail, which doesn't help things much.
> 
> Or does it (should it) return ERRPTR(-ENOMEM)?  Bit of a major API
> change if not.

I'm on Christoph's side here.  I don't think it makes sense for any code
to ask to allocate zero bytes of memory and expect valid memory to be
returned.

Would a compromise be to return a pointer to some known invalid region?
This way the kmalloc(0) call would appear successful to the caller, but
any access to the memory would result in an exception.

Just my 2 cents,
Shaggy
-- 
David Kleikamp
IBM Linux Technology Center

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