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Date: Mon, 19 Mar 2007 14:10:38 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Matt Mackall <mpm@selenic.com>
Cc: Christoph Lameter <clameter@sgi.com>,
       Pekka J Enberg <penberg@cs.helsinki.fi>, ast@domdv.de,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH] slab: deal with NULL pointers passed to kmem_cache_free
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On Mon, 19 Mar 2007 15:49:46 -0500
Matt Mackall <mpm@selenic.com> wrote:

> On Mon, Mar 19, 2007 at 10:08:03AM -0700, Christoph Lameter wrote:
> > On Mon, 19 Mar 2007, Pekka J Enberg wrote:
> > 
> > > This changes kmem_cache_free() to deal with NULL objects passed to it. The 
> > > current behavior is inconsistent with kfree() so there are callers 
> > > passing NULL to kmem_cache_free().
> > 
> > Hmmm.. kmem_cache_free is significantly different. One also needs to 
> > specify the slab cache.
> 
> I think this sort of thing should work:
> 
> a = kmalloc(...)
> b = kmem_cache_alloc(..)
> c = allocate_some_id(...)
> if (!a || !b || !c) {
>    free_some_id(c)
>    kmem_cache_free(c)
>    kfree(a);
>    return -ENOMEM;
> }

Would prefer to do:

static inline void kmem_cache_free_if_not_null(struct kmem_cache *cachep,
						void *objp)
{
	if (objp)
		kmem_cache_free(cachep, objp);
}

so that we don't add extra overhead to all the thousands of existing,
well-behaved callsites.