linux-kernel - Re: [PATCH 2.6.28-rc5 03/11] kmemleak: Add the memory allocation/freeing hooks

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Message-Id: <1227265627.7015.7.camel@pc1117.cambridge.arm.com>
Date:	Fri, 21 Nov 2008 11:07:07 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	linux-kernel@...r.kernel.org, Matt Mackall <mpm@...enic.com>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH 2.6.28-rc5 03/11] kmemleak: Add the memory
	allocation/freeing hooks

Hi Pekka,

On Thu, 2008-11-20 at 21:30 +0200, Pekka Enberg wrote:
> > @@ -2610,6 +2611,9 @@ static struct slab *alloc_slabmgmt(struct kmem_cache *cachep, void *objp,
> >                /* Slab management obj is off-slab. */
> >                slabp = kmem_cache_alloc_node(cachep->slabp_cache,
> >                                              local_flags & ~GFP_THISNODE, nodeid);
> > +               /* only scan the list member to avoid false negatives */
> > +               memleak_scan_area(slabp, offsetof(struct slab, list),
> > +                                 sizeof(struct list_head));
> 
> I find this comment somewhat confusing. Does it mean we _must_ scan
> the list members to avoid false negatives (i.e. leaks that happened
> but were not reported) or that if we scan the whole of struct slab, we
> get false negatives?

It's been some time since I first added this and I may not remember the
full details but it's the latter case - it should avoid scanning
slabp->s_mem because (my understanding) is that it may contain a pointer
to an allocated block. Kmemleak only allows adding what sections to
scan, so in this case only the list_head is relevant.

Let me know if my understanding is correct and I'll make the comment
more clear.

Thanks.

-- 
Catalin

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