linux-kernel - Re: [PATCH] slub: Proper kmemleak tracking if CONFIG_SLUB

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Date:	Wed, 2 Oct 2013 17:25:28 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	"Bird, Tim" <Tim.Bird@...ymobile.com>,
	Frank Rowand <frowand.list@...il.com>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	"Bobniev, Roman" <Roman.Bobniev@...ymobile.com>,
	Andersson, Björn 
	<Bjorn.Andersson@...ymobile.com>
Subject: Re: [PATCH] slub: Proper kmemleak tracking if CONFIG_SLUB_DEBUG
 disabled

On Wed, Oct 02, 2013 at 04:57:12PM +0100, Christoph Lameter wrote:
> On Wed, 2 Oct 2013, Bird, Tim wrote:
> 
> > The problem child is actually the unconditional call to kmemleak_alloc()
> > in kmalloc_large_node() (in slub.c).  The problem comes because that call
> > is unconditional on CONFIG_SLUB_DEBUG but the kmemleak
> > calls in the hook routines are conditional on CONFIG_SLUB_DEBUG.
> > So if you have CONFIG_SLUB_DEBUG=n but CONFIG_DEBUG_KMEMLEAK=y,
> > you get the false reports.
> 
> Right. You need to put the #ifdef CONFIG_SLUB_DEBUG around the hooks that
> need it in the function itself instead of disabling the whole function if
> CONFIG_SLUB_DEUBG is not set.

If we are to do this, we also need a DEBUG_KMEMLEAK dependency,
something like:

	depends on (SLUB && SLUB_DEBUG) || !SLUB

or

	select SLUB_DEBUG if SLUB

Otherwise you get a lot of false positives.

But with any of the above, #ifdef'ing out kmemleak_* calls wouldn't make
much difference since they would already be no-ops in kmemleak.h with
!SLUB_DEBUG.

> > Personally, I like the idea of keeping bookeeping/tracing/debug stuff in hook
> > routines.  I also like de-coupling CONFIG_SLUB_DEBUG and CONFIG_DEBUG_KMEMLEAK,
> > but maybe others have a different opinon.  Unless someone speaks up, we'll
> > move the the currently in-function kmemleak calls into hooks, and all of the
> > kmemleak stuff out from under CONFIG_SLUB_DEBUG.
> > We'll have to see if the ifdefs get a little messy.
> 
> Decouple of you want. CONFIG_SLUB_DEBUG may duplicate what you already do.

I would prefer the decoupling but I'm fine either way (as long as the
dependencies are in place).

-- 
Catalin
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