linux-kernel - Re: [PATCH v3 11/13] kmemleak: disable kasan instrumentation for kmemleak

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Message-ID: <20141001103930.GG20364@e104818-lin.cambridge.arm.com>
Date:	Wed, 1 Oct 2014 11:39:30 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Andrey Ryabinin <a.ryabinin@...sung.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Konstantin Serebryany <kcc@...gle.com>,
	Dmitry Chernenkov <dmitryc@...gle.com>,
	Andrey Konovalov <adech.fo@...il.com>,
	Yuri Gribov <tetra2005@...il.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Christoph Lameter <cl@...ux.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave.hansen@...el.com>,
	Andi Kleen <andi@...stfloor.org>,
	Vegard Nossum <vegard.nossum@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, Dave Jones <davej@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH v3 11/13] kmemleak: disable kasan instrumentation for
 kmemleak

On Mon, Sep 29, 2014 at 03:10:01PM +0100, Dmitry Vyukov wrote:
> On Fri, Sep 26, 2014 at 9:36 PM, Andrey Ryabinin <ryabinin.a.a@...il.com> wrote:
> > 2014-09-26 21:10 GMT+04:00 Dmitry Vyukov <dvyukov@...gle.com>:
> >> Looks good to me.
> >>
> >> We can disable kasan instrumentation of this file as well.
> >
> > Yes, but why? I don't think we need that.
> 
> Just gut feeling. Such tools usually don't play well together. For
> example, due to asan quarantine lots of leaks will be missed (if we
> pretend that tools work together, end users will use them together and
> miss bugs). I won't be surprised if leak detector touches freed
> objects under some circumstances as well.
> We can do this if/when discover actual compatibility issues, of course.

I think it's worth testing them together first.

One issue, as mentioned in the patch log, is that the size information
that kmemleak gets is the one from the kmem_cache object rather than the
original allocation size, so this would be rounded up.

Kmemleak should not touch freed objects (if an object is freed during a
scan, it is protected by some lock until the scan completes). There is a
bug however which I haven't got to fixing it yet, if kmemleak fails for
some reason (cannot allocate memory) and disables itself, it may access
some freed object (though usually hard to trigger).

-- 
Catalin
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