Date: Tue, 18 Nov 2014 22:15:31 +0100
From: Andi Kleen <andi@firstfloor.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrey Ryabinin <a.ryabinin@samsung.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Konstantin Serebryany <kcc@google.com>,
        Dmitry Chernenkov <dmitryc@google.com>,
        Andrey Konovalov <adech.fo@gmail.com>,
        Yuri Gribov <tetra2005@gmail.com>,
        Konstantin Khlebnikov <koct9i@gmail.com>,
        Sasha Levin <sasha.levin@oracle.com>, Michal Marek <mmarek@suse.cz>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        Christoph Lameter <cl@linux.com>, Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Dave Hansen <dave.hansen@intel.com>, Andi Kleen <andi@firstfloor.org>,
        Vegard Nossum <vegard.nossum@gmail.com>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org, linux-mm@kvack.org,
        Randy Dunlap <rdunlap@infradead.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Dave Jones <davej@redhat.com>, Jonathan Corbet <corbet@lwn.net>,
        Joe Perches <joe@perches.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6 00/11] Kernel address sanitizer - runtime memory
 debugger.
Message-ID: <20141118211531.GH12538@two.firstfloor.org>
References: <1404905415-9046-1-git-send-email-a.ryabinin@samsung.com>
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 <5461B906.1040803@samsung.com>
 <20141118125843.434c216540def495d50f3a45@linux-foundation.org>
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> It's a huge pile of tricky code we'll need to maintain.  To justify its
> inclusion I think we need to be confident that kasan will find a
> significant number of significant bugs that
> kmemcheck/debug_pagealloc/slub_debug failed to detect.

I would put it differently. kmemcheck is effectively too slow to run
regularly. kasan is much faster and covers most of kmemcheck.

So I would rather see it as a more practical replacement to
kmemcheck, not an addition.

> How do we get that confidence?  I've seen a small number of
> minorish-looking kasan-detected bug reports go past, maybe six or so. 
> That's in a 20-year-old code base, so one new minor bug discovered per
> three years?  Not worth it!
> 
> Presumably more bugs will be exposed as more people use kasan on
> different kernel configs, but will their number and seriousness justify
> the maintenance effort?

I would expect so. It's also about saving developer time.

IMHO getting better tools like this is the only way to keep
up with growing complexity.

> If kasan will permit us to remove kmemcheck/debug_pagealloc/slub_debug
> then that tips the balance a little.  What's the feasibility of that?

Maybe removing kmemcheck. slub_debug/debug_pagealloc are simple, and are in
different niches (lower overhead debugging)

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only.
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