linux-kernel - Re: [PATCH] mm: kill kmemcheck again

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Message-ID: <20171002072904.cpfp6gkaakag7icm@dhcp22.suse.cz>
Date:   Mon, 2 Oct 2017 09:29:04 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>
Cc:     Vegard Nossum <vegard.nossum@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH] mm: kill kmemcheck again

On Sat 30-09-17 20:02:41, Sasha Levin wrote:
> On Sat, Sep 30, 2017 at 03:57:27PM +0200, Vegard Nossum wrote:
> >On 30 September 2017 at 11:48, Steven Rostedt <rostedt@...dmis.org> wrote:
> >> On Wed, 27 Sep 2017 17:02:07 +0200
> >> Michal Hocko <mhocko@...nel.org> wrote:
> >>
> >>> > Now that 2 years have passed, and all distros provide gcc that supports
> >>> > KASAN, kill kmemcheck again for the very same reasons.
> >>>
> >>> This is just too large to review manually. How have you generated the
> >>> patch?
> >>
> >> I agree. This needs to be taken out piece by piece, not in one go,
> >> where there could be unexpected fallout.
> >
> >I have a patch from earlier this year that starts by removing the core
> >code and defining all the helpers/flags as no-ops so they can be
> >removed bit by bit at a later time. See the attachment. Pekka signed
> >off on it too.
> >e
> >I never actually submitted this because I was waiting for MSAN to be
> 
> I'm not sure how much value there is in doing it this way. I agree
> that the patch is big, but most of it is simply removing code under
> arch/x86/mm/kmemcheck.
>
> The difference between Vegard's patch and mine is about 300 lines
> (out of 2800+), where those 300 lines are simply removing calls to
> kmemcheck. There are no logic changes. (so something very similar to
> 's/*kmemcheck*//g' would do the trick).

Maybe splitting the patch into three: 1) remove all callers of kmemleak
API and 2) remove arch/x86/mm/kmemcheck/ and 3) remove leftovers would
be slightly easier to review. Maybe 2 and 3 would have some dependencies
so they would have to end up in the same path.

Just my 2c

-- 
Michal Hocko
SUSE Labs