linux-kernel - Re: [PATCH 1/2] mm/kasan: avoid duplicate KASAN issues from reporting

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Message-ID: <CANpmjNOT7xVbv4P1n3X24-HH8VMBs7Ny33DFYbzjO6Gqza2mZA@mail.gmail.com>
Date:   Thu, 22 Apr 2021 16:10:37 +0200
From:   Marco Elver <elver@...gle.com>
To:     Maninder Singh <maninder1.s@...sung.com>
Cc:     Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, a.sahrawat@...sung.com,
        Vaneet Narang <v.narang@...sung.com>
Subject: Re: [PATCH 1/2] mm/kasan: avoid duplicate KASAN issues from reporting

On Thu, 22 Apr 2021 at 11:17, Maninder Singh <maninder1.s@...sung.com> wrote:
>
> when KASAN multishot is ON and some buggy code hits same code path
> of KASAN issue repetetively, it can flood logs on console.
>
> Check for allocaton, free and backtrace path at time of KASAN error,
> if these are same then it is duplicate error and avoid these prints
> from KASAN.

On a more fundamental level, I think this sort of filtering is the
wrong solution to your problem. One reason why it's good that
multishot is off by default is, because _every_ KASAN report is
critical and can destabilize the system. Therefore, any report after
the first one might be completely bogus, because the system is in a
potentially bad state and its behaviour might be completely random.

The correct solution is to not leave the system running, fix the first
bug found, continue; rinse and repeat. Therefore, this patch adds a
lot of code for little benefit.

The much simpler solution that will likely yield a similar result is
to simply define an upper bound on the number of reports if multishot
is on. Because if I've seen 1000 reports, I already know the system is
completely trashed and whatever else it's reporting might just be
random.

Thanks,
-- Marco