linux-kernel - Re: [BISECTED]: Kernel panic (was: Linux 5.7-rc2)

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Message-ID: <CAHk-=wiX+NT2yxtdPszH9U_S96MCNQA56GJFXY45mZc47yG5KQ@mail.gmail.com>
Date:   Tue, 21 Apr 2020 12:03:10 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Harald Arnesen <harald@...gtun.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Giovanni Gherdovich <ggherdovich@...e.cz>
Subject: Re: [BISECTED]: Kernel panic (was: Linux 5.7-rc2)

On Mon, Apr 20, 2020 at 1:52 AM Harald Arnesen <harald@...gtun.org> wrote:
>
> Neither rc1 nor rc2 will boot on my laptop. The attached picture is all
> I have been able to capture.

I know you saw the reply about this probably being fixed by

  https://lore.kernel.org/lkml/20200416054745.740-1-ggherdovich@suse.cz/

but it would be lovely if you could actually verify that that series
of four patches does indeed fix it for you.

Your oops is on that divide instruction:

        freq_scale = div64_u64(acnt, mcnt);

and while we had a check for mcnt not being zero earlier, we did

        mcnt *= arch_max_freq_ratio;

after that check. I could see it becoming zero either due to an
overflow, or due to arch_max_freq_ratio being 0.

I think the first commit in that series is supposed to fix that
arch_max_freq_ratio being 0 case, but it still feels like the code
that does the divide is checking for zero in the wrong place...

                  Linus