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

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Date:   Wed, 22 Apr 2020 11:32:53 +0200
From:   Harald Arnesen <harald@...gtun.org>
To:     Linus Torvalds <torvalds@...ux-foundation.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)

Linus Torvalds [21.04.2020 21:03]:

> 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

I will try the patches today, and report back.
-- 
Hilsen Harald