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Subject: Re: [BISECTED]: Kernel panic (was: Linux 5.7-rc2)
To:     Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Giovanni Gherdovich <ggherdovich@suse.cz>
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 <428bac87-b6dd-0867-c8f8-622cd606de3e@skogtun.org>
 <CAHk-=wiX+NT2yxtdPszH9U_S96MCNQA56GJFXY45mZc47yG5KQ@mail.gmail.com>
From:   Harald Arnesen <harald@skogtun.org>
Message-ID: <395f63b5-a24b-0eb9-4cb2-06057c1882d8@skogtun.org>
Date:   Wed, 22 Apr 2020 11:32:53 +0200
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Linus Torvalds [21.04.2020 21:03]:

> On Mon, Apr 20, 2020 at 1:52 AM Harald Arnesen <harald@skogtun.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