linux-kernel - Re: [BISECTED] bug/regression, x86-64: completely unbootable machine

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Message-ID: <1587715859.28179.17.camel@suse.cz>
Date:   Fri, 24 Apr 2020 10:10:59 +0200
From:   Giovanni Gherdovich <ggherdovich@...e.cz>
To:     Rui Salvaterra <rsalvaterra@...il.com>, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [BISECTED] bug/regression, x86-64: completely unbootable machine

On Fri, 2020-04-24 at 09:00 +0100, Rui Salvaterra wrote:
> Hi, everyone,
> 
> Starting with Linux 5.7-rc1, my Arrandale (Core i3-380M) laptop is
> completely unbootable (the last messages on screen are GRUB's loading
> kernel/initramfs). I was hoping someone would have noticed it before
> 5.7-rc2 had been tagged, but alas. Anyway, I bisected it down to
> commit 1567c3e3467cddeb019a7b53ec632f834b6a9239 (x86, sched: Add
> support for frequency invariance). After reverting it, the machine
> boots again, obviously.
> 
> Let me know if you need any further info in order to fix this issue.
> 
> Complete bisection log follows.
> [...]

Hello Rui,

thanks for the report.

The problem you encountered is due to a bug where the code doesn't work on
machines with less than 4 physical CPU cores. It is fixed by this patch
series:

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

The series has been merged in the branch sched/urgent of the "tip" tree
(https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git), the commit
fixing the bug you observed is 23ccee22e834 (x86, sched: Account for CPUs
with less than 4 cores in freq. invariance), and will be merged in Linus'
tree at some point.

Thanks,
Giovanni Gherdovich