Subject: bug#76554: Laptop screen blank after kexec reboot

From: Ludovic Courtès <[email-masked]>
Date: Tue, 04 Mar 2025 15:36:00 +0100

Hi Simon,

(Cc: kernel team.)

Simon Streit <[email-masked]> skribis:

> I just did a reboot with kexec from kexec-tools on an identical machine
> running Debian Bookworm with LUKS encryption:
>
> The screen goes on with a blinking prompt.  The external video is on too
> and can plug it in and out again.
>
> I just tried it manually with kexec from kexec-tools in Guix.  The
> display stayed dark here too and I somehow didn't manage to unlock
> the device.  The HDD-Lamp hinted that something was happening.
>
> I looked into dmesg and /var/log/messages.  I see a time gap until the
> partition is mounted.  But no hint that a video or state of hardware is
> being changed:

Interesting.  Could it be that we’re missing something from the kernel?
The syscall interface that we use in Guix (kexec_file_load(2)) and
Shepherd (reboot(2)) is very high-level and we cannot get more control
on graphics or whatever at that level.

I just checked and systemd invokes the ‘kexec’ program from kexec-tools.
I don’t think the ‘kexec’ program is doing anything more in the
‘kexec_file_load’ case (it can also use the obsolescent kexec_load(2)
and in fact most of the code is here to handle that case).

Thoughts?

Ludo’.