Bug#971406: gnome-shell: freezes when laptop is configured for external display only

[Simon McVittie]

Control: reassign -1 gnome-shell 3.30.2-11~deb10u2
Control: retitle -1 gnome-shell: freezes when laptop is configured for external display only
Control: tags -1 + moreinfo buster

On Tue, 29 Sep 2020 at 18:58:55 -0400, tom wrote:
> Gnome-conrol-center > devices > displays > external monitor set
> to primary in 'join displays'> 'single display'
> turns off both LVDS and external monitor, freezes keyboard and 
> mouse control

gnome-control-center only changes configuration and doesn't actually
implement the display change, so I'm reassigning this to gnome-shell,
which is the component that -control-center is configuring. Please
send the output of "reportbug --template gnome-shell" so that we can
see the versions of all the related packages. For now I'm assuming that
it's the latest version from Debian 10.6.

If you repeat the configuration that caused the freeze, does it happen
reliably?

What messages appear in the system log (/var/log/syslog or the systemd
journal) when this happens?

Are you using the Wayland or Xorg version of the GNOME session?

What hardware are you using? You mentioned LVDS, so presumably it's a
laptop. What graphics device does it have? lspci, from the pciutils
package, should list a "VGA compatible controller", perhaps more than
one.

Are you using any GNOME Shell extensions? If you are, please try disabling
them all and see whether the bug persists.

> hard reboot only solution

Here are some things that might make a hard reboot unnecessary:

* press Ctrl+Alt+Delete repeatedly (more than 7 times in 2 seconds)
  to reboot semi-gracefully

* press Ctrl+Alt+F6, then Ctrl+Alt+Delete repeatedly

* use "magic sysrq key" sequences
  (https://en.wikipedia.org/wiki/Magic_SysRq_key#Uses)
  to reboot less gracefully

Do any of those work? If they do, that gives us useful information about
which layers of the system have stopped working and which layers still work.

> If 'mirror' is used, the external monitor is available, but only at
> the resolution of the LVDS or lower. 

Mirroring can only happen at resolutions that are supported by both
displays, so that part isn't a bug.

    smcv