third-party applications freeze gnome-shell reproducibly

[Nicolas Herzog]

On my Ubuntu 20.04.3 LTS, I have reproducible freezes of gdm3 (3.36.3-0ubuntu0.20.04.4) caused by third-party applications. The only thing I found describing my problem was https://unix.stackexchange.com/a/39855 (passage *GUI Glitches Causing Unresponsive WM or X11/Wayland*). This is exactly my experience ("**an application stops responding and prevents you from entering input with the keyboard or mouse to other application windows**"). Specifically:
- clicking on a hyperlink in (an open mail in) thunderbird freezes gdm3 at 90%.
- opening files via nemo (file manager) freezes gdm3 sometimes, regardless which file type.
- libreoffice freezes gdm3 a lot when switching windows via alt-tab, but not when I switch windows via super key.

Whenever a freeze occurs, the clock in my taskbar stops, the mouse and keyboard still work, but no window responds. Switching to tty works. Killing the last used application (e.g. thunderbird, nemo, soffice.bin) via tty brings gdm3 to life again. The funny thing is that when e.g. I open a link via thunderbird and gdm3 freezes, then I kill thunderbird via tty and switch back to X, then thunderbird is gone but firefox has opened the link.

I activated gdm3 debug output but could not find anything (I'm not an ubuntu/X/gdm expert).
One freeze occurs somewhere between two **systemd-logind: got pause for 13:73** in syslog_gdm3.log

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: gdm3 3.36.3-0ubuntu0.20.04.4
ProcVersionSignature: Ubuntu 5.4.0-81.91-generic 5.4.128
Uname: Linux 5.4.0-81-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.18
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Thu Sep 2 12:23:57 2021
InstallationDate: Installed on 2018-07-26 (1134 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
ProcEnviron:
 LANGUAGE=de_CH:de
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_CH.UTF-8
 SHELL=/bin/bash
SourcePackage: gdm3
UpgradeStatus: Upgraded to focal on 2020-10-07 (329 days ago)
mtime.conffile..etc.gdm3.custom.conf: 2021-09-02T11:47:52.516792

[Daniel van Vugt (vanvugt)]

gdm3 doesn't have a GUI so reassigning to gnome-shell that provides all the related GUIs.

[Daniel van Vugt (vanvugt)]

Thanks for the bug report. Please:

1. Run this command to send us additional info:

   apport-collect 1942432

2. Check for crashes that might be causing shell freezes using these instructions:

   https://wiki.ubuntu.com/Bugs/Responses#Missing_a_crash_report_or_having_a_.crash_attachment

[Nicolas Herzog (klaus-jean-duke)]

Thank you for the quick response.
I'm sorry for the work I generated. After reporting the bug, I tried another display / window manager, respectively, and managed my system into a non-working GUI.
I then did a backup and reinstalled Linux, now cinnamon is working well.
So you can close the bug in my view.