Gnome high CPU preventing login after screen lock

[Fausto Marasco]

I have configured my PC to lock the screen automatically after a period of inactivity. Often when I come back to my PC I'm unable to login due to gnome shell running at 100% CPU (according to htop).

The only way I can log in is to SSH to the machine from another PC and kill the gnome shell task running at 100%

Other than noting this only happens when I try and unlock the screen I haven't been able to find any pattern which can explain this behaviour. I've never had problems with gnome shell while using the PC.

Some info about the machine Ubuntu 20.04, Nvidia drivers, 4k monitors

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: gnome-shell 3.36.4-1ubuntu1~20.04.2
ProcVersionSignature: Ubuntu 5.4.0-45.49-generic 5.4.55
Uname: Linux 5.4.0-45-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu27.8
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Mon Sep 7 22:01:37 2020
DisplayManager: gdm3
InstallationDate: Installed on 2020-09-05 (2 days ago)
InstallationMedia: Ubuntu 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
ProcEnviron:
 LANGUAGE=en_AU:en
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_AU.UTF-8
 SHELL=/bin/bash
RelatedPackageVersions: mutter-common 3.36.4-0ubuntu0.20.04.2
SourcePackage: gnome-shell
UpgradeStatus: No upgrade log present (probably fresh install)

[Daniel van Vugt (vanvugt)]

This looks like bug 1849142. To work around it just open the 'Extensions' app and disable 'Ubuntu AppIndicators'.

[Fausto Marasco (fausto.marasco)]

Daniel - I tried the work around recommended for bug 1849142 however that didn't fix the problem and the issue still persists.

I therefore believe that the issue is a separate one.
Are you able to provide any advice on the best place to collect gnome-shell logs?
I'm keen to assist in tracking down what ever information I can on this bug.

Thanks.

[Daniel van Vugt (vanvugt)]

To prove this isn't a duplicate of bug 1849142, please:

1. Open the 'Extensions' app and disable 'Ubuntu AppIndicators'.

2. Reboot.

3. Wait until the problem happens again.

4. When the problem happens next please run:

   journalctl -b0 > journal.txt

   and attach the resulting text file here.

[Fausto Marasco (fausto.marasco)]

Daniel - I had the issue happen a couple of times tonight. While the UI was unresponsive, I was able to use another machine to SSH to the PC and run the journalctl command you recommended.

The attached file journal6.txt contains 2 incidents one at around 17:49 and the other around 19:58

In both cases, I used HTOP to find the gnome-shell task running at 100% cpu then kill it. That fixes the problem and lets me log in again.

Please note that these logs were recorded with the AppIndicators extension turned back on. After still experiencing the problem with AppIndicators I turned it back on.

Let me know if you're prefer the journal file without AppIndicators on.

Appreciate your efforts in assisting to track down this issue.
Thanks.

[Daniel van Vugt (vanvugt)]

Yes, please do provide a log of the problem happening that doesn't contain "ubuntu-appindicators".

Please also try moving or removing this whole directory in case the cause is some other extension:

 ~/.local/share/gnome-shell/extensions

[Fausto Marasco (fausto.marasco)]

Daniel,
I disabeld the extensions and confirmed that the directory mentioned above is not present.

I am still experiencing the following.

After being away from my machine, I come back to find the screen locked as expected. The privacy settins are Blank screen display = 10 minutes & Automatic Screen Lock delay = 30 seconds.

When I move the mouse or hit a key to login, the machine is unresponive. After about 2-3 mins the login prompt will appear but still remains unresponsive.

I usually SSH to the machine using my ipad. With HTOP I find gnome-shell at 99% CPU or greater. If I kill the high CPU gnome-shell task I can login straight away. Sometimes after killing the gnome-shell it starts up again and goes stright to high CPU. If I kill it 4 or 5 times it usually then restarts with low/normal CPU usage.

The attached file journal16.txt was the result of the following command
journalctl -b0 > journal16.txt

This file contains 3 occurances of this behaviour at the following time stamps

Sept 14 16:28:29 logged in via ssh from ipad
Sept 14 16:28:46 killed gnome-sesion running with high CPU

Sept 14 18:19:25 logged in via ssh from ipad
Sept 14 18:19:38 killed gnome-sesion running with high CPU

Sept 14 19:19:00 logged in via ssh from ipad
Sept 14 19:19:12 killed gnome-sesion running with high CPU

[Daniel van Vugt (vanvugt)]

Thanks. I can't see anything obvious in that log.

Next please try disabling all Ubuntu extensions in the 'Extensions' app. Then log out and log in again. Because that log shows you do at least still have 'Ubuntu Dock' enabled.

[Fausto Marasco (fausto.marasco)]

Daniel,
after further extensive testing and trialling. I can confirm that the high CPU problem does not occur when I disable all GNOME extensions.
When no gnome-extensions were enabled the problem did not occur.

However, I was able to make the high CPU problem appear by running the dock gnome-extension.

I have noted a reduction in the frequency of this problem after the recent set of patches.

As you are already tracking a similar issue caused by gnome-extensions I am happy for you to close this ticket. However I am also willing to send you any further information if you want more data.

Regards,
Fausto.

[Daniel van Vugt (vanvugt)]

Do you mean the 'Ubuntu Dock' extension or some other dock?

Either way, I can't think of any existing bug for this. It wouldn't be bug 1849142.

[Launchpad Janitor (janitor)]

[Expired for gnome-shell-extension-ubuntu-dock (Ubuntu) because there has been no activity for 60 days.]