Horizontal scroll over dock causes it to crash and disappear, and a temporary GUI freeze

[Jani Uusitalo]

# Steps to reproduce
0. have a mouse with horizontal scrolling functionality (mine is a Microsoft Comfort Mouse 4500 with a tilting action for horizontal scroll)
1. move mouse pointer over the dock
2. use the mouse scroller to scroll horizontally

# What I expect to happen
Nothing

# What happens
Mouse pointer and everything on screen freezes. After a few seconds it unfreezes, but all the icons from the dock are missing. I have to log out and back in to restore the dock.

# Other info
Slightly similar to LP #1875106, but I'm not using imwheel.

I am using Wayland.

Syslog seems to always point to this one function: "The offending callback was get_preferred_height(), a vfunc". I'll attach the relevant part from one crash.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: gnome-shell-extension-ubuntu-dock 68ubuntu1~20.04.1
ProcVersionSignature: Ubuntu 5.8.0-53.60~20.04.1-generic 5.8.18
Uname: Linux 5.8.0-53-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu27.18
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Mon May 31 20:35:37 2021
InstallationDate: Installed on 2020-11-30 (182 days ago)
InstallationMedia: Ubuntu 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
PackageArchitecture: all
SourcePackage: gnome-shell-extension-ubuntu-dock
UpgradeStatus: No upgrade log present (probably fresh install)
modified.conffile..etc.default.apport: [modified]
mtime.conffile..etc.default.apport: 2020-11-30T20:24:48.587084

[Daniel van Vugt (vanvugt)]

Thanks but I'm not sure that section of log is relevant here. And even if it is, there's not enough information so...

Thank you for taking the time to report this bug and helping to make Ubuntu better. It sounds like some part of the system has crashed. To help us find the cause of the crash please follow these steps:

1. Look in /var/crash for crash files and if found run:
    ubuntu-bug YOURFILE.crash
Then tell us the ID of the newly-created bug.

2. If step 1 failed then look at https://errors.ubuntu.com/user/ID where ID is the content of file /var/lib/whoopsie/whoopsie-id on the machine. Do you find any links to recent problems on that page? If so then please send the links to us.

3. If step 2 also failed then apply the workaround from bug 994921, reboot, reproduce the crash, and retry step 1.

Please take care to avoid attaching .crash files to bugs as we are unable to process them as file attachments. It would also be a security risk for yourself.

[Jani Uusitalo (uusijani)]

1. There's nothing in /var/crash
2. There are no reports on the page for this computer.
3. Done, still nothing in /var/crash.

I don't know if this means it's not a true crash, although visually all the indications are there.

I also verified that this reproduces when using a newly-created user (with the only change from defaults for it being switching to Wayland), and also on another computer (also running 20.04). I am limited to using the one mouse that I have, so that all testing so far has been with the same mouse.

[Daniel van Vugt (vanvugt)]

OK, next time the crash happens please:

1. Wait 10 seconds.

2. Log in again.

3. Run:

   journalctl -b0 > journal.txt
   journalctl -b-1 > prevboot.txt

4. Attach the resulting text files here.

[Jani Uusitalo (uusijani)]

I can reproduce the crash at will with the steps I listed above, so I don't have to wait for it to happen. It also doesn't forcibly log me out, so I can enter those commands by just having a terminal window present when I trigger the issue. But I logged out here (after triggering) anyway since you instructed me to log in, in case it matters.

Also, there's lots of noise in these from Boinc, thanks to #1876313.

[Daniel van Vugt (vanvugt)]

Thanks. I can't yet see a crash, and I don't have the hardware to reproduce the issue, but I can see that you have a number of unsupported extensions. So first please try disabling (in the Extensions app) or uninstalling all but the three default Ubuntu extensions. Then log in again.

[Jani Uusitalo (uusijani)]

Do you want another log for that? Because (as I already mentioned above), this also reproduces when using a newly-created user, so that means no unsupported extensions.

[Daniel van Vugt (vanvugt)]

Maybe next you should try gnome-shell-extension-dashtodock (turn off Ubuntu Dock during that) and if the same bug happens there then report it to the developers at https://github.com/micheleg/dash-to-dock

[Jani Uusitalo (uusijani)]

There's no gnome-shell-extension-dashtodock package for focal [1], but I did try with Dash to Dock from extensions.gnome.org, and could not reproduce the issue with it. I tried with the default settings, as well as after recreating the look & feel of Ubuntu Dock as much as possible.

Dash to Dock has customizable action for the scroll (to either switch workspaces or windows, or to do nothing), and all of those also worked just as expected.

I also noticed that using the two finger scroll function of the touchpad on my laptop does *not* trigger this (whereas using the mouse on it does).

* [1] https://packages.ubuntu.com/search?keywords=gnome-shell-extension-dashtodock