Created attachment 160441 [details]
Backtrace of frozen kwin_x11

SUMMARY
Starting krunner causes kwin to freeze on X11.


STEPS TO REPRODUCE
1a. start krunner - (tried per shortcut or konsole; makes no difference)
or
1b. start systemsettings and navigate to "Display and Monitor" -> Compositor

OBSERVED RESULT
Everything visible except the mouse cursor freezes. (Sound is not affected)
The mouse cursor also continues to change depending on item in the background. Waiting cursor is still animated.

After kwin restarts (by switching to text console; then back to X11 and wait a few seconds):
krunner works normal
the compositor kcm is a black rectangle and stays that way even if compositing is disabled.

Both work fine if compositing is disabled before start.
Problem does not occurr in wayland-session.

EXPECTED RESULT
No freeze

SOFTWARE/OS VERSIONS
Linux Distro: KDE Neon
KDE Plasma Version: 5.27.6
KDE Frameworks Version: 5.108.0
Qt Version: 5.15.10

ADDITIONAL INFORMATION
GPU: NVIDIA GeForce GTX 1060 6GB/PCIe/SSE2
NVidia driver: 535.54.03
Kernel: 6.1.0-1016-oem (happens with 6.1.0-1015-oem as well)


MORE DETAILS:
This started after upgrading some packages (not sure which, but I assume kwin_x11 was among them) a few days ago.

At first I thought this might be related to #338355, but there are too many differences in the freeze description:

Also true here:
> - Entire desktop image is frozen
> - Pointer still works
> - Does not happen if compositing is disabled
> - Does not happen on Wayland (But too many other things don't work for me)

NOT true here:
> - Pointer still operates on desktop under frozen image (more on that below)
>   - If during the freeze, I tried to operate on any windows with pointer, they now show up in updated positions/sizes, etc.
> - Does not happen on kernels older than 6.1.9 
> - Does not happen if compositing is toggled off then on after logging in
> - Does not happen a 2nd time if kwin is killed and restarted

In case of the kernel version, that is assuming ubuntu kernel versioning matches upstream.

I followed the steps mentioned in #338355 to produce a backtrace which indicates a different cause.