Bug 495122

SUMMARY
When I set my 4k screen to 120Hz, the system stops responding to keyboard/mouse and all screens are frozen. I cannot do Ctrl+Alt+F2 to switch to another VT. However I can be monitoring journalctl over ssh while this happens and there is no crash or error messages indicated, but it will not respond to initiate a new ssh connection. With that active ssh connection, if I try to kill kwin_wayland it will block and not respond. 

This is with an Nvidia RTX2080. If I swap that out for a Radeon RX6600, there are no issues.

Also I found that if I use kscreen-doctor and set the mode of all screens at once, it works fine only until I try to log out or change any screen mode again, where it will hang with the same behaviour as described above.

Frustratingly there is no segfault or crash data due to how it locks up.

STEPS TO REPRODUCE
1. Install RTX2080 as the only graphics card
2. start plasma wayland session
3. for the 4k screen, set it's refresh rate to 120Hz

OBSERVED RESULT
- system stops responding to keyboard/mouse and all screens are frozen
- `journalctl -f ` from an existing ssh connection doesn't show any errors
- trying to kill kwin_wayland over this ssh connection hangs
- cannot initiate new ssh connection
- If using kscreen-doctor instead of system settings gui, can succeed at setting the screen to 120Hz, but then the system will lock up in a similar way if you try to a) log out, b) change a screen mode again.

EXPECTED RESULT
system doesn't hang

SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 6.2.1
KDE Frameworks Version: 6.7.0
Qt Version: 6.8.0
Kernel Version: 6.6.57-1-lts (64-bit)
Graphics Platform: Wayland
Processors: 16 × Intel® Core™ i9-9900K CPU @ 3.60GHz
Memory: 62.7 GiB of RAM


ADDITIONAL INFORMATION
Maybe I can try attaching gdb to kwin_wayland over ssh before the lockup happens. Let me know if you have any ideas.