Bug 456625

SUMMARY
This bug is way too nasty :(
Some people have hard time to reproduce it and reporting it. I figured out how to freeze KDE Plasma every time. (reproducable KDE Freeze). After invesigation I did it a few times and KDE freezes totally every time.

What happens:
Keys on keyboard are intercepted you can't use mouse to close a window. You can't restart system because keyboard DEOSN'T (ctrl+alt+del to see logout/shutdown menu) RESPOND, you can't go through new start menu: you can open it but clicking shutdown/restart (& small button to logout) DOES NOT work. Nothing is clickable. Connecting new mouse instead of using touchpad doesn't help at all. Its the same effect. Can't use keyboard either. 


It MAY BE (not sure) similar to bug:
https://bugs.kde.org/show_bug.cgi?id=420157
and maybe fee other random freezes reported here, that are very difficult to track it down.

==> I figured out what the cultprit is. Here are the steps to fully reproduce it:

1. Fresh login
2. open these apps: Kate, meta+E, Konsole, gimp, falkon, firefox (use krunner to do it quickly)
3. Use alt+tab intensively to be sure, until you get Kate again (also use arrows this way and other way)
4. Click "Restore" (next to close and minimize, aka unmaximize)
5. use alt+right click inside Kate. Click white space in Kate to clear this context menu.  Now, use Meta+ (fn) PgUp to maximize window.
6. Now try to type in Kate.
7. Now try to close kate, try to use alt+tab, try to restart the system either using ctrl+alt+del to get you to the shutdown/logout screen or try to shutdown via start menu. Total freeze. You have to hard reset the whole computer.

THE CULPRIT IS THE SHORTCUT META+PgUP to maximize window. So far I have no freezes after deleting the shortcut and changing it to ... META+M. (I know its weired...).

This is a nasty bug. If someone has freezezes, can't click intercepted, keyboard (on non exotic graphics, xorg,libinput, etc.) they can try deleting this shortcut and maybe alt+tab and everyghing will be OK. So far so good on my system.


Technical info:
This is not nvidia nor AMD APU. nor wayland. Its pure intel skylyke, generic, xorg, libinput and latest updated arch. It happens on the few last iterations of KDE after kwin rewrite regardless of alt+tab plugins present or not, regardless of which plugins for alt+tab used (now a separate library to get cover or flip switch, happens on breeze too without plugins).


OBSERVED RESULT


EXPECTED RESULT
NO Freezes, keboard freeze, libinput freeze with new rewritten Kwin.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: Arch
(available in About System)
KDE Plasma Version: Few last iterations: ..., 5.22, 5.23
KDE Frameworks Version: Few last iterations, 5.9x, ..., 5.96
Qt Version: 5.15.5

ADDITIONAL INFORMATION
Pure Intel Skylyke, Xorg, libinput, No nvidia, no wayland, no AMD APU.