X.org freeze after selecting nvidia profile on Plasma Desktop

[Luca Osvaldo Mastromatteo]

- Using ubuntu 18.04.2 LTS, also tried 19.10 development eoan edition.
- Tried driver NVIDIA 390 + 430 from the repo, same result
- Happens only on KDE Plasma desktop
- Does not happen on GNOME desktop
- Used the X server settings instead of the CLI

Reproducibility: 75%

Steps required:
- Installing nvidia drivers on an optimus laptop
- Rebooting
- Select NVIDIA GPU with prime from Intel
- Waiting some seconds
- Opening NVIDIA X server settings again TWICE, increases a lot the chance of the freeze to happen (looks like it gets the nvidia module loaded even before the session logout)

Bug observed:
- Before the nvidia module gets loaded (I could type lsmod | grep nvidia fine and no module is loaded after the first 3 seconds)
- When (presumably) the nvidia driver is loaded (checked from a tty), the X.org session locks up. The mouse cursor can move things, but cannot click anything, everything else on the screen is frozen up

Workaround: Killing the X.org session gives an usable graphical system

Notes: If the session ends (doing a logout so SDDM) before the nvidia module gets loaded, there is no lockup at all, but once the nvidia driver is loaded, it looks like it's when the issue appears.

[Luca Osvaldo Mastromatteo (lukycrociato)]

To be more clear, it looks like what actually freezes is the plasma panel itself, you could always use the alt+tab hotkey to switch programs
You could also restart plasmashell. It happens right when the Nvidia module got loaded before logging off

[Luca Osvaldo Mastromatteo (lukycrociato)]

#1 doesn't happen to be always the case, most of the times the desktop become unusuable.

Anyway, with further testing I updated the bug.

Looks like related to the X server settings.

Opening it TWICE after selecting the NVIDIA card from intel, triggers this behavior.