Enabling Plasma widgets causes hard freezes

[John361]

Leap 15.5.
Hardware acceleration enabled (Mesa-dri-nouveau)
Graphics card nVidia GeForce 8400GS; tested also on a GeForce 320M for laptops. Both cards are fully supported by nouveau.
Everything works fine and the system is perfectly stable, with or without Wayland. If I try to enable some Plasma widgets, after a few seconds the whole system freezes; more precisely, it happens with widgets that display text (for example, network speed or disk activity). The only way to fix this is by pressing the power button.
Same problem with other recent distributions (KDE Neon 6.x, Kubuntu, etc).

This is what happens before the crash:

[susejunky]

@John361

The only way to fix this is by pressing the power button.

So this happens when you are using X11?

Did you try to restart the X server by pressing Ctrl+Alt+Backspace twice?

[John361]

It is a hard freeze. Everything is blocked; mouse, keyboard, etc. Nothing works.

[susejunky]

When you restart your system (after you were forced to switch it off) and check the journal with

journalctl --boot=-1 --priority=3

(you need to do this as “root” or with a user who is member of the group “systemd-journal”)

can you see any errors reported?

[John361]

journalctl --boot=-1 --priority=3

is a long sequence of:

nouveau: TRAP_PROP - TP 1 Unknown CUDA fault at address .....
plasma-systemmo[2547] .......
trapped read at ...... on channel 21

and

nouveau: TRAP_TEXTURE TP TP1 [FAULT]
plasma_systemmo[2547]
trapped read at ..... on channel 21