Created attachment 143306 [details]
Output of dmesg
Operating System: Arch Linux
KDE Plasma Version: 5.14.5
Qt Version: 5.12.1
KDE Frameworks Version: 5.54.0
Kernel Version: 4.20.6-arch1-1-ARCH
Graphics Card: NVIDIA GeForce GT 650M
Plasma locks up after splash screen, and it is sometimes (but not always) possible to switch to tty2 and kill the session using loginctl. The magic SysRq keys Alt+SysRq+REISUB and Alt+SysRq+REISUO always work though.
This seems to be a problem related to acceleration because adding the 'nouveau.noaccel=1' kernel parameter solves the problem, but disables some desktop effects as well.
Created attachment 143309 [details]
Part of pacman.log
The problem occurred after upgrading mesa from 18.3.2 to 18.3.3 and qt from 5.12.0 to 5.12.1, but downgrading mesa to 18.3.2 didn't help.
*** This bug has been marked as a duplicate of bug 109556 ***