We are currently upgrading our NoMachine (NX) terminal servers to openSUSE Leap 15.6 (from 15.5) and found that when a Plasma session is started (via /usr/bin/startplasma-x11) and the user has a Plasma setting to start with an empty session (defined in ~/.config/ksmserverrc under the General section as: loginMode=emptySession), the session will start but will be mostly unresponsive. This is due to kwin_x11 using 100% CPU and the following is logged:
[ 09/30/2024 14:19:16.286 redirect_start FATAL ERROR ] Another composite manager is already running (and does not handle _NET_WM_CM_Sn correctly)
It will log this over and over until the partition runs out of space (100MB of logs in < 30 seconds).
If I disable compositor from starting at logon, this problem does not occur.
On a physical desktop without NX, using the same home directory (and therefore the same KDE Plasma settings), the session does not have this issue.
KDE Plasma went from 5.27.9 → 5.27.11 in this upgrade. The release notes do not show anything obvious.
So is it an llvmpipe issue (the virtual graphics driver that NX uses for headless sessions (I don’t experience the issue with a TigerVNC server which uses llvmpipe too) or is it an issue with the kwin_x11 compositor?
I am also reaching out to NoMachine about this considering I can’t reproduce it outside of NoMachine.