https://bugzilla.kernel.org/show_bug.cgi?id=206987
--- Comment #24 from Cyrax (evvke@hotmail.com) --- (In reply to Petteri Aimonen from comment #16)
I hit the same issue, using Ubuntu 20.04. It happened when switching window to Firefox. For me it only crashed Xorg, ssh to the machine still worked ok. Killing Xorg didn't work and `shutdown -r now` hung up somewhere.
Here is a bug report on the Ubuntu package: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1881134
Here is call trace decoded with the debug symbols:
[clip]
Yeah, it happens when switching windows and/or to different workspace. And yes it will crash Xorg only, other things will continue work as usual and issuing reboot command via SSH won't - well - reboot it. Only REISUB brings machine back to usable state.