That problem is believed to be caused by an Intel GPU lockup
This may be caused either by an unrelated GPU lockup (then it's a driver problem) or a fauty X grab. If it's caused by an X grab, you should be able to intercept input by pressing "Alt + SysRq + R" and then switch to console with "Alt + F1". If that has no effect, you're probably hitting a GPU lockup.
That problem is believed to be caused by an Intel GPU lockup
This may be caused either by an unrelated GPU lockup (then it's a driver problem) or a fauty X grab. If it's caused by an X grab, you should be able to intercept input by pressing "Alt + SysRq + R" and then switch to console with "Alt + F1". If that has no effect, you're probably hitting a GPU lockup.