Comment # 9 on bug 99236 from Michel Dänzer

Any chance you can bisect Mesa?

(In reply to Vitaly Ostrosablin from comment #8)
> But if that's mesa-only bug, shouldn't Ctrl+Alt+F1 work? Here GPU appears to
> have stopped output completely (most likely, fullscreen tty opens, but GPU
> shows same picture as on moment of freeze).

A GPU hang tends to cause the Xorg process to hang as well, which prevents VT
switching from working.