Comment 25 for bug 404331

A little more information in case it gives any clues:

As well as the 3 scenarios above (triggering under identical conditions as far as I can see), there is a fourth after all:

d) As a) but the screen blanks. That is, there is a momentary pause, the screen goes entirely black, but I am able to (say) Ctrl+Alt+F1, llogin and sudo reboot.

So the screen blanking is a random event happening in about 25% of cases. Type a) is probably more common than the others.

I'm attaching a drawing of what the might happen to the scrollbar in the application window when the freeze happens. There are black horizonal bars across the scrollbar, with a further few white pixels immediately below, and sometimes the status line is corrupted. As I mention, any screenshot I can produce is corrupted.

If I restart gdm (and/or X) from the console after the freeze, I get the fade into the greeter background (the brown ubuntu spotlight) but the login dialogue is not drawn (usually that space is occupied by a faded version of whatever was on the screen before the gdm restart). So it's similar to the situation after the freeze in a) before restarting gdm: the background is drawn correctly, but any other windows cannot be written. I'm pretty sure that if I could change the video mode (to text, say, and back again), gdm would display correctly. Is there any way to do this - resizecons or xvidtune don't seem to help?

If I comment the Option "DRI" "false" workaround (which seemed to work for lucid), and enable Compiz, visual effects seem to work correctly until the freeze. It's fairly easy now to reproduce a freeze: turn visual effects no normal or high, visit a page like this in Epiphany and scroll down - I can scroll down a page or two before the freeze. Also, when this happens it seems Compiz crashes because the title bars disappear.

Very little is logged about the problem in Xorg.0.log (I've just added -logverbose to
/etc/X11/xinit/xserverrc in case that helps.)

Once it's got into this state (a), switching with Ctrl+Alt and back again to the frozen Xorg gives:

(II) AIGLX: Suspending AIGLX clients for VT switch
[dix] couldn't enable device 9
[dix] couldn't enable device 9
[dix] couldn't enable device 9
[dix] couldn't enable device 9
[dix] couldn't enable device 9
(II) Open ACPI successful (/var/run/acpid.socket)
(II) AIGLX: Resuming AIGLX clients after VT switch

but of course I'm still in the state of having X frozen with only the cursor working.