intel drmkms hang on shutdown

[Patrick Welche <prlw1%cam.ac.uk@localhost>]

On shutdown, usually, but not always, Xorg's cpu usage goes up to 100%,
and needs to be killed to allow shutdown to complete. I have seen this
with -current/amd64 on an ivy bridge, sandy bridge and pineview.
(Nearly popped in an Oxford comma there... ;-) )

Attaching to Xorg, a trace shows /usr/X11R7/lib/modules/drivers/intel_drv.so.

Thoughts?

Cheers,

Patrick