I'm having trouble with my X session locking up apparently at random. Everything stops responding except the mouse pointer. I can exit to a tty, but the screen goes blank for around 60s before anything appears. When it finally does I get the see the following error:
kernel: [ some number] [drm:intel_pipe_set_base] ERROR pipe is still busy with an old pageflip
From there I have tried killing recent processes, but to no avail. When I switch back to the x-session there is the same ~60s delay before anything comes up and again every time I go back to tty. I can restart the session with a ctrl-alt-backspace, not ideal since it seems like it could be recoverable.
Closest thing to my problem that I've found is this post https://bugs.freedesktop.org/show_bug.cgi?id=82612 but I wanted to make sure it's the right thing before randomly updating my kernel or intel drivers.
Lenovo X1 Carbon, Ubuntu 14.04 LTS x86_64, some standard intel graphics chip, running with the laptop's screen + an external screen off the mini-dp.
Glad to provide more info if needed.
ps already posted this q here http://ubuntuforums.org/showthread.php?t=2272031