Comment 74 for bug 1384342

Same issue occured on Ubuntu 14.04 LTS after upgrading kernel to 3.16, and Xorg (LTS hardware enablement program). Screen was frozen, but I was able to recover by switching to a VT and restarting X (switching eventually worked after a long delay). Never any problems of this sort with the 3.13-kernel. (Intel HD 4000 "Ivy Bridge").

[79486.195054] WARNING: CPU: 0 PID: 1751 at /build/buildd/linux-lts-utopic-3.16.0/drivers/gpu/drm/i915/intel_display.c:3324 intel_crtc_wait_for_pending_flips+0x171/0x180 [i915]()