Created attachment 101212 [details]
/sys/class/drm/card0/error

Found the fololowing hang info in dmesg:

[665416.152274] [drm] stuck on render ring
[665416.152277] [drm] stuck on blitter ring
[665416.152802] [drm] GPU HANG: ecode 0:0xf4e9fffe, in Xorg [1291], reason: Ring hung, action: reset
[665416.152803] [drm] GPU hangs can indicate a bug anywhere in the entire gfx stack, including userspace.
[665416.152804] [drm] Please file a _new_ bug report on bugs.freedesktop.org against DRI -> DRM/Intel
[665416.152805] [drm] drm/i915 developers can then reassign to the right component if it's not a kernel issue.
[665416.152805] [drm] The gpu crash dump is required to analyze gpu hangs, so please always attach it.
[665416.152806] [drm] GPU crash dump saved to /sys/class/drm/card0/error
[665416.152868] [drm:i915_context_is_banned] *ERROR* gpu hanging too fast, banning!
[665418.152159] [drm] Enabling RC6 states: RC6 on, RC6p off, RC6pp off


This happened on Sandy Bridge I5-2400 with Linux 3.15, Xord 7.7 from Debian unstable 1:7.7+7 package. Uptime was 8 days and it's the first time I see this kind of error so it's not easily reproducible.

Some days ago I also got these in dmesg - maybe related, maybe not.
[168707.005151] [drm:ilk_display_irq_handler] *ERROR* Pipe A FIFO underrun
[168707.152144] [drm:ilk_display_irq_handler] *ERROR* Pipe A FIFO underrun