gstreamer stopped working for me recently, and the cause is a "hung GPU", as
outlined by the following error messages:

[30911.904245] [drm] GPU HANG: ecode 7:0:0x00200000, in MediaPl~back #3 [2287], reason: Ring hung, action: reset
[30911.904364] [drm:i915_set_reset_status [i915]] *ERROR* gpu hanging too fast, banning!
[30911.906429] drm/i915: Resetting chip after gpu hang

The interesting bit is that it happens only when using the vaapi sink via
gstreamer1.0-vaapi (gstreamer-1.0-x works normally). This seem to have started
with libva1 1.6.0-1, although I cannot confirm.

By comparison, mplayer -vo=vaapi doesn't seem to trigger the issue.

Of course, it doesn't hide that fact that the userland can kill the GPU, but
maybe it helps debugging.

iceweasel is similarly affected, so playing any external h264 source with
gstreamer enabled might result in an unresponsive system (and probably worse).