When running the igt@kms_busy@extended-modeset-hang-newfb* tests on Sandybrige, we consistently hit the following issue:

[   49.763465] i915 0000:00:02.0: Resetting chip after gpu hang
[   60.894990] asynchronous wait on fence i915:[global]:201 timed out
[   60.933406] [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe B FIFO underrun
[   60.933613] [drm:intel_set_pch_fifo_underrun_reporting [i915]] *ERROR* uncleared pch fifo underrun on pch transcoder B
[   60.933648] [drm:intel_pch_fifo_underrun_irq_handler [i915]] *ERROR* PCH transcoder B FIFO underrun

Full logs:
 - https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_2993/shard-snb6/igt@kms_busy@extended-modeset-hang-newfb-with-reset-render-A.html
 - https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_2993/shard-snb5/igt@kms_busy@extended-modeset-hang-newfb-with-reset-render-B.html
 - https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_2993/shard-snb4/igt@kms_busy@extended-modeset-hang-newfb-render-A.html
 - https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_2993/shard-snb5/igt@kms_busy@extended-modeset-hang-newfb-render-B.html