Affected machines: snb-dellxps, seems to blow up every 10-20 runs. Somehow the vblank wait in atomic_commit goes boom. Most easily reproduced with

/igt@kms_pipe_crc_basic@hang-read-crc-pipe-*

Full backtrace

[  105.995009] ------------[ cut here ]------------
[  105.995034] WARNING: CPU: 1 PID: 6024 at drivers/gpu/drm/i915/intel_display.c:13530 intel_atomic_commit+0x1271/0x1400 [i915]
[  105.995035] pipe A vblank wait timed out
[  105.995036] Modules linked in: snd_hda_intel i915 smsc75xx usbnet mii x86_pkg_temp_thermal intel_powerclamp coretemp snd_hda_codec_hdmi crct10dif_pclmul crc32_pclmul ghash_clmulni_intel snd_hda_codec_realtek snd_hda_codec_generic snd_hda_codec lpc_ich snd_hwdep snd_hda_core mei_me snd_pcm mei broadcom bcm_phy_lib tg3 ptp pps_core [last unloaded: i915]
[  105.995053] CPU: 1 PID: 6024 Comm: kms_pipe_crc_ba Tainted: G     U          4.6.0-rc5-CI-CI_DRM_1270+ #1
[  105.995055] Hardware name: Dell Inc. XPS 8300  /0Y2MRG, BIOS A06 10/17/2011
[  105.995056]  0000000000000000 ffff8801239e3b28 ffffffff81405e55 ffff8801239e3b78
[  105.995058]  0000000000000000 ffff8801239e3b68 ffffffff81079c7c 000034dabf4c8560
[  105.995060]  0000000000000001 ffff8800c0b633f8 0000000000000000 0000000000000000
[  105.995063] Call Trace:
[  105.995067]  [<ffffffff81405e55>] dump_stack+0x67/0x92
[  105.995070]  [<ffffffff81079c7c>] __warn+0xcc/0xf0
[  105.995071]  [<ffffffff81079cea>] warn_slowpath_fmt+0x4a/0x50
[  105.995074]  [<ffffffff810c2e79>] ? finish_wait+0x59/0x70
[  105.995089]  [<ffffffffa0160051>] intel_atomic_commit+0x1271/0x1400 [i915]
[  105.995091]  [<ffffffff810c2fe0>] ? wait_woken+0x90/0x90
[  105.995093]  [<ffffffff81538ba2>] drm_atomic_commit+0x32/0x50
[  105.995095]  [<ffffffff8151587d>] drm_atomic_helper_set_config+0x7d/0xb0
[  105.995098]  [<ffffffff81527820>] drm_mode_set_config_internal+0x60/0x110
[  105.995099]  [<ffffffff8152c589>] drm_mode_setcrtc+0x199/0x500
[  105.995101]  [<ffffffff8151e95d>] drm_ioctl+0x13d/0x590
[  105.995102]  [<ffffffff8152c3f0>] ? drm_mode_setplane+0x1d0/0x1d0
[  105.995104]  [<ffffffff811ee15a>] do_vfs_ioctl+0x8a/0x670
[  105.995106]  [<ffffffff811f9fea>] ? __fget_light+0x6a/0x90
[  105.995108]  [<ffffffff811ee77c>] SyS_ioctl+0x3c/0x70
[  105.995110]  [<ffffffff817d2de9>] entry_SYSCALL_64_fastpath+0x1c/0xac
[  105.995111] ---[ end trace 393ccc6df884df73 ]---
[  115.777697] drm/i915: Resetting chip after gpu hang