how about 16.04? It does not hang any more, but the message is still repeated many times in the dmesg log:

[    1.940071] ------------[ cut here ]------------
[    1.940109] WARNING: CPU: 1 PID: 6 at /build/linux-Ay7j_C/linux-4.4.0/drivers/gpu/drm/drm_irq.c:1326 drm_wait_one_vblank+0x1b5/0x1c0 [drm]()
[    1.940113] vblank wait timed out on crtc 0
[    1.940116] Modules linked in: hid_generic usbhid hid i915 psmouse ahci i2c_algo_bit firewire_ohci libahci sdhci_pci pata_acpi sdhci firewire_core drm_kms_helper crc_itu_t syscopyarea sysfillrect ssb sysimgblt fb_sys_fops sky2 drm wmi fjes video
[    1.940155] CPU: 1 PID: 6 Comm: kworker/u4:0 Not tainted 4.4.0-21-generic #37-Ubuntu
[    1.940158] Hardware name: Dell Inc. Inspiron 1525                   /0U990C, BIOS A17 10/27/2009
[    1.940166] Workqueue: events_unbound async_run_entry_fn
[    1.940171]  0000000000000286 00000000601d6afd ffff8800bb7f7a08 ffffffff813e93c3
[    1.940177]  ffff8800bb7f7a50 ffffffffc0058b10 ffff8800bb7f7a40 ffffffff81080f62
[    1.940188]  ffff880035df3800 0000000000000000 0000000000000000 0000000000000003
[    1.940191] Call Trace:
[    1.940197]  [<ffffffff813e93c3>] dump_stack+0x63/0x90
[    1.940202]  [<ffffffff81080f62>] warn_slowpath_common+0x82/0xc0
[    1.940204]  [<ffffffff81080ffc>] warn_slowpath_fmt+0x5c/0x80
[    1.940209]  [<ffffffff810c3575>] ? finish_wait+0x55/0x70
[    1.940224]  [<ffffffffc00292a5>] drm_wait_one_vblank+0x1b5/0x1c0 [drm]
[    1.940227]  [<ffffffff810c3a10>] ? wake_atomic_t_function+0x60/0x60
[    1.940285]  [<ffffffffc0208339>] intel_get_load_detect_pipe+0x529/0x530 [i915]
[    1.940325]  [<ffffffffc02418ed>] intel_tv_detect+0x13d/0x5f0 [i915]
[    1.940341]  [<ffffffffc00e7da5>] drm_helper_probe_single_connector_modes_merge_bits+0x235/0x4d0 [drm_kms_helper]
[    1.940349]  [<ffffffffc00e8053>] drm_helper_probe_single_connector_modes+0x13/0x20 [drm_kms_helper]
[    1.940358]  [<ffffffffc00f491e>] drm_fb_helper_initial_config+0xae/0x420 [drm_kms_helper]
[    1.940396]  [<ffffffffc02184bb>] intel_fbdev_initial_config+0x1b/0x20 [i915]
[    1.940399]  [<ffffffff810a2f28>] async_run_entry_fn+0x48/0x150
[    1.940402]  [<ffffffff81099ff2>] process_one_work+0x162/0x480
[    1.940405]  [<ffffffff8109a35b>] worker_thread+0x4b/0x4c0
[    1.940408]  [<ffffffff8109a310>] ? process_one_work+0x480/0x480
[    1.940411]  [<ffffffff810a0528>] kthread+0xd8/0xf0
[    1.940414]  [<ffffffff810a0450>] ? kthread_create_on_node+0x1e0/0x1e0
[    1.940418]  [<ffffffff8182488f>] ret_from_fork+0x3f/0x70
[    1.940420]  [<ffffffff810a0450>] ? kthread_create_on_node+0x1e0/0x1e0
[    1.940423] ---[ end trace f06ce4fed187d576 ]---
[    1.946160]  sda: sda1 sda2 sda3 sda4 < sda5 sda6 sda7 sda8 sda9 >
[    1.947069] sd 2:0:0:0: [sda] Attached SCSI disk
[    2.016251] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x39834d15f18, max_idle_ns: 881590752306 ns
[    2.072400] firewire_core 0000:02:09.0: created device fw0: GUID 444fc0000d6981e1, S400
[    2.084258] ------------[ cut here ]------------
[    2.084291] WARNING: CPU: 1 PID: 6 at /build/linux-Ay7j_C/linux-4.4.0/drivers/gpu/drm/drm_irq.c:1326 drm_wait_one_vblank+0x1b5/0x1c0 [drm]()
[    2.084295] vblank wait timed out on crtc 0
[    2.084297] Modules linked in: hid_generic usbhid hid i915 psmouse ahci i2c_algo_bit firewire_ohci libahci sdhci_pci pata_acpi sdhci firewire_core drm_kms_helper crc_itu_t syscopyarea sysfillrect ssb sysimgblt fb_sys_fops sky2 drm wmi fjes video
[    2.084333] CPU: 1 PID: 6 Comm: kworker/u4:0 Tainted: G        W       4.4.0-21-generic #37-Ubuntu
[    2.084337] Hardware name: Dell Inc. Inspiron 1525                   /0U990C, BIOS A17 10/27/2009
[    2.084344] Workqueue: events_unbound async_run_entry_fn
[    2.084348]  0000000000000286 00000000601d6afd ffff8800bb7f7938 ffffffff813e93c3
[    2.084354]  ffff8800bb7f7980 ffffffffc0058b10 ffff8800bb7f7970 ffffffff81080f62
[    2.084360]  ffff880035df3800 0000000000000000 0000000000000000 0000000000000005
[    2.084365] Call Trace:
[    2.084378]  [<ffffffff813e93c3>] dump_stack+0x63/0x90
[    2.084382]  [<ffffffff81080f62>] warn_slowpath_common+0x82/0xc0
[    2.084384]  [<ffffffff81080ffc>] warn_slowpath_fmt+0x5c/0x80
[    2.084388]  [<ffffffff810c3575>] ? finish_wait+0x55/0x70
[    2.084403]  [<ffffffffc00292a5>] drm_wait_one_vblank+0x1b5/0x1c0 [drm]
[    2.084406]  [<ffffffff810c3a10>] ? wake_atomic_t_function+0x60/0x60
[    2.084452]  [<ffffffffc0202052>] intel_pre_disable_primary+0x52/0x80 [i915]
[    2.084491]  [<ffffffffc0202287>] intel_pre_plane_update+0x107/0x140 [i915]
[    2.084530]  [<ffffffffc0202800>] intel_atomic_commit+0xf0/0x6f0 [i915]
[    2.084549]  [<ffffffffc004280e>] ? drm_atomic_check_only+0x18e/0x590 [drm]
[    2.084569]  [<ffffffffc0042cf0>] ? drm_atomic_set_fb_for_plane+0x20/0x90 [drm]
[    2.084588]  [<ffffffffc0042c47>] drm_atomic_commit+0x37/0x60 [drm]
[    2.084626]  [<ffffffffc0208460>] intel_release_load_detect_pipe+0x120/0x160 [i915]
[    2.084666]  [<ffffffffc0241aeb>] intel_tv_detect+0x33b/0x5f0 [i915]
[    2.084677]  [<ffffffffc00e7da5>] drm_helper_probe_single_connector_modes_merge_bits+0x235/0x4d0 [drm_kms_helper]
[    2.084685]  [<ffffffffc00e8053>] drm_helper_probe_single_connector_modes+0x13/0x20 [drm_kms_helper]
[    2.084694]  [<ffffffffc00f491e>] drm_fb_helper_initial_config+0xae/0x420 [drm_kms_helper]
[    2.084733]  [<ffffffffc02184bb>] intel_fbdev_initial_config+0x1b/0x20 [i915]
[    2.084736]  [<ffffffff810a2f28>] async_run_entry_fn+0x48/0x150
[    2.084739]  [<ffffffff81099ff2>] process_one_work+0x162/0x480
[    2.084742]  [<ffffffff8109a35b>] worker_thread+0x4b/0x4c0
[    2.084745]  [<ffffffff8109a310>] ? process_one_work+0x480/0x480
[    2.084747]  [<ffffffff810a0528>] kthread+0xd8/0xf0
[    2.084750]  [<ffffffff810a0450>] ? kthread_create_on_node+0x1e0/0x1e0
[    2.084754]  [<ffffffff8182488f>] ret_from_fork+0x3f/0x70
[    2.084757]  [<ffffffff810a0450>] ? kthread_create_on_node+0x1e0/0x1e0
[    2.084759] ---[ end trace f06ce4fed187d577 ]---
[    2.184216] ------------[ cut here ]------------
[    2.184244] WARNING: CPU: 1 PID: 6 at /build/linux-Ay7j_C/linux-4.4.0/drivers/gpu/drm/drm_irq.c:1326 drm_wait_one_vblank+0x1b5/0x1c0 [drm]()
[    2.184247] vblank wait timed out on crtc 0
[    2.184249] Modules linked in: hid_generic usbhid hid i915 psmouse ahci i2c_algo_bit firewire_ohci libahci sdhci_pci pata_acpi sdhci firewire_core drm_kms_helper crc_itu_t syscopyarea sysfillrect ssb sysimgblt fb_sys_fops sky2 drm wmi fjes video
[    2.184282] CPU: 1 PID: 6 Comm: kworker/u4:0 Tainted: G        W       4.4.0-21-generic #37-Ubuntu
[    2.184285] Hardware name: Dell Inc. Inspiron 1525                   /0U990C, BIOS A17 10/27/2009
[    2.184290] Workqueue: events_unbound async_run_entry_fn
[    2.184294]  0000000000000286 00000000601d6afd ffff8800bb7f7958 ffffffff813e93c3
[    2.184299]  ffff8800bb7f79a0 ffffffffc0058b10 ffff8800bb7f7990 ffffffff81080f62
[    2.184305]  ffff880035df3800 0000000000000000 0000000000000000 0000000000000005
[    2.184310] Call Trace:
[    2.184316]  [<ffffffff813e93c3>] dump_stack+0x63/0x90
[    2.184320]  [<ffffffff81080f62>] warn_slowpath_common+0x82/0xc0
[    2.184325]  [<ffffffff81080ffc>] warn_slowpath_fmt+0x5c/0x80
[    2.184330]  [<ffffffff810c3575>] ? finish_wait+0x55/0x70
[    2.184354]  [<ffffffffc00292a5>] drm_wait_one_vblank+0x1b5/0x1c0 [drm]
[    2.184360]  [<ffffffff810c3a10>] ? wake_atomic_t_function+0x60/0x60
[    2.184409]  [<ffffffffc01fcf9f>] i9xx_crtc_disable+0x3f/0x450 [i915]
[    2.184447]  [<ffffffffc01f4f8c>] ? intel_crtc_disable_planes+0xdc/0xf0 [i915]
[    2.184486]  [<ffffffffc0202820>] intel_atomic_commit+0x110/0x6f0 [i915]
[    2.184506]  [<ffffffffc004280e>] ? drm_atomic_check_only+0x18e/0x590 [drm]
[    2.184525]  [<ffffffffc0042cf0>] ? drm_atomic_set_fb_for_plane+0x20/0x90 [drm]
[    2.184544]  [<ffffffffc0042c47>] drm_atomic_commit+0x37/0x60 [drm]
[    2.184582]  [<ffffffffc0208460>] intel_release_load_detect_pipe+0x120/0x160 [i915]
[    2.184622]  [<ffffffffc0241aeb>] intel_tv_detect+0x33b/0x5f0 [i915]
[    2.184631]  [<ffffffffc00e7da5>] drm_helper_probe_single_connector_modes_merge_bits+0x235/0x4d0 [drm_kms_helper]
[    2.184639]  [<ffffffffc00e8053>] drm_helper_probe_single_connector_modes+0x13/0x20 [drm_kms_helper]
[    2.184648]  [<ffffffffc00f491e>] drm_fb_helper_initial_config+0xae/0x420 [drm_kms_helper]
[    2.184686]  [<ffffffffc02184bb>] intel_fbdev_initial_config+0x1b/0x20 [i915]
[    2.184689]  [<ffffffff810a2f28>] async_run_entry_fn+0x48/0x150
[    2.184692]  [<ffffffff81099ff2>] process_one_work+0x162/0x480
[    2.184695]  [<ffffffff8109a35b>] worker_thread+0x4b/0x4c0
[    2.184698]  [<ffffffff8109a310>] ? process_one_work+0x480/0x480
[    2.184700]  [<ffffffff810a0528>] kthread+0xd8/0xf0
[    2.184703]  [<ffffffff810a0450>] ? kthread_create_on_node+0x1e0/0x1e0
[    2.184706]  [<ffffffff8182488f>] ret_from_fork+0x3f/0x70
[    2.184709]  [<ffffffff810a0450>] ? kthread_create_on_node+0x1e0/0x1e0
[    2.184711] ---[ end trace f06ce4fed187d578 ]---