Comment 21 for bug 1275794

HW: Lenovo T440s with a Thinkpad Ultra Dock and a Dell U2410

The T440s was at the docking station when powering on.

If I start the X-server, plugin the Monitor to a DP connector at the docking station and call `xrandr --output DP2 --preferred` the X-server freezes. (Doesn't happen without the docking station at the mDP connector directly at the notebook.)

By freeze I mean:
- no cursor movement
- no VT switching

Though the maschine is reachable via ssh:
- X-server ignores `kill -9`

After 2 minutes the following kernel message shows up:
[ 480.195776] INFO: task kworker/0:1:34 blocked for more than 120 seconds.
[ 480.195779] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 480.195781] kworker/0:1 D 0000000000000246 0 34 2 0x00000000
[ 480.195803] Workqueue: events ironlake_panel_vdd_work [i915]
[ 480.195805] ffff880118cebd50 0000000000000046 0000000000014500 ffff880118cebfd8
[ 480.195809] ffff880118cebfd8 0000000000014500 ffff880119218870 ffff88011f214570
[ 480.195812] 0000000000000001 ffff880118cebcd8 ffffffff8109a884 ffff88011f2d4500
[ 480.195816] Call Trace:
[ 480.195822] [<ffffffff8109a884>] ? dequeue_entity+0x144/0x4d0
[ 480.195825] [<ffffffff81099815>] ? set_next_entity+0x95/0xb0
[ 480.195829] [<ffffffff810135a8>] ? __switch_to+0x118/0x4e0
[ 480.195833] [<ffffffff814e1029>] schedule+0x29/0x70
[ 480.195835] [<ffffffff814e1463>] schedule_preempt_disabled+0x23/0x30
[ 480.195839] [<ffffffff814df9d8>] __mutex_lock_slowpath+0x168/0x3b0
[ 480.195843] [<ffffffff814dfc32>] mutex_lock+0x12/0x30
[ 480.195852] [<ffffffffa060a8b5>] ironlake_panel_vdd_work+0x25/0x40 [i915]
[ 480.195855] [<ffffffff8107c6e7>] process_one_work+0x167/0x450
[ 480.195858] [<ffffffff8107d0f1>] worker_thread+0x121/0x3a0
[ 480.195861] [<ffffffff8107cfd0>] ? manage_workers.isra.23+0x2b0/0x2b0
[ 480.195865] [<ffffffff81083960>] kthread+0xc0/0xd0
[ 480.195868] [<ffffffff810838a0>] ? kthread_create_on_node+0x120/0x120
[ 480.195871] [<ffffffff814ea52c>] ret_from_fork+0x7c/0xb0
[ 480.195875] [<ffffffff810838a0>] ? kthread_create_on_node+0x120/0x120

The bug occured with
  o kernel 3.10.12
  o xorg 1.14.3
  o xf86-video-intel 2.11.15

For this test and the following logs it has been reproduced with
  o kernel 3.11.6
  o xorg 1.14.4
  o xf86-video-intel (at git head - dc61705 sna: Use an inplace exchange for large untiled BO).

A test with kernel 3.12 is in the queue.