Comment 39 for bug 749817

With today's natty updates, if the external monitor is connected, the machine crashes while booting, with this oops recorded:

Apr 10 17:47:45 joy kernel: [ 5.913652] BUG: unable to handle kernel NULL pointer dereference at 0000000000000230
Apr 10 17:47:45 joy kernel: [ 5.913701] IP: [<ffffffffa00fb4db>] intel_dp_link_down+0x32b/0x400 [i915]
Apr 10 17:47:45 joy kernel: [ 5.913752] PGD 23134d067 PUD 23134c067 PMD 0
Apr 10 17:47:45 joy kernel: [ 5.913779] Oops: 0000 [#1] SMP
Apr 10 17:47:45 joy kernel: [ 5.913798] last sysfs file: /sys/devices/virtual/sound/seq/uevent
Apr 10 17:47:45 joy kernel: [ 5.913832] CPU 0
Apr 10 17:47:45 joy kernel: [ 5.913843] Modules linked in: snd_seq snd_timer btusb iwlcore uvcvideo snd_seq_device mac80211 videodev bluetooth v4l2_compat_ioctl32 snd psmouse cfg80211 intel_ips tpm_tis serio_raw soundcore tpm snd_page_alloc nvram tpm_bios lp parport usb_storage usbhid uas hid i915 drm_kms_helper drm ahci e1000e libahci i2c_algo_bit video
Apr 10 17:47:45 joy kernel: [ 5.914037]
Apr 10 17:47:45 joy kernel: [ 5.914048] Pid: 289, comm: plymouthd Not tainted 2.6.38-8-generic #41-Ubuntu LENOVO 3249CTO/3249CTO
Apr 10 17:47:45 joy kernel: [ 5.914087] RIP: 0010:[<ffffffffa00fb4db>] [<ffffffffa00fb4db>] intel_dp_link_down+0x32b/0x400 [i915]
Apr 10 17:47:45 joy kernel: [ 5.914129] RSP: 0018:ffff88022d753748 EFLAGS: 00010286
Apr 10 17:47:45 joy kernel: [ 5.914148] RAX: 0000000000000000 RBX: ffff88022d68f800 RCX: 00000000c0000100
Apr 10 17:47:45 joy kernel: [ 5.914173] RDX: ffff88022eb6a000 RSI: 0000000000000282 RDI: ffff88022e4cb000
Apr 10 17:47:45 joy kernel: [ 5.914199] RBP: ffff88022d753798 R08: ffff88022d752000 R09: 0000000000000000
Apr 10 17:47:45 joy kernel: [ 5.914224] R10: 0000000000000000 R11: 0000000000000000 R12: ffff88022e4cb440
Apr 10 17:47:45 joy kernel: [ 5.914251] R13: 00000000829c0008 R14: ffffc90012064200 R15: 00000000829c0008
Apr 10 17:47:45 joy kernel: [ 5.914275] FS: 00007f6a366db720(0000) GS:ffff8800bb000000(0000) knlGS:0000000000000000
Apr 10 17:47:45 joy kernel: [ 5.914303] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
Apr 10 17:47:45 joy kernel: [ 5.914322] CR2: 0000000000000230 CR3: 000000022e2e0000 CR4: 00000000000006f0
Apr 10 17:47:45 joy kernel: [ 5.914347] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
Apr 10 17:47:45 joy kernel: [ 5.914370] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Apr 10 17:47:45 joy kernel: [ 5.914395] Process plymouthd (pid: 289, threadinfo ffff88022d752000, task ffff88022dd9db80)
Apr 10 17:47:45 joy kernel: [ 5.914422] Stack:
Apr 10 17:47:45 joy kernel: [ 5.914430] ffff88022e4cb3e8 0000000000000000 ffff88022e4cb000 ffff88022eb6a000
Apr 10 17:47:45 joy kernel: [ 5.914458] 0000000000000002 ffff88022d68f800 ffff88022e4cb440 00000000000e4200
Apr 10 17:47:45 joy kernel: [ 5.914485] 00000000f09c000c ffff88022e4cb000 ffff88022d7537e8 ffffffffa00fbbc2
Apr 10 17:47:45 joy kernel: [ 5.914512] Call Trace:
Apr 10 17:47:45 joy kernel: [ 5.914530] [<ffffffffa00fbbc2>] intel_dp_dpms+0x62/0x150 [i915]
Apr 10 17:47:45 joy kernel: [ 5.914554] [<ffffffffa00b574a>] drm_crtc_helper_set_mode+0x4ca/0x4e0 [drm_kms_helper]
Apr 10 17:47:45 joy kernel: [ 5.914584] [<ffffffffa00b647d>] drm_crtc_helper_set_config+0x84d/0xa10 [drm_kms_helper]
Apr 10 17:47:45 joy kernel: [ 5.914614] [<ffffffffa00b4a49>] drm_fb_helper_force_kernel_mode+0x79/0xb0 [drm_kms_helper]
Apr 10 17:47:45 joy kernel: [ 5.914644] [<ffffffffa00b4a8e>] drm_fb_helper_restore+0xe/0x30 [drm_kms_helper]
Apr 10 17:47:45 joy kernel: [ 5.914673] [<ffffffffa00c3eaa>] i915_driver_lastclose+0x3a/0x80 [i915]
Apr 10 17:47:45 joy kernel: [ 5.914703] [<ffffffffa004f6e9>] drm_lastclose+0x49/0x310 [drm]
Apr 10 17:47:45 joy kernel: [ 5.914727] [<ffffffffa0050264>] drm_release+0x314/0x3e0 [drm]
Apr 10 17:47:45 joy kernel: [ 5.914750] [<ffffffff811661ae>] __fput+0xbe/0x200
Apr 10 17:47:45 joy kernel: [ 5.914767] [<ffffffff81166315>] fput+0x25/0x30
Apr 10 17:47:45 joy kernel: [ 5.914788] [<ffffffff81162bf0>] filp_close+0x60/0x90
Apr 10 17:47:45 joy kernel: [ 5.914814] [<ffffffff81069e38>] put_files_struct+0x88/0xf0
Apr 10 17:47:45 joy kernel: [ 5.914834] [<ffffffff81069f64>] exit_files+0x54/0x70
Apr 10 17:47:45 joy kernel: [ 5.914853] [<ffffffff8106a455>] do_exit+0x175/0x410
Apr 10 17:47:45 joy kernel: [ 5.914872] [<ffffffff8106a8a8>] do_group_exit+0x58/0xd0
Apr 10 17:47:45 joy kernel: [ 5.914893] [<ffffffff8107aba7>] get_signal_to_deliver+0x247/0x410
Apr 10 17:47:45 joy kernel: [ 5.914916] [<ffffffff8100b936>] do_signal+0x56/0x180
Apr 10 17:47:45 joy kernel: [ 5.914934] [<ffffffff8107bda5>] ? sys_rt_sigaction+0x95/0xe0
Apr 10 17:47:45 joy kernel: [ 5.914955] [<ffffffff8100bd06>] ? sys_rt_sigreturn+0x106/0x140
Apr 10 17:47:45 joy kernel: [ 5.914977] [<ffffffff8100bae5>] do_notify_resume+0x65/0x80
Apr 10 17:47:45 joy kernel: [ 5.916268] [<ffffffff8100c2d0>] int_signal+0x12/0x17
Apr 10 17:47:45 joy kernel: [ 5.917559] Code: e5 ff ff ff bf 44 8b 73 60 45 89 ef 48 89 45 b8 0f 1f 44 00 00 48 8b 55 c8 45 89 f6 4c 03 72 18 45 89 2e 48 8b 45 b8 48 8b 7d c0 <8b> b0 30 02 00 00 e8 3a fc fe ff e9 75 fe ff ff 81 65 b8 ff bf
Apr 10 17:47:45 joy kernel: [ 5.920321] RIP [<ffffffffa00fb4db>] intel_dp_link_down+0x32b/0x400 [i915]
Apr 10 17:47:45 joy kernel: [ 5.921711] RSP <ffff88022d753748>
Apr 10 17:47:45 joy kernel: [ 5.923072] CR2: 0000000000000230