Comment # 7 on bug 962866 from Jiri Slaby

Nevermind, the true reason is this:
WARNING: CPU: 0 PID: 1151 at ../include/linux/kref.h:46
drm_framebuffer_reference+0x64/0x70 [drm]()
Modules linked in: ... [last unloaded: vboxdrv]
CPU: 0 PID: 1151 Comm: X Tainted: G        W  O    4.4.0-1-default #1
Hardware name: Hewlett-Packard HP EliteBook 8470p/179B, BIOS 68ICF Ver. F.40
01/31/2013
 ffffffffa01ee7e1 ffff88032ce7baa8 ffffffff8137f639 0000000000000000
 ffff88032ce7bae0 ffffffff8107d132 ffff880036d3af40 ffff8800a19781c0
 ffff8800a19781c0 ffff88030aee4400 ffff88032ef10000 ffff88032ce7baf0
Call Trace:
 [<ffffffff8101a095>] try_stack_unwind+0x175/0x190
 [<ffffffff81018fe9>] dump_trace+0x69/0x3a0
 [<ffffffff8101a0fb>] show_trace_log_lvl+0x4b/0x60
 [<ffffffff8101942c>] show_stack_log_lvl+0x10c/0x180
 [<ffffffff8101a195>] show_stack+0x25/0x50
 [<ffffffff8137f639>] dump_stack+0x4b/0x72
 [<ffffffff8107d132>] warn_slowpath_common+0x82/0xc0
 [<ffffffff8107d22a>] warn_slowpath_null+0x1a/0x20
 [<ffffffffa01c8294>] drm_framebuffer_reference+0x64/0x70 [drm]
 [<ffffffffa01da1bd>] drm_atomic_set_fb_for_plane+0x2d/0x90 [drm]
 [<ffffffffa026db6c>] __drm_atomic_helper_set_config+0xbc/0x3a0
[drm_kms_helper]
 [<ffffffffa026fa9c>] drm_fb_helper_pan_display+0x18c/0x230 [drm_kms_helper]
 [<ffffffffa037eb0a>] intel_fbdev_pan_display+0x1a/0x60 [i915]
 [<ffffffff813f6a6f>] fb_pan_display+0xcf/0x160
 [<ffffffff813f10b0>] bit_update_start+0x20/0x50
 [<ffffffff813ee233>] fbcon_switch+0x3b3/0x600
 [<ffffffff81481668>] redraw_screen+0x178/0x260
 [<ffffffff81477f3f>] complete_change_console+0x3f/0xe0
 [<ffffffff814786ce>] vt_ioctl+0x6ee/0x12c0
 [<ffffffff8146bd61>] tty_ioctl+0x361/0xc30
 [<ffffffff8120e328>] do_vfs_ioctl+0x288/0x470
 [<ffffffff8120e589>] SyS_ioctl+0x79/0x90

BUG: unable to handle kernel NULL pointer dereference at 0000000000000060
IP: [<ffffffffa0375cfc>] intel_fb_obj_invalidate+0x1c/0xf0 [i915]
PGD 32cb59067 PUD 32131c067 PMD 0
Oops: 0000 [#1] PREEMPT SMP
Modules linked in: ...
CPU: 0 PID: 1151 Comm: X Tainted: G        W  O    4.4.0-1-default #1
Hardware name: Hewlett-Packard HP EliteBook 8470p/179B, BIOS 68ICF Ver. F.40
01/31/2013
task: ffff88032c71e240 ti: ffff88032ce78000 task.ti: ffff88032ce78000
RIP: 0010:[<ffffffffa0375cfc>]  [<ffffffffa0375cfc>]
intel_fb_obj_invalidate+0x1c/0xf0 [i915]
RSP: 0018:ffff88032ce7bac8  EFLAGS: 00010246
RAX: ffff88032c71e240 RBX: ffff8802fb63be00 RCX: ffff88012ae9dfc0
RDX: ffff880036d3af40 RSI: 0000000000000000 RDI: ffff8802fb63be00
RBP: ffff88032ce7baf0 R08: ffffea000c3eb7df R09: 0000000000000008
R10: ffff8800aae9db80 R11: ffff8800aae9d780 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000200001 R15: 0000000000000080
FS:  00007f1dfefbca00(0000) GS:ffff88033ea00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000060 CR3: 000000032d524000 CR4: 00000000001406f0
Stack:
 ffff88032f62e600 ffff88032fb35800 0000000000000000 0000000000200001
 0000000000000080 ffff88032ce7bb10 ffffffffa037ebf3 0000000000000000
 ffff88032ce7bc68 ffff88032ce7bc48 ffffffff813f6ed8 ffff88032fb35860
Call Trace:
 [<ffffffffa037ebf3>] intel_fbdev_set_par+0x43/0x60 [i915]
 [<ffffffff813f6ed8>] fb_set_var+0x238/0x460
 [<ffffffff813ed749>] fbcon_blank+0x2e9/0x330
 [<ffffffff81482ac3>] do_unblank_screen+0xc3/0x190
 [<ffffffff81477f59>] complete_change_console+0x59/0xe0
 [<ffffffff814786ce>] vt_ioctl+0x6ee/0x12c0
 [<ffffffff8146bd61>] tty_ioctl+0x361/0xc30
 [<ffffffff8120e328>] do_vfs_ioctl+0x288/0x470
 [<ffffffff8120e589>] SyS_ioctl+0x79/0x90
Code: 41 5f 5d c3 90 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 48 89 e5
41 57 41 56 41 55 41 54 41 89 f5 53 4c 8b 67 08 48 89 fb <41> 8b 44 24 60 4d 8b
74 24 28 83 f8 01 74 58 8b b3 5c 01 00 00
RIP  [<ffffffffa0375cfc>] intel_fb_obj_invalidate+0x1c/0xf0 [i915]
 RSP <ffff88032ce7bac8>
CR2: 0000000000000060