[  211.045025]  [<ffffffff9351b7d0>] drm_clflush_pages+0x39/0x6c
[  211.045044]  [<ffffffff935a518a>] udl_gem_get_pages+0x44/0x4c
[  211.045062]  [<ffffffff935a524e>] udl_gem_vmap+0x57/0x81
[  211.045079]  [<ffffffff935a3eb5>] udlfb_create+0xae/0x27e
[  211.045096]  [<ffffffff93518ea0>] drm_fb_helper_initial_config+0x387/0x494
[  211.045115]  [<ffffffff93533528>] ? drm_modeset_unlock+0x43/0x46
[  211.045134]  [<ffffffff935a48a3>] udl_fbdev_init+0x9b/0xa6
[  211.045151]  [<ffffffff935a3b2e>] udl_driver_load+0x3c8/0x454
[  211.045169]  [<ffffffff9352138b>] drm_dev_register+0xb0/0x119
[  211.045187]  [<ffffffff935369c8>] drm_get_usb_dev+0x79/0xda
[  211.045204]  [<ffffffff935a26dc>] udl_usb_probe+0x15/0x17
[  211.045221]  [<ffffffff9361385d>] usb_probe_interface+0x17c/0x21c
[  211.045239]  [<ffffffff935af55a>] driver_probe_device+0xae/0x1fa
[  211.045255]  [<ffffffff935af705>] __device_attach_driver+0x5f/0x66
[  211.045271]  [<ffffffff935af6a6>] ? driver_probe_device+0x1fa/0x1fa
[  211.045290]  [<ffffffff935ad9f4>] bus_for_each_drv+0x87/0xaa
[  211.045306]  [<ffffffff935af828>] __device_attach+0x9d/0x101
[  211.045322]  [<ffffffff935af8b1>] device_initial_probe+0x13/0x15
[  211.045338]  [<ffffffff935aea84>] bus_probe_device+0x33/0x96
[  211.045354]  [<ffffffff935acccf>] device_add+0x32e/0x545
[  211.045370]  [<ffffffff936120cd>] usb_set_configuration+0x624/0x674
[  211.045390]  [<ffffffff9361a6bf>] generic_probe+0x45/0x77
[  211.045405]  [<ffffffff936136ce>] usb_probe_device+0x2d/0x40
[  211.045420]  [<ffffffff935af55a>] driver_probe_device+0xae/0x1fa
[  211.045437]  [<ffffffff935af705>] __device_attach_driver+0x5f/0x66
[  211.045452]  [<ffffffff935af6a6>] ? driver_probe_device+0x1fa/0x1fa
[  211.045470]  [<ffffffff935ad9f4>] bus_for_each_drv+0x87/0xaa
[  211.045485]  [<ffffffff935af828>] __device_attach+0x9d/0x101
[  211.045501]  [<ffffffff935af8b1>] device_initial_probe+0x13/0x15
[  211.045516]  [<ffffffff935aea84>] bus_probe_device+0x33/0x96
[  211.045533]  [<ffffffff935acccf>] device_add+0x32e/0x545
[  211.045551]  [<ffffffff9350842a>] ? add_device_randomness+0xec/0x139
[  211.045570]  [<ffffffff936096cc>] usb_new_device+0x29a/0x3c9
[  211.045587]  [<ffffffff9360bb73>] hub_thread+0xa2e/0xeda
[  211.045607]  [<ffffffff9382290f>] ? __schedule+0x3ec/0x5b5
[  211.045626]  [<ffffffff93295956>] ? finish_wait+0x62/0x62
[  211.045642]  [<ffffffff9360b145>] ? usb_reset_device+0x16a/0x16a
[  211.045662]  [<ffffffff9327b372>] kthread+0x108/0x110
[  211.045679]  [<ffffffff9327b26a>] ? __kthread_parkme+0x67/0x67
[  211.045696]  [<ffffffff9382636c>] ret_from_fork+0x7c/0xb0
[  211.045712]  [<ffffffff9327b26a>] ? __kthread_parkme+0x67/0x67
[  211.045726] Code: 00 00 48 b8 00 00 00 00 00 16 00 00 48 b9 00 00 00 00 00 88 ff ff 48 01 c7 48 c1 ff 06 48 c1 e7 0c 48 01 f9 31 ff 89 f8 4
[  211.045897] RIP  [<ffffffff9351b717>] drm_clflush_page+0x46/0x66
[  211.045914]  RSP <ffff88046806f6f8>

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/kernel/+/7b031375cd6d2fff74ae9583e56bd512a3a47f08

commit 7b031375cd6d2fff74ae9583e56bd512a3a47f08
Author: Gurchetan Singh <gurchetansingh@chromium.org>
Date: Wed Dec 14 21:59:54 2016

CHROMIUM: drm/udl: Fix incorrect flush size

We were flushing a 'page_count' number of pages. The
problem is 'page_count' is never defined in the function
and uninitialized. I am surprised this code ever compiled.
Let's fix it.

BUG= chromium:674289 
TEST=try-bots

Change-Id: Idc9252d9d198b0f23b8cb252244789dfeb7657fb
Reviewed-on: https://chromium-review.googlesource.com/419694
Commit-Ready: Gurchetan Singh <gurchetansingh@chromium.org>
Tested-by: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>

[modify] https://crrev.com/7b031375cd6d2fff74ae9583e56bd512a3a47f08/drivers/gpu/drm/udl/udl_gem.c

Verified in Chrome OS 9765.13.0, 61.0.3163.20.