[Bug 1803929] Re: Summary: Kernel bug (unhandled paging request) on "udisksctl power-off"

Created Q&A on AskUbuntu ( https://askubuntu.com/q/1099414/66509 ) to
help other users keep their data safe.

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Title:
Summary: Kernel bug (unhandled paging request) on "udisksctl power-
off"

Status in linux package in Ubuntu:
Confirmed

Bug description:
lsb_release -rd
Description: Ubuntu 16.04.5 LTS
Release: 16.04

uname -a
Linux metabox 4.4.0-139-generic #165-Ubuntu SMP Wed Oct 24 10:58:50 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

Steps (1) to reproduce:
1) Plug in a USB3 hard drive.
2) Right click on launcher icon.
3) Select "Safely Remove".

After finding this: https://askubuntu.com/a/532691
...the following steps also reproduce the problem.

Steps (2) to reproduce:
1) Plugin in a USB3 hard drive.
2) udisksctl unmount -b /dev/sdXY
3) udisksctl power-off -b /dev/sdX

System completely locks and becomes unresponsive, such that even the Magic SysRq key combination does nothing.
Most of the time the fans on my laptop go crazy (so the CPU must get stuck in some loop), but once they did not and the system was just locked (without the fans going nuts).

I can't get a textual copy of the kernel bug log (because I have to do a hard reset to regain control of the system and the output doesn't get flushed to disk), but I did manage to get a photo of some of it (please refer to attachment).
---
ApportVersion: 2.20.1-0ubuntu2.18
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/pcmC1D0p: matt 2754 F...m pulseaudio
/dev/snd/controlC1: matt 2754 F.... pulseaudio
/dev/snd/controlC0: matt 2754 F.... pulseaudio
CurrentDesktop: Unity
DistroRelease: Ubuntu 16.04
EcryptfsInUse: Yes
HibernationDevice: RESUME=UUID=f00235c0-ba8a-4403-91b1-64e9d87b76e0
InstallationDate: Installed on 2016-04-23 (940 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
MachineType: Notebook N150SD/N155SD
NonfreeKernelModules: zfs zunicode zcommon znvpair zavl
Package: linux (not installed)
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.4.0-139-generic root=UUID=beb9b9ce-39a7-464a-978c-ac4fb82a5a81 ro quiet splash
ProcVersionSignature: Ubuntu 4.4.0-139.165-generic 4.4.160
RelatedPackageVersions:
linux-restricted-modules-4.4.0-139-generic N/A
linux-backports-modules-4.4.0-139-generic N/A
linux-firmware 1.157.20
Tags: xenial
Uname: Linux 4.4.0-139-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo vboxusers wireshark
_MarkForUpload: True
dmi.bios.date: 03/31/2015
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 1.03.05
dmi.board.asset.tag: Tag 12345
dmi.board.name: N150SD/N155SD
dmi.board.vendor: Notebook
dmi.board.version: Not Applicable
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 9
dmi.chassis.vendor: Notebook
dmi.chassis.version: N/A
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr1.03.05:bd03/31/2015:svnNotebook:pnN150SD/N155SD:pvrNotApplicable:rvnNotebook:rnN150SD/N155SD:rvrNotApplicable:cvnNotebook:ct9:cvrN/A:
dmi.product.name: N150SD/N155SD
dmi.product.version: Not Applicable
dmi.sys.vendor: Notebook

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