I was also able to reproduce this in kernels 4.4.0-139, -140 and -141. Kernel 4.4.0-138 worked fine. On kernel 4.4.0-140, the freeze didn't occur instantly but after about 20 seconds, so I was able to capture a stacktrace.
-- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1803929 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 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1803929/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : email@example.com Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp