Since February this year I have been battling to get kernel 5.0.x to run on my bleeding edge kit, all to no avail. My machine would hang on both reboot and shutdown, requiring a hard, cold boot.
I tried everything under the sun, from every power management kernel option, e.g.
acpi=force, and more. I've installed in CSM mode and reinstalled in UEFI mode, ripped out hardware, updated firmware, started with BIOS defaults, booted with and without fast boot, tried every nVidia driver under the sun, blacklisted hardware all over the place, trawled through kernel release notes until I was almost blind, and regularly covered myself in sackcloth and ashes and gnashed my teeth to stubs. Fortunately I'm quite bald so I don't have any head hair to rip out, though my once once hairy chest is now a patchwork quilt of almost total deforestation.
I distro-hopped left, right and centre. Only Manjaro would run on kernel 5. Not a single Ubuntu based distro would allow me to reboot or shutdown. I contemplated staying with Manjaro but it has some very rough edges that turned me off it, so I kept searching for a solution. The frustration experienced was quite intense. I caught myself at least twice in the last six months contemplating using Windwoes because I absolutely must have working gear.
Early last week, my backup server chucked a wobbly. Its 12TB hardware RAID 5EE set threw out a drive. I keep brand new spare drives around so I pulled out the dicky drive, checked it thoroughly and concluded it must have been an interstellar cosmic particle that knocked an atom out of orbit in the drive; the drive is only 1 year old and came up perfectly clean. I put the drive back in to the RAID set, the RAID controller manager claimed the set was optimal, no rebuild required. One hour later, the entire RAID set came crashing down. My backup RAID set had died completely.
I replaced the drive with a new one, and added a global hot spare for good measure. For RAID 5EE this is double redundancy because RAID 5EE also incorporates a spare into the RAID set itself. I stared into the face of several days of days of data transfer backing up my 12TB hardware RAID 5EE workstation over a gigabit connection. At this point I decided I'd got so far that it was time to try and install the latest and greatest KDE neon on the server. I went through my well-documented procedures and installed KDE neon based on Ubuntu 18.04.3, knowing it had kernel 5.x. Lo and behold, it would reboot and shutdown without question.
So what gives?
The server has an AMD 2700X CPU, and the workstation has an Intel i9-9900K. I rebooted the workstation and began reading and checking every single setting in its BIOS. There had to be a hardware reason that the AMD would reboot and shutdown with kernel 5.0 but the Intel wouldn't. I looked at the screen, gobsmacked... I was disappointed with myself because whenever I update the machine's BIOS I make it a habit to turn off the CPU C-states. I hadn't done that with the last BIOS update. I promptly turned off every CPU C-state, installed KDE neon with kernel 5.0 and rebooted and shutdown the Intel workstation with complete and utter impunity.
I was happier than a pig wallowing in wet muck.
Since I disable all C-states by default and they're now all disabled, and the machine is now running kernel 5.0, and rebooting and shutting down exactly as it should, I'm not really interested in determining what one or combination of C-states is causing the problem. It's one or more of them ^^^^^ up there.
So, to cut a short story long, for those of you who provide your free time supporting LM, if you ever get frustrated over a newcomer's lack of knowledge or ability to express what the problem is, spare them a thought. Not everyone is gifted with the necessary turn of mind to do what you do. Keep up the great work, LM support community
I've seen a few posts referencing this issue but unfortunately getting wires crossed. The problem was with the Intel CPU. The AMD CPU always ran fine. The c-states and hardware prefetcher had to be disabled on the Intel CPU, not the AMD CPU. It was kernel 5.0.x running fine on the AMD that led me to solve the problem on the Intel.
Anyway, thanks for to all who have read this. It seems to have provided some vital information