hang booting kernel after software reboot

[Gregory Smith]

After issuing a software reboot, the machine hangs at a black screen after the grub prompt, before the kernel boots. This lasts at least five minutes, with the processor fans spun all the way up. If I remove quiet and nosplash there is no text, the screen is completely black.

I have tried various reboot= options but it behaves the same way (when it reboots--some of those options do not reboot at all). If I add acpi=off it will boot reliably, but with acpi=ht the same problem occurs.

Once at the black screen, I can press the reset button, and after going through grub, the machine boots successfully. It also boots successfully on a cold boot.

I am using UEFI, but I had the same problem with BIOS boot.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: linux-image-5.8.0-63-generic 5.8.0-63.71~20.04.1
ProcVersionSignature: Ubuntu 5.8.0-63.71~20.04.1-generic 5.8.18
Uname: Linux 5.8.0-63-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.18
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Thu Jul 22 20:51:41 2021
InstallationDate: Installed on 2021-07-18 (4 days ago)
InstallationMedia: Ubuntu 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
SourcePackage: linux-signed-hwe-5.8
UpgradeStatus: No upgrade log present (probably fresh install)