[Bug 1911352] Re: Black screen on boot after 20.04 upgraded to kernel 5.8

Ben, can you tell us if it was 5.8.0-34 kernel or later?

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Title:
Black screen on boot after 20.04 upgraded to kernel 5.8

Status in linux package in Ubuntu:
Incomplete

Bug description:
Yesterday Ubuntu asked me to reboot after automatic updates, and when
I rebooted it doesn't start up. Sometimes it stays on the Dell logo,
sometimes it goes to a black screen and doesn't get past that (not
sure what causes each variation -- perhaps for reboot it does the Dell
logo, cold start up it does the black screen?).

After the updates it's trying to boot the 5.8.0 kernel. In the boot
menu, if I manually select the 5.4.0 kernel everything works fine. So
presumably it's something about the 5.8 kernel on this hardware.

When this occurred I was running the Nouveau open source graphics
driver. I switched to the NVIDIA driver (460) to see if that would
help, but it didn't change anything. So it may or may not be graphics
related.

I'm attaching my /var/log/kern.log and /var/log/syslog for yesterday
-- Jan 12, I think it would be around 13:30 that I first rebooted
after the upgrade (and a bunch of times after that). I ran the logs
through grep -v 'var-snap-lxd-common-lxd' as a huge percentage of the
lines were this (presumably irrelevant):

Jan 12 19:09:55 BenXPS15 kernel: [14515.297170] audit: type=1400
audit(1610431795.003:29126): apparmor="DENIED" operation="open"
namespace="root//lxd-juju-804318-0_<var-snap-lxd-common-lxd>"
profile="snap.juju-db.daemon" name="/proc/631/net/netstat" pid=3906
comm="ftdc" requested_mask="r" denied_mask="r" fsuid=1000000
ouid=1000000

For reference:

* This is a Dell XPS 15 (9550) laptop with an NVIDIA GeForce GTX 960M (I think it's hybrid graphics). i7-6700HQ 2.6GHz with 8 cores, 256 GB SSD, 16 MB RAM.
* I installed Ubuntu 20.04 Focal in August 2020, and now it says it's on "Ubuntu 20.04.1 LTS".
* /proc/version_signature: Ubuntu 5.4.0-59.65-generic 5.4.78
* "sudo lspci -vnvn" output is included in the attached logs.zip

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