20.04.1 hang/shutdown failure when changing SSID

[Rafael David Tinoco]

> A series of messages like this one (but for a number of different
> processes) appear on the console log:-
> 
> Aug 13 08:40:54 t470 kernel: [166747.511815] INFO: task NetworkManager:529 blocked for more than 120 seconds.
> Aug 13 08:40:54 t470 kernel: [166747.511855]       Tainted: G W         5.4.0-42-generic ✔ 6-Ubuntu
> Aug 13 08:40:54 t470 kernel: [166747.511886] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> Aug 13 08:40:54 t470 kernel: [166747.511921] NetworkManager  D    0 529      1 0x00000000
> 

You should file a bug in:

https://bugs.launchpad.net/ubuntu/+source/linux/

And provide a kernel dump. A hang like this usually means that kernel is
locked at some entry point for the wireless driver.

You can follow:

https://ubuntu.com/server/docs/kernel-crash-dump

Idea is that you panic the machine by hand, with kdump-tools installed
and enabled, so it can generate the dump into /var/crash for someone to
analyze.

-rafaeldtinoco