[Pkg-xen-devel] Bug#932759: After upgrade from stretch to buster, removal of obsolete xen 4.8 packages seems to trigger shutdown of xenconsoled

[niek]

Package:  xen-hypervisor-4.11-amd64
Version: 4.11.1+92-g6c33308a8d-2
System: Linux [host] 4.19.0-5-amd64 #1 SMP Debian 4.19.37-5+deb10u1
(2019-07-19) x86_64 GNU/Linux
Debian Release:        10
Codename:       buster

In Reference To: Debian bug #851654 (archived)
> On Mon, 21 Jan 2019 00:48:09 +0100 Hans van Kranenburg
> <hans at knorrie.org> wrote:
>> reassign 851654 src:xen
>> thanks
>>
>> Hm!
>>
>> I think this is the same one that I've been observing during upgrade
>> tests from 4.8 -> 4.11 and 4.10 -> 4.11.
>>
>> In my IRC logs I can find myself complaining about xenconsoled that's
>> suddenly gone multiple times during 2018. I didn't manage to track this
>> issue down yet. The IRC logs contain some links to expired pastebin
>> entries. :|
>>
>> Also, in some cases xenconsoled just got shut down during the night,
>> during some systemd reload whatever was happening.
>>
>> I suspect more users are going to run into this issue when upgrading to
>> Buster.
>>
>> Hans

What happened:
- upgraded Debian Xen Dom0 from stretch to buster and rebooted, as
described in
https://www.debian.org/releases/buster/amd64/release-notes/ch-upgrading.en.html

- started some Linux pv domu without problems

- removed obsolete packages with 'apt autoremove'. This removed (among
others)
xen-hypervisor-4.8-amd64:amd64 (4.8.5+shim4.10.2+xsa282-1+deb9u11),
libxen-4.8:amd64 (4.8.5+shim4.10.2+xsa282-1+deb9u11),
xen-utils-4.8:amd64 (4.8.5+shim4.10.2+xsa282-1+deb9u11)

- starting another pv domu the next day using 'xl create -c [domu.cfg]'
raised an error message:
"xenconsole: Could not read tty from store: Success"

- opening a console for an already running domu raised another error
message that I believe was:
"xenconsole: Could not open tty `/dev/pts/2': No such file or directory"

- some internet searching hinted that this could be caused by
xenconsoled not running.

- xenconsoled was not running

- searching system logs revealed that xenconsoled seemed to have stopped
when 'apt autoremove' removed the obsolete xen 4.8
packages after upgrading to xen 4.11.

- this coincided with a systemd reload as seen in journalctl:
Jul 21 07:38:40 host systemd[1]: Reloading.
Jul 21 07:38:40 host systemd[1]: serial-getty at hvc0.service: Current
command vanished from the unit file, execution of the command list won't
be resumed.
Jul 21 07:38:40 host systemd[1]: serial-getty at ttyS1.service: Current
command vanished from the unit file, execution of the command list won't
be resumed.
Jul 21 07:38:40 host systemd[1]: getty at tty1.service: Current command
vanished from the unit file, execution of the command list won't be resumed.
Jul 21 07:38:41 host systemd[1]: Stopping LSB: Xen daemons...
Jul 21 07:38:41 host xen[9092]: Stopping Xen daemons: xenconsoled.
Jul 21 07:38:41 host systemd[1]: xen.service: Succeeded.
Jul 21 07:38:41 host systemd[1]: Stopped LSB: Xen daemons.

Note that at this time domu's where already running under xen4.11.

'systemctl restart xen.service' solved the issue. I report the issue
because it could affect others that are performing upgrades.