Pkg xen devel - Jan 2019 - Bug#851654: Prerm maintainer script unconditionally stops xend/xenconsoled

Package: xen-utils-4.4
Severity: normal

Dear Maintainer,

the xen-utils-4.4 and xen-utils-4.1 prerm maintainer scripts contain the
following code snippet:

    remove|upgrade)
        update-alternatives --remove xen-default /usr/lib/xen-4.4
        if [ -x "/etc/init.d/xen" ]; then
            invoke-rc.d xen stop || exit $?
        fi
    ;;

which, in conjunction with the postinst script triggers a xend and xenconsoled
restart that relies on both maintainer scripts being executed.

We triggered a xen stop by removing obsolete xen-utils-4.1 packages while
already using xen-utils-4.4.

Can you think of a way to implement the restart and stop more robustly in that
the stop and start actions are performed atomically or the service shipped in
the unversioned xen-utils-common is not stopped if it has been started by the
maintainer script of a different (newer) xen-utils-X.Y package?

-- System Information:
Debian Release: 9.0
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'testing'), (1,
'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.8.0-2-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_GB.utf-8, LC_CTYPE=en_GB.utf-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Wolodja Wentland writes ("Bug#851654: Prerm maintainer script
unconditionally stops xend/xenconsoled"):
> We triggered a xen stop by removing obsolete xen-utils-4.1 packages while
already using xen-utils-4.4.
Hi.  In recent versions of Xen, xend is gone.  So that part of the
problem is too.

I think a xenconsoled restart should be harmless, so I think it is
probably right that the maintainer scripts end up stopping the old
xenconsoled and starting a new one, at least unless it's going to be
away for a long time.

Does that make sense ?

Ian.

Hi Ian,

On Tue, Jan 17, 2017 at 10:58 +0000, Ian Jackson wrote:
> Wolodja Wentland writes ("Bug#851654: Prerm maintainer script
unconditionally
> stops xend/xenconsoled"): > We triggered a xen stop by removing
obsolete
> xen-utils-4.1 packages while already using xen-utils-4.4.
> I think a xenconsoled restart should be harmless, so I think it is
> probably right that the maintainer scripts end up stopping the old
> xenconsoled and starting a new one, at least unless it's going to be
> away for a long time.
It makes perfect sense for them to restart xenconsoled during package upgrades
which the combination of prerm and postinst scripts achieves for upgrades of the
same versioned package. Upgrades of xen-utils-4.{1,4,8} will all stop
xenconsoled during the prerm run and start it again in the postinst run of the
upgraded package.

The problem we encountered, however, was that we removed obsolete packages
(xen-utils-4.1) after the postinst script of a newer one (xen-utils-4.4) had
already started xenconsoled. The prerm script of xen-utils-4.1 thereby stopped a
daemon that was started by the postinst script of xen-utils-4.4 and xenconsoled
was no longer running as a result. If the maintainer scripts of these versioned
packages would only deal with 'their' version this would not happen.
--
Wolodja <debian at babilen5.org>

4096R/CAF14EFC
081C B7CD FF04 2BA9 94EA  36B2 8B7F 7D30 CAF1 4EFC
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Processing control commands:
> tags -1 confirmed
Bug #851654 [xen-utils-4.4] Prerm maintainer script unconditionally stops
xend/xenconsoled
Added tag(s) confirmed.

-- 
851654: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=851654
Debian Bug Tracking System
Contact owner at bugs.debian.org with problems

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

Processing commands for control at bugs.debian.org:
> reassign 851654 src:xen
Bug #851654 [xen-utils-4.4] Prerm maintainer script unconditionally stops
xend/xenconsoled
Bug reassigned from package 'xen-utils-4.4' to 'src:xen'.
Ignoring request to alter found versions of bug #851654 to the same values
previously set
Ignoring request to alter fixed versions of bug #851654 to the same values
previously set
> thanks
Stopping processing here.

Please contact me if you need assistance.
-- 
851654: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=851654
Debian Bug Tracking System
Contact owner at bugs.debian.org with problems

Your message dated Fri, 22 Feb 2019 16:37:31 +0000
with message-id <E1gxDpL-000AIU-J3 at fasolo.debian.org>
and subject line Bug#851654: fixed in xen 4.11.1+26-g87f51bf366-2
has caused the Debian Bug report #851654,
regarding Prerm maintainer script unconditionally stops xend/xenconsoled
to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.

(NB: If you are a system administrator and have no idea what this
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-- 
851654: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=851654
Debian Bug Tracking System
Contact owner at bugs.debian.org with problems
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Subject: Prerm maintainer script unconditionally stops xend/xenconsoled
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From: Ian Jackson <ijackson at chiark.greenend.org.uk>
Subject: Bug#851654: fixed in xen 4.11.1+26-g87f51bf366-2
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