dx-packages team mailing list archive

[James Hunt <1357252@xxxxxxxxxxxxxxxxxx>]

>From @teds findings:

"The Upstart job creates the cgroup as it goes through each phase in the
job, but it sets the cgroup to be destroyed when all of its PIDs are
gone. When starting the second or later task (what ever that might be,
seems to be post-stop a lot though) there is then a race between
starting that task and the cgroup being destroyed if all of the PIDs in
the group have exited with the main job. On entering the function to
create the task the group is created, and if right then cgmanager
realizes the PIDs are gone it deletes it before the new PID can be
added."

The solution is to not mark created cgroups 'remove-on-empty'
immediately after they are created, but instead to request cgmanager
mops up the cgroups after the last job processes cgroups have been
created.

Note that this approach works correctly for system jobs which specify
the cgroup stanza. However, it is not currently reliable for session
jobs since because logind does not clean up cgroups itself, systemd-shim
arranges for this to happen on behalf of the users session by marking
the logind-created cgroups 'remove-on-empty' and letting cgmanager clean
up.... which brings us back to the problem which the upstart changes are
designed to fix.

So, further works is required to resolve this problem by enhancing
systemd-shim to implement 'abandoncgroup' and 'stopsession' so that
logind works as expected.

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https://bugs.launchpad.net/bugs/1357252

Title:
  upstart can race with cgmanager when using remove-on-empty

Status in Ubuntu Application Launcher:
  Invalid
Status in Upstart:
  In Progress
Status in “cgmanager” package in Ubuntu:
  Fix Released
Status in “systemd-shim” package in Ubuntu:
  Invalid

Bug description:
  After the ubuntu-app-launch landing in #188
  (http://people.canonical.com/~ogra/touch-image-stats/188.changes), UI
  Toolkit autopilot tests have started failing, see
  http://ci.ubuntu.com/smokeng/utopic/touch/mako/190:20140815:20140811.1/9676/ubuntuuitoolkit/
  and the #188 results too. It's different tests each time, but a bit
  above 10 of them tend to fail on each full run.

  Reproducable locally, where I got 11 such failures.

  To reproduce:
  [terminal 1]
  1. flash/update device if needed
  2. adb shell
  3. apt install ubuntu-ui-toolkit-autopilot
  4. powerd-cli display on bright # leave running, also unlock the screen so that lenses are shown
  [terminal 2]
  5. phablet-config autopilot --dbus-probe enable # wait until finishes
  6. phablet-test-run ubuntuuitoolkit

  A full test suite run will take around 0.5h and should produce a bunch
  of 'Application failed to start.':s.

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