[Bug 2067922] Re: on WSL systemd status fails output

[Timo Aaltonen]

Hello Jean-Baptiste, or anyone else affected,

Accepted systemd into noble-proposed. The package will build now and be
available at
https://launchpad.net/ubuntu/+source/systemd/255.4-1ubuntu8.2 in a few
hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, what testing has been
performed on the package and change the tag from verification-needed-
noble to verification-done-noble. If it does not fix the bug for you,
please add a comment stating that, and change the tag to verification-
failed-noble. In either case, without details of your testing we will
not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

** Changed in: systemd (Ubuntu Noble)
       Status: Triaged => Fix Committed

** Tags added: verification-needed verification-needed-noble

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https://bugs.launchpad.net/bugs/2067922

Title:
  on WSL systemd status fails output

Status in systemd package in Ubuntu:
  Fix Committed
Status in systemd source package in Noble:
  Fix Committed

Bug description:
  [Impact]

  WSL 24.04 / systemd 255.4-1ubuntu8

  * Upstream report: https://github.com/microsoft/WSL/issues/8879
  * Upstream PR: https://github.com/systemd/systemd/pull/32534
  * Upstream commit: https://github.com/systemd/systemd-stable/commit/8e57759d6d80ef772d8e17a4559a6797e09af93a.patch

  In WSL, the cgroup.procs PID list for some reason contain a ton of zeros everywhere from unmapped PIDs.
  Whenever cg_read_pid encounters such a zero, it throws an error. This makes systemd near unusable inside of WSL.

  [Test Plan]

  On WSL running Ubuntu 24.04, run systemctl status. On an affected
  system, there will be an error saying "Failed to dump process list
  [...]". On a patched system, the command should work as expected.

  [Where problems could occur]

  This patch adds a flags parameter to cg_read_pid(), and adds a new
  flag, CGROUP_DONT_SKIP_UNMAPPED. The new default behavior of
  cg_read_pid() is that unmapped pids *will* be skipped. When this flag
  is set in a call to cg_read_pid(), encountering an unmapped pid will
  leave the caller to deal with it.

  There are several places where cg_read_pid() is called in systemd, so
  there are several places where this would come up. If we did see
  problems, it would likely because a caller is skipping the unmapped
  pids when it should not be. For callers that do not skip (i.e. pass
  CGROUP_DONT_SKIP_UNMAPPED), they either handle it cleanly, or
  propagate a different error to signal this case.

  [Original Description]

  WSL 24.04 / systemd 255.4-1ubuntu8

  * Upstream report: https://github.com/microsoft/WSL/issues/8879
  * Upstream PR: https://github.com/systemd/systemd/pull/32534
  * Upstream commit: https://github.com/systemd/systemd-stable/commit/8e57759d6d80ef772d8e17a4559a6797e09af93a.patch

  In WSL, the cgroup.procs PID list for some reason contain a ton of zeros everywhere from unmapped PIDs.
  Whenever cg_read_pid encounters such a zero, it throws an error. This makes systemd near unusable inside of WSL.

  # Test Case
  install Ubuntu WSL 24.04 from the MS STore. This version has systemd already enabled.

  ## Expected Behavior
  systemctl status command to work

  ## Actual Behavior
  toor at XPS:~$ systemctl status
  Failed to dump process list for 'XPS', ignoring: Input/output error
  ● XPS
      State: degraded
      Units: 318 loaded (incl. loaded aliases)
       Jobs: 0 queued
     Failed: 1 units
      Since: Sat 2022-09-24 08:43:15 PDT; 14min ago
    systemd: 251.4-1ubuntu6
    Tainted: cgroupsv1
     CGroup: /

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