on WSL systemd status fails output

[Jean-Baptiste Lallement]

[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@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: /

[Jean-Baptiste Lallement (jibel)]

upstream patch

[Jean-Baptiste Lallement (jibel)]

debdiff with patch applied

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "8e57759d6d80ef772d8e17a4559a6797e09af93a.patch" seems to be a patch. If it isn't, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are a member of the ~ubuntu-reviewers, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issues please contact him.]

[Nick Rosbrook (enr0n)]

The fix for this is included in v256, which is currently in oracular-proposed. So we just need to upload the fix to noble.

[Nick Rosbrook (enr0n)]

@jibel - thanks for the patch. I already had it prepped in git, so I will upload that version.

[Timo Aaltonen (tjaalton)]

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.

[Jean-Baptiste Lallement (jibel)]

I've been able to reproduce the problem on Ubuntu WSL 24.04 with systemd 255.4-1ubuntu8.1.
I verified that version 255.4-1ubuntu8.2 fixes it.

u@drenec:~$ systemctl status
● drenec
    State: running
    Units: 359 loaded (incl. loaded aliases)
     Jobs: 0 queued
   Failed: 0 units
    Since: Mon 2024-07-08 09:41:07 CEST; 1h 1min ago
  systemd: 255.4-1ubuntu8.2
  Tainted: cgroupsv1
   CGroup: /
           ├─init.scope
           │ ├─ 1 /sbin/init
           │ ├─ 2 /init
           │ ├─ 6 plan9 --control-socket 6 --log-level 4 --server-fd 7 --pipe-fd 9 --log-truncate
           │ ├─325 /init
           │ ├─326 /init
           │ ├─327 -bash
           │ ├─546 systemctl status
           │ └─547 less

Marking as verification-done.

[Launchpad Janitor (janitor)]

This bug was fixed in the package systemd - 255.4-1ubuntu8.2

---------------
systemd (255.4-1ubuntu8.2) noble; urgency=medium

  * mountpoint-util: Deal with kernel API breakage in "norecovery" mount option.
    Also include fixup commit
    055b465a3f ("shared/mountpoint-util: for old kernels, assume "norecovery" is supported by btrfs").
    (LP: #2067907)
  * cgroup-util: allow cg_read_pid() to skip unmapped (zero) pids (LP: #2067922)
  * debian/extra: ship nice.conf for journald, not logind (LP: #2067927)

 -- Nick Rosbrook <email address hidden> Fri, 14 Jun 2024 17:03:19 -0400

[Łukasz Zemczak (sil2100)]

The verification of the Stable Release Update for systemd has completed successfully and the package is now being released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.