[Bug 1819728] Please test proposed package

[Łukasz Zemczak]

Hello Michael, or anyone else affected,

Accepted systemd into xenial-proposed. The package will build now and be
available at
https://launchpad.net/ubuntu/+source/systemd/229-4ubuntu21.19 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 and change the tag from
verification-needed-xenial to verification-done-xenial. If it does not
fix the bug for you, please add a comment stating that, and change the
tag to verification-failed-xenial. 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.

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https://bugs.launchpad.net/bugs/1819728

Title:
  Please backport "fix race between daemon-reload and other commands
  #8803" to 16.04 (for UC16) and 18.04 (for UC18)

Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Xenial:
  Fix Committed
Status in systemd source package in Bionic:
  Fix Committed

Bug description:
  [Impact]
  On Ubuntu Core we recently hit the a race in daemon-reload and systemctl twice. This race is fixed in systemd upstream: "fix race between daemon-reload and other commands #8803" and a subsequent fix in "PR#11121".

  Note that this is a general problem in systemd with daemon-reload and
  systemctl commands, we just happen to hit it more often on Ubuntu Core
  but the test-case below explodes just fine on a normal Ubuntu release
  like 16.04 or 18.04 (not on 18.10+ as its fixed there).

  [TEST CASE]
  To reproduce its enough to run:

  for i in $(seq 50); do
    systemctl daemon-reload &
    systemctl start ssh &
  done

  This will result in "systemctl start ssh" hanging in ppoll. With the
  patch applied the hangs go away.

  [REGRESSION POTENTIAL]
  Medium/High, this change is already in the systemd upstream and in use disco and later but the backport required some manual resolving of conflicts the code because changed between 229,237 and the fixed code in 240. Its also
  not fully clear if the fix relies on the new systemd "coldplug" functionality that was added in more recent git revisions.

  The upstream fix is https://github.com/systemd/systemd/pull/8803 and
  https://github.com/systemd/systemd/pull/11121

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