[Bug 1821255] Re: Restart policy "Always" doesn't work under certain circumstances

[Heitor R. Alves de Siqueira]

I've updated the description with a simpler test case that doesn't require an
override file, but this bug can also be verified with the Restart=always directive:

ubuntu at disco:~$ cat /etc/systemd/system/iscsid.service.d/override.conf
[Service]
Restart=always

ubuntu at disco:~$ sudo pkill iscsid

ubuntu at disco:~$ sudo systemctl status iscsid
● iscsid.service - iSCSI initiator daemon (iscsid)
   Loaded: loaded (/lib/systemd/system/iscsid.service; disabled; vendor pre
  Drop-In: /etc/systemd/system/iscsid.service.d
           └─override.conf
   Active: inactive (dead)
     Docs: man:iscsid(8)


** Tags added: sts

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Title:
  Restart policy "Always" doesn't work under certain circumstances

Status in open-iscsi package in Ubuntu:
  Confirmed
Status in open-iscsi source package in Bionic:
  Confirmed
Status in open-iscsi source package in Cosmic:
  Confirmed
Status in open-iscsi source package in Disco:
  Confirmed

Bug description:
  [Impact]
  iscsid restart fails when killed with SIGTERM

  [Description]
  If systemd tries to execute a command that talks to iscsid via iscsid.socket, it can hang if iscsid is not running (or is in the process of being stopped). This can happen due to the current ExecStop= directive, which calls iscsiadm to kill iscsid, and prevents the service from being restarted even when we set Restart=always in the iscsid unit file.

  The solution is to let systemd terminate iscsid by itself. The default action
  when omitting the ExecStop directive is to send SIGTERM to the process group,
  which is equivalent to invoking "iscsiadm -k" (the current ExecStop command).

  [Test Case]
  1) Deploy a Disco VM e.g. with uvt-kvm
      $ uvt-kvm create disco release=disco

  2) Run the deploy-tgt.sh script in the VM to setup an iSCSI target in the
  localhost. The script will install tgt and open-iscsi, configure a 1G
  file-backed iSCSI target, login and restart iscsid.service
      ubuntu at disco:~$ ./deploy-tgt.sh

  3) Kill iscsid with SIGTERM
      ubuntu at disco:~$ sudo pkill iscsid

  4) Try to stop iscsid.service and check whether it hangs
      ubuntu at disco:~$ sudo systemctl stop iscsid

  If we remove the ExecStop= directive, it works as expected:
      ubuntu at disco:~$ sudo systemctl stop iscsid
      ubuntu at disco:~$
  This also causes Restart=always to work as expected.

  [Regression Potential]
  This shouldn't introduce any regressions, since iscsiadm -k just sends SIGTERM to iscsid's process group and that's equivalent to the default systemd ExecStop action. Nonetheless, changes will be tested with autopkgtests and different iscsi scenarios.

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