Description of problem:

We need to backport commit d06e8fbce35c2b52ee1d09af4888876d5f2d7ae4 related to user-runtime-dir@.service.
This commit makes sure the user-runtime-dir@.service is really done before starting "systemd --user", which is really required or else race conditions happen leading the "systemd --user" failure.


Version-Release number of selected component (if applicable):

systemd-239-41.el8_3.1.x86_64


How reproducible:

Always using a systemtap script

Steps to Reproduce:

1. Create delay_mount_runtimepath.stp that will delay the mount of /run/user/<UID> operation (here below UID 101166)

  -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
  probe syscall.mount.call {
  	if (argstr =~ "\"/run/user/101166\"") {
  		delay = 1500 + randint(150)
  		printf("PID %lu (%s) entered '%s(%s)', delaying call by %ld\n", pid(), execname(), name, argstr, delay)
  		mdelay(delay)
  	}
  }
  -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

2. Execute the stap script (requires Guru mode)

  -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
  # yum -y install systemtap
  # stap-prep
  # stap -g -v ./delay_mount_runtimepath.stp 
  [...]
  Pass 5: starting run.
  -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

3. Log in through ssh as the target user

  -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
  # ssh rmetrich@localhost true
  -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------


Actual results:

- Stap output:

  -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
  PID 4281 (systemd-user-ru) entered 'mount("tmpfs", "/run/user/101166", "tmpfs", MS_NOSUID|MS_NODEV, "mode=0700,uid=101166,gid=101166,size=190722048")', delaying call by 1575
  -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

- Journal:

  -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
  Apr 06 08:57:17.748899 vm-sssd8 systemd[3994]: pam_unix(systemd-user:session): session opened for user rmetrich by (uid=0)
  Apr 06 08:57:19.284443 vm-sssd8 systemd[3994]: Failed to fully start up daemon: Permission denied
  Apr 06 08:57:19.285148 vm-sssd8 systemd[3995]: pam_unix(systemd-user:session): session closed for user rmetrich
  Apr 06 08:57:19.285853 vm-sssd8 systemd[1]: user: Failed with result 'protocol'.
  Apr 06 08:57:19.286015 vm-sssd8 systemd[1]: Failed to start User Manager for UID 101166.
  Apr 06 08:57:19.286443 vm-sssd8 systemd[1]: Stopping /run/user/101166 mount wrapper...
  Apr 06 08:57:19.287687 vm-sssd8 sshd[3991]: pam_systemd(sshd:session): Failed to create session: Start job for unit user failed with 'failed'
  -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

Expected results:

  No error spawning "systemd --user"

Additional info:

  See also BZ #1945569 for hardening this.