Description of problem:

When restarting a mount unit using "systemctl restart <mountpoint>.mount" command, the system enters Emergency target due to failure of local-fs.target.
The issue happens when having some unrelated mount point having a symlink component in its path, as shown in the example below:
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
# ls -l /mnt
total 0
drwxr-xr-x. 2 root root 6 Aug 30 11:52 mountpoint
drwxr-xr-x. 2 root root 6 Aug 30 11:52 othermountpoint
lrwxrwxrwx. 1 root root 1 Aug 30 11:58 symlinktoself -> .

# tail -2 /etc/fstab
/root/test_fs1       /mnt/symlinktoself/mountpoint    xfs     defaults  0 0
/root/test_fs2       /mnt/othermountpoint      xfs     defaults  0 0
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

Here above, /etc/fstab uses a symlink component in first mount "/mnt/symlinktoself/mountpoint". The real path is "/mnt/mountpoint" but that path is not used on purpose.

When restarting mnt-othermountpoint.mount unit, system enters Emergency target.

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

systemd-219-78.el7_9.7.x86_64

How reproducible:

Always

Steps to Reproduce:
1. Create the above setup

  -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
  # truncate -s1G /root/test_fs1 && mkfs.xfs /root/test_fs1
  # truncate -s1G /root/test_fs2 && mkfs.xfs /root/test_fs2
  # cat >> /etc/fstab << EOF
  /root/test_fs1       /mnt/symlinktoself/mountpoint    xfs     defaults  0 0
  /root/test_fs2       /mnt/othermountpoint      xfs     defaults  0 0
  EOF

  # mkdir /mnt/othermountpoint /mnt/mountpoint
  # ln -s . /mnt/symlinktoself
  -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

2. Reboot the system and confirm mounts are up

  -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
  # mount | grep test_
  /root/test_fs1 on /mnt/mountpoint type xfs (rw,relatime,seclabel,attr2,inode64,noquota)
  /root/test_fs2 on /mnt/othermountpoint type xfs (rw,relatime,seclabel,attr2,inode64,noquota)
  -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

3. Restart mnt-othermountpoint.mount unit

  -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
  # systemctl restart mnt-othermountpoint.mount unit
  -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

Actual results:

Emergency target being entered due to "mnt-symlinktoself-mountpoint.mount" failing because it's already mounted.

Expected results:

No issue

Additional info:

Digging into this, it appears the issue happens because of systemd not considering "mnt-symlinktoself-mountpoint.mount" and "mnt-mountpoint.mount" units being the same. systemd indeed sees 2 different units:

1. the "real" mount, based on /proc/self/mountinfo view, which is some "transient mount"

  -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
  # systemctl status mnt-mountpoint.mount 
  ● mnt-mountpoint.mount - /mnt/mountpoint
     Loaded: loaded (/proc/self/mountinfo)
     Active: active (mounted) since Wed 2023-08-30 12:02:34 CEST; 51min ago
      Where: /mnt/mountpoint
       What: /dev/loop0
  
  Aug 30 12:02:34 vm-systemd7 systemd[1]: mnt-mountpoint.mount changed dead -> mounted

  # systemctl cat mnt-mountpoint.mount
  No files found for mnt-mountpoint.mount.
  -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

2. the "static" mount (generated by fstab-generator), which got mounted at boot but is now considered as unmounted

  -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
  # systemctl status mnt-symlinktoself-mountpoint.mount 
  ● mnt-symlinktoself-mountpoint.mount - /mnt/symlinktoself/mountpoint
     Loaded: loaded (/etc/fstab; bad; vendor preset: disabled)
     Active: inactive (dead) since Wed 2023-08-30 12:02:34 CEST; 52min ago
      Where: /mnt/symlinktoself/mountpoint
       What: /root/test_fs1
       Docs: man:fstab(5)
             man:systemd-fstab-generator(8)
    Process: 575 ExecMount=/bin/mount /root/test_fs1 /mnt/symlinktoself/mountpoint -t xfs (code=exited, status=0/SUCCESS)
  
  Aug 30 12:02:34 vm-systemd7 systemd[1]: mnt-symlinktoself-mountpoint.mount changed dead -> mounting
  Aug 30 12:02:34 vm-systemd7 systemd[1]: Mounting /mnt/symlinktoself/mountpoint...
  Aug 30 12:02:34 vm-systemd7 systemd[575]: Executing: /bin/mount /root/test_fs1 /mnt/symlinktoself/mountpoint -t xfs
  Aug 30 12:02:34 vm-systemd7 systemd[1]: Child 575 belongs to mnt-symlinktoself-mountpoint.mount
  Aug 30 12:02:34 vm-systemd7 systemd[1]: Unwatching 575.
  Aug 30 12:02:34 vm-systemd7 systemd[1]: mnt-symlinktoself-mountpoint.mount mount process exited, code=exited status=0
  Aug 30 12:02:34 vm-systemd7 systemd[1]: mnt-symlinktoself-mountpoint.mount changed mounting -> mounted
  Aug 30 12:02:34 vm-systemd7 systemd[1]: Job mnt-symlinktoself-mountpoint.mount/start finished, result=done
  Aug 30 12:02:34 vm-systemd7 systemd[1]: Mounted /mnt/symlinktoself/mountpoint.
  Aug 30 12:02:34 vm-systemd7 systemd[1]: mnt-symlinktoself-mountpoint.mount changed mounted -> dead
  
  # systemctl cat mnt-symlinktoself-mountpoint.mount
  # /run/systemd/generator/mnt-symlinktoself-mountpoint.mount
  # Automatically generated by systemd-fstab-generator
  
  [Unit]
  SourcePath=/etc/fstab
  Documentation=man:fstab(5) man:systemd-fstab-generator(8)
  Before=local-fs.target
  
  [Mount]
  What=/root/test_fs1
  Where=/mnt/symlinktoself/mountpoint
  Type=xfs
  -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

Due to this, when remounting some unrelated mount, systemd enqueues "local-fs.target/restart" job, which makes it realize "mnt-symlinktoself-mountpoint.mount" is not mounted, causing a mount to be done, which fails in "already mounted" because the mount is actually "mnt-mountpoint.mount".

The issue may apparently also happen during a "daemon-reload" but I wasn't able to trigger it.