Description of problem:
When we enter rate-limited state we completely disregard /proc/self/mountinfo notifications for some time. If during that time, some mount unit is active (mounted) and the unit gets unmounted manually systemd will still track its state as active (mounted). Subsequent Start() operation on such unit will be effectively NOP. After leaving rate-limited state we will have inconsistency. Mount is unmounted, but systemd will still considered unit as active (mounted).


Version-Release number of selected component (if applicable):
systemd-239-54.el8.x86_64

How reproducible:
deterministic

Steps to Reproduce:
echo 'tmpfs /mnt tmpfs defaults,nofail 0 0' >> /etc/fstab
systemctl daemon-reload 
mkdir -p foo
systemctl start mnt.mount
for ((i=0;i<50;++i)); do mount --bind foo foo; umount foo; done;
umount /mnt; systemctl start mnt.mount; echo $?; mountpoint /mnt; systemctl status mnt.mount; mountpoint /mnt

Actual results:
0
/mnt is not a mountpoint
● mnt.mount - /mnt
   Loaded: loaded (/etc/fstab; generated)
   Active: active (mounted) since Mon 2022-01-03 05:22:08 EST; 54min ago
    Where: /mnt
     What: tmpfs
     Docs: man:fstab(5)
           man:systemd-fstab-generator(8)
    Tasks: 0 (limit: 11356)
   Memory: 4.0K
   CGroup: /system.slice/mnt.mount

Jan 03 05:22:08 ci-vm-10-0-136-183.hosted.upshift.rdu2.redhat.com systemd[1]: mnt.mount: Directory /mnt to mount over is not empty, mounting anyway.
Jan 03 05:22:08 ci-vm-10-0-136-183.hosted.upshift.rdu2.redhat.com systemd[1]: Mounting /mnt...
Jan 03 05:22:08 ci-vm-10-0-136-183.hosted.upshift.rdu2.redhat.com systemd[1]: Mounted /mnt.
/mnt is not a mountpoint

Expected results:
/mnt is mounted as a result of systemctl start mnt.mount.

Additional info:
https://github.com/systemd/systemd/issues/20329