Comment 8 for bug 1837227

I've now successfully tested this on Bionic, Focal and Jammy. Using a test script based on upstream's bug report, several systemd mount units are created that are tmpfs-backed for better performance. The basic routine of the script is as follows:

- mount the unit (or target mount point)
- sleep 1s
- verify whether the mount exists and is mounted correctly

This is done concurrently with 100 mountpoints, through 40 test loops by default. Additionally, the script covers all variants of this issue that were reported upstream:
1) install all systemd units at once, mount with 'systemctl start' all units
2) install each systemd unit when mounting, mount with 'systemctl start' each unit
3) mount directly with 'systemd-mount'
4) mount directly with 'mount'
5) install each systemd unit when mounting, mount with 'systemctl start',
   trigger multiple 'systemctl daemon-reload' throughout test loop
Each of these scenarios has an equivalent test "variant" in the script that can be invoked directly. Unless specified otherwise, only scenario 4 is tested.

Without the systemd and kernel fixes, at least one of the above scenarios seems to fail consistently in Bionic and Focal. After installing test packages from the PPAs [0] and [1], I've been able to run the test script without any errors for multiple iterations.

[0] https://launchpad.net/~halves/+archive/ubuntu/339757-test-kernel
[1] https://launchpad.net/~halves/+archive/ubuntu/339757-test-systemd