Description of problem:
 With openshift workloads, commands such as the following are issued repeatedly:

    systemd-run --description='Kubernetes transient mount for /var/lib/origin/openshift.local.volumes/pods/<val>/volumes/kubernetes.io~secret/<val>' --scope -- mount -t tmpfs tmpfs /var/lib/origin/openshift.local.volumes/pods/<val>/volumes/kubernetes.io~secret/<val>

When the mount point is within a bind-mounted directory, the behaviour results in a large number of "loaded inactive dead" mount points. Eventually the commands will fail with the following error message visible in the system logs.

    systemd: Failed to set up mount unit: Argument list too long


This issue was reported upstream in the following:

    https://github.com/kubernetes/kubernetes/issues/57345


Which pushed the investigation to an upstream systemd issue documented in:

    https://github.com/systemd/systemd/issues/7798


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

    systemd-219-62.el7_6.2.x86_64


How reproducible:

    Difficult, though the underlying suspected problem is fairly simple

Steps to Reproduce:
1. Create a directory and bind mount it to itself

    # mkdir /mnt/test && mount --bind /mnt/test /mnt/test

2. Mount additional directories under the above

    # mkdir /mnt/test/subdir1 && mount -t tmpfs tmpfs /mnt/test/subdir1

3. Verify the state of the underlying subdir

    # systemctl list-units --type mount --all | grep test


Actual results:

    # systemctl list-units --type mount --all | grep test
    mnt-test-subdir1.mount        loaded inactive dead    /mnt/test/subdir1
    mnt-test.mount                loaded active   mounted /mnt/test


Expected results:

    # systemctl list-units --type mount --all | grep test
    mnt-test-subdir1.mount        loaded active   mounted /mnt/test/subdir1
    mnt-test.mount                loaded active   mounted /mnt/test    


Additional info:

    The cause of the "systemd: Failed to set up mount unit: Argument list too long" error message is suspected to be continued growth of "inactive dead" mount units that cannot be removed and eventual failure in the following codepath:

    src/core/unit.c
    int unit_add_name(Unit *u, const char *text) {
            _cleanup_free_ char *s = NULL, *i = NULL;
            UnitType t;
            int r;
    <snip>
            if (hashmap_size(u->manager->units) >= MANAGER_MAX_NAMES)
                    return -E2BIG;
    <snip>