Description of problem:

Even while the user is still on the host with logged-in status, the user@.service can be stopped with systemctl stop user manually. There are some situations that user is not running but the user is still on the host.

A customer had a expectation that the systemd-logind should start the user if it's not running, even if the user is available with logged-in status.

Currently, it's checked in user_start() as below.

int user_start(User *u) {
        assert(u);

        if (u->started && !u->stopping)
                return 0;
... snip ...

        /* Start user */
        user_start_service(u);

So, the user is checked, but the status of user is not checked.

Version-Release number of selected component (if applicable):
Red Hat Enterprise Linux 8.7

How reproducible:
Always

Steps to Reproduce:
1. login with a test user (UID=1000)
2. confirm if user is running, and stop it.
3. login with the same test user (UID=1000) to make another session.
4. check if user is running or if systemd -user is running for UID=1000

Actual results:
The systemd-logind doesn't start user when the user is available.

Expected results:
The systemd-logind can start user if it's not activated, even when the user is available.