Comment # 23 on bug 865337 from Joschi Brauchle

We are having the same problem at our institute in combination with NFSv4 and
Kerberos mounts.

The user mounts its home from an NFSv4 server via autofs. Unfortunately, due to
systemd leaving an "(sd-pam)" process hanging around which accesses the user
home even after user logout, the NFSv4 share cannot be unmounted. 

After a while, the user kerberos tickets for the nfsv4 mount expires and things
are in a big mess, as the user is not even aware of the situation as he has
logged out long before. The "(sd-pam)" processes and now inaccessible nfs4
mounts keep sticking around forever until the machine is rebooted.

We currently refrain to automatically kill all "(sd-pam)" processes after user
logout to prevent this scenario. Not nice...