Created attachment 707891 [details]
/etc/systemd/system/autofs.service with SIGUSR2

This is for autofs-5.0.9-12.1.x86_64 on OpenSuSE "Leap" 42.1.
Cause it to mount something, by e.g. "ls /net/remotehost/home/".  For a
test that's more difficult to pass, make the mountpoint busy by e.g.
(cd /net/remotehost/home; sleep 3600 )& .  Now do "systemctl stop autofs"
or reboot the machine.  Autofs receives SIGTERM but does not exit. 
The man page says "that's not a bug, that's a feature".  Eventually
systemd times out and sends (I assume) SIGKILL.  

We need to send at least SIGUSR1 to immediately unmount all automounted
objects that aren't busy, or SIGUSR2 to do a lazy unmount even if they
are busy.  Then autofs will exit on getting SIGTERM and the reboot
finishes at a normal pace.  

I've attached a unit file which fixes the problem for me.