how do i force upperdir overlayfs to reread/reload lowerdir

i am having the following problem with an overlayfs: I can mount an overlayfs fine using the following line in my etc/fstab

none /home/student overlayfs lowerdir=/home/student,upperdir=/home/.student_rw 0 0

this works great and the mount command displays the overlayfs corretly:

 pc:~$ mount -l -t overlayfs
 none on /home/student type overlayfs (rw,lowerdir=/home/student,upperdir=/home/.student_rw)

so now when a student logs out of the machine i delete the contents of /home/.student_rw using a script - which also works fine.

the problem is that the student logging in, should find a clean home directory with the settings preconfigured in (/home/student) as the overlayfs does not touch the lowerdir folder.

the exact same approach worked very well for aufs, which are no longer supported in precise.

interestingly, the overlayfs approach works fine as long as i reboot the machine. so how can i fix this problem? for me a possible solution seems to be to let the upperdir reread the lowerdir. how would i do that?

thanks