[dm-crypt] Question about "Add scsi_debug_teardown loop in blockwise tests."

Hi,

While we are testing fs with xfstests, generic/108 will fail at some 
times with the reson that rmmod find the refcnt of scsi_debug module 
isn't 0 by checking /proc/modules. And this your patch is really 
describe the same thing. But, i am confusing about the scene as you said:
  cleanup() {
         if [ -d "$MNT_DIR" ] ; then
             umount -f $MNT_DIR 2>/dev/null
             rmdir $MNT_DIR 2>/dev/null
         fi
         rm -f $LOCAL_FILE 2> /dev/null
-       udevadm settle >/dev/null 2>&1
-       rmmod scsi_debug 2> /dev/null
+       scsi_debug_teardown "$DEV" || exit 100
  }

After the settle, all the event has been finish, so who will trigger the 
scan, and how to scan? Can you help to explain this? Thanks a lot!

Thanks,
Kun.