Cannot umount: device is busy

[T o n g <mlist4suntong@yahoo.com>]

Hi, 

I can't umount a device even I've killed all related processes:

  % umount /mnt/mpoint
  umount: /mnt/mpoint: device is busy.
	  (In some cases useful info about processes that use
	   the device is found by lsof(8) or fuser(1))

  % fuser -vm /mnt/mpoint
		       USER        PID ACCESS COMMAND
  /mnt/mpoint:         root     kernel mount /mnt/mpoint
		       root     kernel knfsd /mnt/mpoint

I.e., there is no processes associated with the mount point any more,
but I still can't umount the device. Moreover:

  $ ps -eaf | grep knfs[d] || echo no found 
  no found

I.e., there isn't such task as knfsd in ps list. Why is that?

Is there any way that I can kill all those kernel processes associated
with the mount?

Thanks

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