unmounted logical volume is "busy"?

I'm trying to shrink an ext4 filesystem on a CentOS 6 server. I did a lazy unmount of the filesystem while I waited for some processes to finish running. They've all finished running but I can't seem to do anything with the filesystem. How can I see what is using the volume and stop it?

resize2fs

[root@planck ~]# resize2fs -P /dev/vg_dev/lv_home 
resize2fs 1.42.9 (28-Dec-2013)
resize2fs: Device or resource busy while trying to open /dev/vg_dev/lv_home
Couldn't find valid filesystem superblock.

fsck

[root@planck ~]# fsck /dev/vg_dev/lv_home 
fsck from util-linux-ng 2.17.2
e2fsck 1.42.9 (28-Dec-2013)
/dev/mapper/vg_dev-lv_home is in use.
e2fsck: Cannot continue, aborting.

umount

[root@planck ~]# umount /dev/vg_dev/lv_home
umount: /dev/vg_dev/lv_home: not mounted

lvs

  LV      VG     Attr       LSize  Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  lv_home vg_dev -wi-ao----  5.86t                                                    
  lv_root vg_dev -wi-ao---- 50.00g                                                    
  lv_swap vg_dev -wi-ao----  5.44g                                                    

Solution 1:

fuser -mv /dev/vg_dev/lv_home should show you the process PID you need to kill to free up the device.

For example:

 # fuser -mv /dev/vg_dev/lv_home
                         USER        PID ACCESS COMMAND
    /dev/vg_dev/lv_home:
                         sbonds     9627 ..c.. bash

Now, you may not be able to actually kill it if it's blocked on I/O or some other uninterruptible reason.