Unable to unmount ext4 filesystem due to "device is busy" error

Solution Unverified - Updated -

Issue

  • Filesystem not getting umount
# umount /mountpoint/
umount: /mountpoint: device is busy.
        (In some cases useful info about processes that use
         the device is found by lsof(8) or fuser(1))

Environment

  • Red Hat Enterprise Linux 6.2
    • seen with kernel 2.6.32-504.1.3.el6 (RHEL6.6)
  • Ext4
    • LVM linear LV with single device (sdb)
    • iSCSI device
  • 3rd party kernel module: CommVault Continuous Data Replicator
cdr: module license 'CommVault Systems' taints kernel.
Disabling lock debugging due to kernel taint
cdr module is older than RHEL 6.2 ... applying fixups
2671: fsf_init(): Initializing the driver.
2671: fsf_init(): Built: Nov 21 2013 10:56:12
em4: no IPv6 routers present
2686: cxfs_init(): Initializing CXFS subsystem
2686: cxfs_novell_init(): Non-OES Kernel detected.
2686: cdr_init(): Initializing CDR subsystem

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