How do you force a CIFS connection to unmount

Error:
When trying to umount the cifs windows shared mount point getting below error even after killing using fuser output.

umount /tmp

umount lsof: WARNING: can't stat() cifs file system /mnt
      Output information may be incomplete.
lsof: status error on /mnt: No such device

Soluiton:
Use force un mount.

umount -f -a -t cifs -l /mnt/