When using NFSv4 on Fedora 20 with latest kernel (3.15.0-rc6+),
I can't umount the mountpoint after only an 'ls' operation.
[root@localhost ~]# cat /etc/exports
/nfstest *(rw,no_root_squash,no_subtree_check,insecure)
[root@localhost ~]# mount -t nfs 127.0.0.1:/ /mnt/
[root@localhost ~]# ls /mnt/
nfstest
[root@localhost ~]# umount /mnt/
umount.nfs4: /mnt: device is busy