Unable to unmount NFSv3 or NFSv4 mounts when mounted using IPv6 address

[Scott Duckworth]

I am unable to unmount NFS (v3 or v4) mount points if they were mounted using the server's IPv6 address instead of the server's hostname (which resolves to an IPv6 address). umount says "<mountpoint> was not found in /proc/mounts" even though the file system is clearly mounted.

I do not get the expected result when using IPv6 addresses (NFSv3 example):

root@gecko23:~# mount -t nfs [2620:103:a000:401::1:9]:/vol/public /mnt2
root@gecko23:~# mount | grep /mnt2
[2620:103:a000:401::1:9]:/vol/public on /mnt2 type nfs (rw,vers=4,addr=2620:103:a000:401::1:9,clientaddr=2620:103:a000:401:7880:a21c:f25:d073)
root@gecko23:~# cat /proc/mounts | grep /mnt2
2620:103:a000:401::1:9:/vol/public/ /mnt2 nfs4 rw,relatime,vers=4,rsize=65536,wsize=65536,namlen=255,hard,proto=tcp6,port=0,timeo=600,retrans=2,sec=sys,clientaddr=2620:103:a000:401:7880:a21c:f25:d073,minorversion=0,local_lock=none,addr=2620:103:a000:401::1:9 0 0
root@gecko23:~# umount /mnt2
/mnt2 was not found in /proc/mounts
/mnt2 was not found in /proc/mounts

This problem also happens when using NFSv4.

When mounting using a hostname which resolves to an IPv6 address, I get the expected result (NFSv4 example):

root@gecko23:~# mount -t nfs4 netapp2a-v6.cs.clemson.edu:/vol/public /mnt2
root@gecko23:~# mount | grep /mnt2
netapp2a-v6.cs.clemson.edu:/vol/public on /mnt2 type nfs4 (rw,addr=2620:103:a000:401::1:9,clientaddr=2620:103:a000:401:7880:a21c:f25:d073)
root@gecko23:~# cat /proc/mounts | grep /mnt2
netapp2a-v6.cs.clemson.edu:/vol/public/ /mnt2 nfs4 rw,relatime,vers=4,rsize=65536,wsize=65536,namlen=255,hard,proto=tcp6,port=0,timeo=600,retrans=2,sec=sys,clientaddr=2620:103:a000:401:7880:a21c:f25:d073,minorversion=0,local_lock=none,addr=2620:103:a000:401::1:9 0 0
root@gecko23:~# umount /mnt2

Using a hostname with NFSv3 works as expected too:

root@gecko23:~# mount -t nfs netapp2a-v6.cs.clemson.edu:/vol/public /mnt2
root@gecko23:~# umount /mnt2

Perhaps the colons (':') in the IPv6 addresses get confused with the delimiter (a colon) between NFS server and share point?

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: mount 2.20.1-1ubuntu3
ProcVersionSignature: Ubuntu 3.2.0-23.36-generic 3.2.14
Uname: Linux 3.2.0-23-generic x86_64
ApportVersion: 2.0.1-0ubuntu7
Architecture: amd64
Date: Wed May 16 08:20:50 2012
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
ProcEnviron:
 TERM=xterm
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: util-linux
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.