'unregister_netdevice: waiting for lo to become free. Usage count = 2' is reported and causing kernel hang when floodlight tests are run using utah

When utah client is used to run floodlight smoke tests for saucy server images, the following error is reported.

May 13 03:51:09 utah-8671-saucy-server-i386 kernel: [ 154.327421] IPv6: ADDRCONF(NETDEV_UP): s1-eth1: link is not ready
May 13 03:51:19 utah-8671-saucy-server-i386 kernel: [ 164.100031] unregister_netdevice: waiting for lo to become free. Usage count = 2
...
...
May 13 03:54:33 utah-8671-saucy-server-i386 kernel: [ 358.452029] unregister_netdevice: waiting for lo to become free. Usage count = 2
May 13 03:54:35 utah-8671-saucy-server-i386 kernel: [ 360.636063] INFO: task mnexec:7033 blocked for more than 120 seconds.
May 13 03:54:35 utah-8671-saucy-server-i386 kernel: [ 360.636071] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
May 13 03:54:35 utah-8671-saucy-server-i386 kernel: [ 360.636076] mnexec D 000000f2 0 7033 6369 0x00000000
May 13 03:54:35 utah-8671-saucy-server-i386 kernel: [ 360.636081] de407f00 00000082 dffe7c20 000000f2 d1655300 0016eb12 00000000 c19cc3c0
May 13 03:54:35 utah-8671-saucy-server-i386 kernel: [ 360.636086] 00000000 00000023 c19cc3c0 dfbf23c0 dee42670 dfc56240 d1655300 00000000
May 13 03:54:35 utah-8671-saucy-server-i386 kernel: [ 360.636089] ded99540 00000000 b7666550 d1655300 02d12067 c2c7edd8 d1655300 de407f14
May 13 03:54:35 utah-8671-saucy-server-i386 kernel: [ 360.636092] Call Trace:
May 13 03:54:35 utah-8671-saucy-server-i386 kernel: [ 360.636113] [<c112e69a>] ? handle_mm_fault+0x22a/0x310
May 13 03:54:35 utah-8671-saucy-server-i386 kernel: [ 360.636126] [<c160efc3>] schedule_preempt_disabled+0x23/0x60
May 13 03:54:35 utah-8671-saucy-server-i386 kernel: [ 360.636129] [<c160d553>] __mutex_lock_slowpath+0xb3/0x110
May 13 03:54:35 utah-8671-saucy-server-i386 kernel: [ 360.636131] [<c160d10c>] mutex_lock+0x1c/0x30
May 13 03:54:35 utah-8671-saucy-server-i386 kernel: [ 360.636144] [<c1525944>] copy_net_ns+0x54/0xd0
May 13 03:54:35 utah-8671-saucy-server-i386 kernel: [ 360.636153] [<c106ec81>] create_new_namespaces+0xd1/0x150
May 13 03:54:35 utah-8671-saucy-server-i386 kernel: [ 360.636156] [<c106ee7e>] unshare_nsproxy_namespaces+0x4e/0x90
May 13 03:54:35 utah-8671-saucy-server-i386 kernel: [ 360.636164] [<c1049697>] sys_unshare+0x127/0x230
May 13 03:54:35 utah-8671-saucy-server-i386 kernel: [ 360.636170] [<c1612ba0>] ? arch_prepare_kprobe_ftrace+0x20/0x20
May 13 03:54:35 utah-8671-saucy-server-i386 kernel: [ 360.636174] [<c1616b4d>] sysenter_do_call+0x12/0x28
...
================================================
This is observed to occur only when utah is used to run the floodlight smoke tests. Running the floodlight tests without utah does not cause this issue and using utah to run some other tests does not cause this issue either.

Noticed a similar bug 1021471, but this one is occurring in KVM using libvirt.

The issue is only with the saucy kernel version, 3.9.0-1 and does not occur with 3.9.0-0. The tests were tried with saucy server VMs on precise as well as saucy hosts and the results is the same.

Steps to reproduce:
1. Install a default saucy server on a vm (either manually or preseeded default installation) with either i386 or amd64 image using KVM, libvirt
2. Do the following to install utah inside the VM
   sudo apt-add-repository -y ppa:utah/stable
   sudo apt-get update
   sudo apt-get install utah
3. Run the floodlight tests using
     sudo utah -r lp:ubuntu-test-cases/server/runlists/floodlight.run
4. Now "kernel: [ 358.452029] unregister_netdevice: waiting for lo to become free. Usage count = 2" will be continuously reported

Install and boot time syslogs are attached.

The impacted jobs are,
https://jenkins.qa.ubuntu.com/view/Saucy/view/Smoke%20Testing/job/saucy-server-amd64-smoke-floodlight/15/
and
https://jenkins.qa.ubuntu.com/view/Saucy/view/Smoke%20Testing/job/saucy-server-i386-smoke-floodlight/13/