Comment 12 for bug 1746630

Thanks a lot for Peter's info. and reproduce it like following :
version:
libvirt-1.3.4-1.el7.x86_64

steps:
1. start a guest with image on NFS storage
# virsh list
 Id Name State
----------------------------------------------------
 20 r72 running

2. Disconnect with NFS server
# iptables -A OUTPUT -d $IP -p tcp --dport 2049 -j DROP
#

3. In terminal 1, execute 'blkdeviotune'

# virsh blkdeviotune r72 vda

4.in terminal 2, try 'domstats' to get statistices for all domains.
# virsh domstats

5. After few seconds, in terminal 1, we can get an error
# virsh blkdeviotune r72 vda
error: Unable to get number of block I/O throttle parameters
error: Timed out during operation: cannot acquire state change lock (held by remoteDispatchDomainGetBlockIoTune)

6. check termianl 2, virsh domstats still hang

# virsh domstats
......hang here

7. in terminal 3, check virsh list, it will also hang
#virsh list
...... hang here.

Actual results:
As step 6 and step 7, virsh domstats hang and listing guest also hang.

Expected results:
It should return less data for active VMs and won't hang.