Try to reproduce it via libvirt.
Version:
libvirt-1.3.4-1.el7.x86_64
qemu-kvm-rhev-2.6.0-2.el7.x86_64

Step:
1. Start a guest with image on NFS storage
# virsh list 
 Id    Name                           State
----------------------------------------------------
 2     r72                            running

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

I want to know when it will hang on virDomainGetControlInfo(). So I tried this :
#!/bin/bash
while :
do 
virsh domcontrol r72
sleep 30
done

3. on terminal 1, check IO throughttling with the image.
# virsh domblklist r72
Target     Source
------------------------------------------------
hda        -
vda        /tmp/zp/r7.2.img

# virsh blkdeviotune r72 vda 

......hang here

log as following :
......
2016-05-24 01:50:16.712+0000: 2512: debug : qemuDomainObjBeginJobInternal:2097 : Starting job: query (vm=0x7fe7501f2d40 name=r72, current job=query async=none)
2016-05-24 01:50:16.712+0000: 2512: debug : qemuDomainObjBeginJobInternal:2120 : Waiting for job (vm=0x7fe7501f2d40 name=r72)
2016-05-24 01:50:17.666+0000: 1309: info : virObjectRef:296 : OBJECT_REF: obj=0x7fe7d0a34300
......

4.change to termianl 2, check other info, it works well
# virsh list 
 Id    Name                           State
----------------------------------------------------
 2     r72                            running

# virsh schedinfo r72
Scheduler      : posix
cpu_shares     : 1024
vcpu_period    : 100000
vcpu_quota     : -1
emulator_period: 100000
emulator_quota : -1
global_period  : 100000
global_quota   : -1


5. change to terminal 3. check block stat info, it will hang for a few seconds, then it will report an error.
# virsh domblkstat r72 
(hang a few seconds)
error: Timed out during operation: cannot acquire state change lock (held by remoteDispatchDomainGetBlockIoTune)

log as following :
......
2016-05-24 01:50:46.698+0000: 1309: info : virObjectUnref:259 : OBJECT_UNREF: obj=0x7fe7d0a47970
2016-05-24 01:50:46.712+0000: 2512: warning : qemuDomainObjBeginJobInternal:2180 : Cannot start job (query, none) for domain r72; current job is (query, none) owned by (2513 remoteDispatchDomainGetBlockIoTune, 0 <null>) for (41s, 0s)
2016-05-24 01:50:46.712+0000: 2512: error : qemuDomainObjBeginJobInternal:2192 : Timed out during operation: cannot acquire state change lock (held by remoteDispatchDomainGetBlockIoTune)
......

2016-05-24 01:45:32.325+0000: 2514: debug : virThreadJobSet:96 : Thread 2514 (virNetServerHandleJob) is now running job remoteDispatchDomainGetInfo
2016-05-24 01:45:32.325+0000: 2514: info : virObjectNew:202 : OBJECT_NEW: obj=0x7fe7a403d340 classname=virDomain
......
2016-05-24 01:45:32.325+0000: 2514: debug : virThreadJobClear:121 : Thread 2514 (virNetServerHandleJob) finished job remoteDispatchDomainGetInfo with ret=0
......

6. It seems that it will hang in the terminal 1:
# virsh blkdeviotune r72 vda 
...... hang here, nothing output.

but virsh list or other checkinfo except block related works well. 

7.If I Ctrl+c terminal this command and re-try it again:
# virsh blkdeviotune r72 vda
^C
# 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)


As above, Do these steps can be used to reproduce this issue? It will hang in step6 and step7.