Description of problem:
start vm with 2 disk. 1st disk is block device and 2th disk's image is on nfs file, do live migration and cp files to 2th disk. migration will hang.

Version-Release number of selected component (if applicable):
# uname -r
2.6.18-269.el5
# rpm -qa|grep kvm
kvm-83-238.el5

How reproducible:
100%

Steps to Reproduce:
1. create a image on nfs file as 2th disk 
 #qemu-img create -f qcow2 /mnt/tt 40G

2.# /usr/libexec/qemu-kvm -no-hpet -usbdevice tablet -rtc-td-hack -name 61 -smp 2 -m 4G -uuid 9e6f04cf-2ad7-45aa-9333-2d2ee26570c6 -boot c -drive file=/dev/chayang/chayang1,if=virtio,cache=none,boot=on,format=qcow2,werror=stop -net nic,vlan=1,macaddr=52:54:00:94:a3:8b,model=virtio -net tap,vlan=1,script=/etc/qemu-ifup -notify all -balloon none -monitor stdio -vnc :1  -drive file=/mnt/tt,if=virtio,werror=stop,cache=none,format=qcow2,cache=none

3.# /usr/libexec/qemu-kvm -no-hpet -usbdevice tablet -rtc-td-hack -name 61 -smp 2 -m 4G -uuid 9e6f04cf-2ad7-45aa-9333-2d2ee26570c6 -boot c -drive file=/dev/chayang/chayang1,if=virtio,cache=none,boot=on,format=qcow2,werror=stop -net nic,vlan=1,macaddr=52:54:00:94:a3:8b,model=virtio -net tap,vlan=1,script=/etc/qemu-ifup -notify all -balloon none -monitor stdio -vnc :1  -drive file=/mnt/tt,if=virtio,werror=stop,cache=none,format=qcow2,cache=none -incoming tcp:0:5555

4. format 2th disk and mount it to /mnt in guest

5. cp file to /mnt/ in guest

6. do migrate 
  
Actual results:
migration hang

Expected results:
migrate successful

Additional info: