Xen users - Sep 2012 - hang when umount right after write big data

it hangs when umount right after wite big data in dom0

i tried step like below

mkdir mnt
truncate --size 2G image.img
mount -o loop image.img mnt
cd mnt
cp rootfs.tar.gz .
tar -xvzf rootfs.tar.gz (this file size is around 1G )
cd ..
umount mnt

and it hangs

if I try umount after i wait 30 seconds or more. it could be done.

any opinion about this?

it doesn''t happened when i tried on linux machine not dom0

thanks