Comment 46 for bug 624877

I also experience this behaviour on 10.04 with kernel linux-image-generic-lts-backport-natty :

Linux quantus 2.6.38-13-generic #57~lucid1-Ubuntu SMP Tue Mar 6 20:05:46 UTC 2012 x86_64 GNU/Linux

Apparently, Virtualbox is the culprit on my system. I have virtual machines on a ext4 RAID1. When this dpkg became stuck the last time, I was able to track it down to virtualbox keeping jdb2 busy. Once I stopped the VM, sync and dpkg finished normally.