Comment 2 for bug 1046313

 kernel: we applied a patch for lxc tool support to 2.6.38. We use RHEL 6.2.

$ uname -a
Linux bespin101 2.6.38.2-lxc-0.7.4 #3 SMP Fri Dec 2 15:58:39 EST 2011 x86_64 x86_64 x86_64 GNU/Linux

 About race condition, sorry for the confusion.
I believe it is not unmounted at all.
But, I don't see error message of "Failed to unmount ...".
So, I think it fails to unmount but does not report error.

 As I mentioned before,
I can unmount the rootfs and disconnect nbd device manually later.