I've never seen a process in so-called uninterruptible sleep status.
That might happen because of some NFS-related I/O, but it's
improbable to find where it can be in my scenario. The only idea I
have is that when I run a `subprocess.call(..., shell=True)` it
starts an interactive shell which in its turn reads some config files
from my home folder (like `.profile` or `.bashrc`). And my home
directory is NFS-mounted to all the lab servers. So if it suddenly
goes down, that makes the whole thing became sleeping forever. I
tried to change these calls by simple `os.system`, and it worked.
