"Skipping pudb interrupt support"

I'm trying to use `pudb` for OpenStack (Cinder).

Inserting the `import pudb; pudb.set_trace()` snippet doesn't work; I only get

```
/usr/lib/python2.7/dist-packages/pudb/__init__.py:192: UserWarning:
A non-default handler for signal 2 is already installed (1).
Skipping pudb interrupt support.
% (interrupt_signal, old_handler))
```

Ain't there a way to _unconditionally_ break into pudb?