A new bug, introduced in recent Python 2.7 (2.7.3 passes, 2.7 trunk fails):

With the attached x.py, running "python -c 'import x'" fails with RuntimeError: not holding the import lock.

It occurs when doing a fork() while holding the import lock, if the child process imports more things (here distutils, could be anything) before finally trying to release the import lock (here by returning from the original 'import x').