I can get an intermittent (1 every 15 or so runs) lock in:
 test_get (__main__.WithProcessesTestQueue) ... 

Executed like this:
./python Lib/test/test_multiprocessing.py

When I control-c it the stack looks like this:
...snip
  File "/root/py/python-3000/Lib/multiprocessing/pool.py", line 57, in 
worker
    task = get()
  File "/root/py/python-3000/Lib/multiprocessing/queues.py", line 337, 
in get
    task = get()
  File "/root/py/python-3000/Lib/multiprocessing/queues.py", line 339, 
in get
    racquire()
KeyboardInterrupt
    task = get()
  File "/root/py/python-3000/Lib/multiprocessing/queues.py", line 337, 
in get
    task = get()
  File "/root/py/python-3000/Lib/multiprocessing/queues.py", line 337, 
in get
    return recv()
  File "/root/py/python-3000/Lib/pickle.py", line 1327, in loads
    racquire()
KeyboardInterrupt
    racquire()
KeyboardInterrupt
    def loads(s, *, encoding="ASCII", errors="strict"):
KeyboardInterrupt


I'm not seeing frequent locks/failures when run with regrtest, but I am 
seeing them with "make test TESTOPTS=test_multiprocessing"

I've attached full output. Still trying to figure it out