This started to bother us in Fedora for various Python versions, so chances are something changed on the system level.

However for us it seams test_multiprocessing_fork hangs by itself, so this might or might not be relevant to 


# python3.7 -m test.regrtest test_multiprocessing_fork test_subprocess
Run tests sequentially
0:00:00 load avg: 1.16 [1/2] test_multiprocessing_fork
/usr/lib64/python3.7/multiprocessing/semaphore_tracker.py:55: UserWarning: semaphore_tracker: process died unexpectedly, relaunching.  Some semaphores might leak.
  warnings.warn('semaphore_tracker: process died unexpectedly, '
Exception in thread Thread-26:
Traceback (most recent call last):
  File "/usr/lib64/python3.7/threading.py", line 917, in _bootstrap_inner
    self.run()
  File "/usr/lib64/python3.7/threading.py", line 865, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/lib64/python3.7/multiprocessing/resource_sharer.py", line 139, in _serve
    signal.pthread_sigmask(signal.SIG_BLOCK, range(1, signal.NSIG))
  File "/usr/lib64/python3.7/signal.py", line 60, in pthread_sigmask
    sigs_set = _signal.pthread_sigmask(how, mask)
ValueError: signal number 32 out of range

(hangs)

^CProcess Process-184:
Traceback (most recent call last):
  File "/usr/lib64/python3.7/multiprocessing/process.py", line 297, in _bootstrap
    self.run()
  File "/usr/lib64/python3.7/multiprocessing/process.py", line 99, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/lib64/python3.7/test/_test_multiprocessing.py", line 3328, in child_access
    w = conn.recv()
  File "/usr/lib64/python3.7/multiprocessing/connection.py", line 251, in recv
    return _ForkingPickler.loads(buf.getbuffer())
  File "/usr/lib64/python3.7/multiprocessing/connection.py", line 960, in rebuild_connection
    fd = df.detach()
  File "/usr/lib64/python3.7/multiprocessing/resource_sharer.py", line 57, in detach
    with _resource_sharer.get_connection(self._id) as conn:
  File "/usr/lib64/python3.7/multiprocessing/resource_sharer.py", line 87, in get_connection
    c = Client(address, authkey=process.current_process().authkey)
  File "/usr/lib64/python3.7/multiprocessing/connection.py", line 498, in Client
    answer_challenge(c, authkey)
  File "/usr/lib64/python3.7/multiprocessing/connection.py", line 741, in answer_challenge
    message = connection.recv_bytes(256)         # reject large message
  File "/usr/lib64/python3.7/multiprocessing/connection.py", line 216, in recv_bytes
    buf = self._recv_bytes(maxlength)
  File "/usr/lib64/python3.7/multiprocessing/connection.py", line 407, in _recv_bytes
    buf = self._recv(4)
  File "/usr/lib64/python3.7/multiprocessing/connection.py", line 379, in _recv
    chunk = read(handle, remaining)
KeyboardInterrupt
Warning -- multiprocessing.process._dangling was modified by test_multiprocessing_fork
  Before: <_weakrefset.WeakSet object at 0x7f4b63782dd8>
  After:  <_weakrefset.WeakSet object at 0x7f4b637821d0> 
Warning -- threading._dangling was modified by test_multiprocessing_fork
  Before: <_weakrefset.WeakSet object at 0x7f4b63782780>
  After:  <_weakrefset.WeakSet object at 0x7f4b63782da0> 

Test suite interrupted by signal SIGINT.
2 tests omitted:
    test_multiprocessing_fork test_subprocess

Total duration: 1 min 35 sec
Tests result: INTERRUPTED

# python3.7 --version
Python 3.7.0b3


# python3.6 -m test.regrtest test_multiprocessing_fork test_subprocess
Run tests sequentially
0:00:00 load avg: 1.84 [1/2] test_multiprocessing_fork
/usr/lib64/python3.6/multiprocessing/semaphore_tracker.py:55: UserWarning: semaphore_tracker: process died unexpectedly, relaunching.  Some semaphores might leak.
  warnings.warn('semaphore_tracker: process died unexpectedly, '
Exception in thread Thread-20:
Traceback (most recent call last):
  File "/usr/lib64/python3.6/threading.py", line 916, in _bootstrap_inner
    self.run()
  File "/usr/lib64/python3.6/threading.py", line 864, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/lib64/python3.6/multiprocessing/resource_sharer.py", line 139, in _serve
    signal.pthread_sigmask(signal.SIG_BLOCK, range(1, signal.NSIG))
  File "/usr/lib64/python3.6/signal.py", line 60, in pthread_sigmask
    sigs_set = _signal.pthread_sigmask(how, mask)
ValueError: signal number 32 out of range

(hangs)

^CProcess Process-178:
Traceback (most recent call last):
...
KeyboardInterrupt
Warning -- multiprocessing.process._dangling was modified by test_multiprocessing_fork
  Before: <_weakrefset.WeakSet object at 0x7f1873917c88>
  After:  <_weakrefset.WeakSet object at 0x7f188516d978> 
Warning -- threading._dangling was modified by test_multiprocessing_fork
  Before: <_weakrefset.WeakSet object at 0x7f1873917d68>
  After:  <_weakrefset.WeakSet object at 0x7f1873917e48> 

Test suite interrupted by signal SIGINT.
2 tests omitted:
    test_multiprocessing_fork test_subprocess

Total duration: 51 sec
Tests result: INTERRUPTED

# python3.6 --version
Python 3.6.5


# python3.5 -m test.regrtest test_multiprocessing_fork test_subprocess
0:00:00 load avg: 1.83 [1/2] test_multiprocessing_fork
Exception in thread Thread-20:
Traceback (most recent call last):
  File "/usr/lib64/python3.5/threading.py", line 914, in _bootstrap_inner
    self.run()
  File "/usr/lib64/python3.5/threading.py", line 862, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/lib64/python3.5/multiprocessing/resource_sharer.py", line 139, in _serve
    signal.pthread_sigmask(signal.SIG_BLOCK, range(1, signal.NSIG))
  File "/usr/lib64/python3.5/signal.py", line 60, in pthread_sigmask
    sigs_set = _signal.pthread_sigmask(how, mask)
ValueError: signal number 32 out of range

(hangs)

^CProcess Process-178:
Traceback (most recent call last):
...
KeyboardInterrupt
Warning -- multiprocessing.process._dangling was modified by test_multiprocessing_fork
  Before: <_weakrefset.WeakSet object at 0x7f2bb3923ba8>
  After:  <_weakrefset.WeakSet object at 0x7f2bc4d88b38> 
Warning -- threading._dangling was modified by test_multiprocessing_fork
  Before: <_weakrefset.WeakSet object at 0x7f2bb3923be0>
  After:  <_weakrefset.WeakSet object at 0x7f2bb3923f28> 

Test suite interrupted by signal SIGINT.
2 tests omitted:
    test_multiprocessing_fork test_subprocess
Tests result: INTERRUPTED

# python3.5 --version
Python 3.5.4

# python3.4 -m test.regrtest test_multiprocessing_fork test_subprocess
[1/2] test_multiprocessing_fork
Exception in thread Thread-21:
Traceback (most recent call last):
  File "/usr/lib64/python3.4/threading.py", line 911, in _bootstrap_inner
    self.run()
  File "/usr/lib64/python3.4/threading.py", line 859, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/lib64/python3.4/multiprocessing/resource_sharer.py", line 139, in _serve
    signal.pthread_sigmask(signal.SIG_BLOCK, range(1, signal.NSIG))
ValueError: signal number 32 out of range

(hangs)

^CTraceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib64/python3.4/multiprocessing/forkserver.py", line 170, in main
Warning -- multiprocessing.process._dangling was modified by test_multiprocessing_fork
Warning -- threading._dangling was modified by test_multiprocessing_fork
Process Process-180:
Traceback (most recent call last):
...
KeyboardInterrupt

Test suite interrupted by signal SIGINT.
2 tests omitted:
    test_multiprocessing_fork test_subprocess

# python3.4 --version
Python 3.4.8