Hi,

test_socket started to hang recently on my Fedora 28 laptop. No idea why it started to hang.

vstinner@apu$ ./python -m test -v test_socket -m testCongestion --timeout=5
== CPython 3.8.0a0 (heads/master-dirty:39487196c8, Sep 4 2018, 23:08:20) [GCC 8.1.1 20180712 (Red Hat 8.1.1-5)]
== Linux-4.17.19-200.fc28.x86_64-x86_64-with-glibc2.26 little-endian
== cwd: /home/vstinner/prog/python/master/build/test_python_29510
== CPU count: 8
== encodings: locale=UTF-8, FS=utf-8
Run tests sequentially
0:00:00 load avg: 1.34 [1/1] test_socket
testCongestion (test.test_socket.RDSTest) ... Timeout (0:00:05)!
Thread 0x00007fccf51b1700 (most recent call first):
  File "/home/vstinner/prog/python/master/Lib/test/test_socket.py", line 2074 in _testCongestion
  File "/home/vstinner/prog/python/master/Lib/test/test_socket.py", line 332 in clientRun

Thread 0x00007fcd082ee080 (most recent call first):
  File "/home/vstinner/prog/python/master/Lib/threading.py", line 296 in wait
  File "/home/vstinner/prog/python/master/Lib/threading.py", line 552 in wait
  File "/home/vstinner/prog/python/master/Lib/test/test_socket.py", line 2059 in testCongestion
  File "/home/vstinner/prog/python/master/Lib/unittest/case.py", line 610 in run
  File "/home/vstinner/prog/python/master/Lib/unittest/case.py", line 658 in __call__
  File "/home/vstinner/prog/python/master/Lib/unittest/suite.py", line 122 in run
  File "/home/vstinner/prog/python/master/Lib/unittest/suite.py", line 84 in __call__
  File "/home/vstinner/prog/python/master/Lib/unittest/suite.py", line 122 in run
  File "/home/vstinner/prog/python/master/Lib/unittest/suite.py", line 84 in __call__
  File "/home/vstinner/prog/python/master/Lib/unittest/runner.py", line 176 in run
  File "/home/vstinner/prog/python/master/Lib/test/support/__init__.py", line 1900 in _run_suite
  File "/home/vstinner/prog/python/master/Lib/test/support/__init__.py", line 1990 in run_unittest
  File "/home/vstinner/prog/python/master/Lib/test/test_socket.py", line 6032 in test_main
  File "/home/vstinner/prog/python/master/Lib/test/libregrtest/runtest.py", line 179 in runtest_inner
  File "/home/vstinner/prog/python/master/Lib/test/libregrtest/runtest.py", line 140 in runtest
  File "/home/vstinner/prog/python/master/Lib/test/libregrtest/main.py", line 384 in run_tests_sequential
  File "/home/vstinner/prog/python/master/Lib/test/libregrtest/main.py", line 488 in run_tests
  File "/home/vstinner/prog/python/master/Lib/test/libregrtest/main.py", line 566 in _main
  File "/home/vstinner/prog/python/master/Lib/test/libregrtest/main.py", line 531 in main
  File "/home/vstinner/prog/python/master/Lib/test/libregrtest/main.py", line 584 in main
  File "/home/vstinner/prog/python/master/Lib/test/__main__.py", line 2 in <module>
  File "/home/vstinner/prog/python/master/Lib/runpy.py", line 85 in _run_code
  File "/home/vstinner/prog/python/master/Lib/runpy.py", line 193 in _run_module_as_main