Failure at revision 636fa01842f597bedff7054616c65a4784c92b4a on AMD64 Windows10 3.x (regrtest runs without the -j option, so all tests are run in the same thread).

http://buildbot.python.org/all/builders/AMD64%20Windows10%203.x/builds/763/steps/test/logs/stdio
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0:12:37 [ 87/400/1] test_tracemalloc
[pid 2864, tid 2624] tracemalloc_start()
[pid 2864, tid 2624] tracemalloc_init()
[pid 2864, tid 2624] tracemalloc_init(): exit (already initialized)
Assertion failed: get_reentrant(), file ..\Modules\_tracemalloc.c, line 1057
Fatal Python error: Aborted

Current thread 0x00000a40 (most recent call first):
  File "D:\buildarea\3.x.bolen-windows10\build\lib\test\test_tracemalloc.py", line 97 in setUp
  File "D:\buildarea\3.x.bolen-windows10\build\lib\unittest\case.py", line 596 in run
  File "D:\buildarea\3.x.bolen-windows10\build\lib\unittest\case.py", line 648 in __call__
  File "D:\buildarea\3.x.bolen-windows10\build\lib\unittest\suite.py", line 122 in run
  File "D:\buildarea\3.x.bolen-windows10\build\lib\unittest\suite.py", line 84 in __call__
  File "D:\buildarea\3.x.bolen-windows10\build\lib\unittest\suite.py", line 122 in run
  File "D:\buildarea\3.x.bolen-windows10\build\lib\unittest\suite.py", line 84 in __call__
  File "D:\buildarea\3.x.bolen-windows10\build\lib\unittest\runner.py", line 176 in run
  File "D:\buildarea\3.x.bolen-windows10\build\lib\test\support\__init__.py", line 1802 in _run_suite
  File "D:\buildarea\3.x.bolen-windows10\build\lib\test\support\__init__.py", line 1836 in run_unittest
  File "D:\buildarea\3.x.bolen-windows10\build\lib\test\test_tracemalloc.py", line 999 in test_main
  File "D:\buildarea\3.x.bolen-windows10\build\lib\test\libregrtest\runtest.py", line 162 in runtest_inner
  File "D:\buildarea\3.x.bolen-windows10\build\lib\test\libregrtest\runtest.py", line 115 in runtest
  File "D:\buildarea\3.x.bolen-windows10\build\lib\test\libregrtest\main.py", line 306 in run_tests_sequential
  File "D:\buildarea\3.x.bolen-windows10\build\lib\test\libregrtest\main.py", line 367 in run_tests
  File "D:\buildarea\3.x.bolen-windows10\build\lib\test\libregrtest\main.py", line 405 in main
  File "D:\buildarea\3.x.bolen-windows10\build\lib\test\libregrtest\main.py", line 446 in main
  File "D:\buildarea\3.x.bolen-windows10\build\lib\test\libregrtest\main.py", line 468 in main_in_temp_cwd
  File "D:\buildarea\3.x.bolen-windows10\build\PCbuild\..\lib\test\regrtest.py", line 39 in <module>
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I understand that tracemalloc_start() was called with the first time and that get_reentrant() returns 0 at tracemalloc_start() entry, whereas tracemalloc_init() is supposed to set the reentrant flag to 1.