$ ./python -m test -j2 test__xxsubinterpreters test__xxsubinterpreters -m test_already_running -v (...) == Python build: debug TraceRefs (...) == CPU count: 12 (...) 0:00:00 load avg: 1.19 Run tests in parallel using 2 child processes 0:00:00 load avg: 1.19 [1/2] test__xxsubinterpreters passed test_already_running (test.test__xxsubinterpreters.RunStringTests.test_already_running) ... ok (...) 0:00:00 load avg: 1.19 [2/2/1] test__xxsubinterpreters crashed (Exit code -6) test_already_running (test.test__xxsubinterpreters.RunStringTests.test_already_running) ... Objects/object.c:2235: _Py_ForgetReference: Assertion failed: invalid object chain Enable tracemalloc to get the memory block allocation traceback object address : 0x7f01d0be95a0 object refcount : 0 object type : 0xa1dc00 object type name: str object repr : <refcnt 0 at 0x7f01d0be95a0> Fatal Python error: _PyObject_AssertFailed: _PyObject_AssertFailed Python runtime state: initialized Current thread 0x00007f01df4a1740 (most recent call first): <no Python frame> (...) 

git clean -fdx ./configure --with-pydebug --with-trace-refs CFLAGS="-O0" make -j14