This is 3.6.7, compiled --with-pydebug:


$ ./main 
Aborted (core dumped)



(gdb) bt
#0  0x00007f9974077428 in __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:54
#1  0x00007f997407902a in __GI_abort () at abort.c:89
#2  0x000000000056e2d1 in Py_FatalError (msg=msg@entry=0x62ccf8 "Python memory allocator called without holding the GIL") at Python/pylifecycle.c:1462
#3  0x00000000004c0cec in _PyMem_DebugCheckGIL () at Objects/obmalloc.c:1963
#4  0x00000000004c0d27 in _PyMem_DebugMalloc (ctx=0x8f7220 <_PyMem_Debug+96>, nbytes=75) at Objects/obmalloc.c:1971
#5  0x00000000004c204e in PyObject_Malloc (size=<optimized out>) at Objects/obmalloc.c:479
#6  0x00000000004ec12f in PyUnicode_New (size=10, maxchar=<optimized out>) at Objects/unicodeobject.c:1281
#7  0x00000000005162f4 in _PyUnicodeWriter_PrepareInternal (writer=writer@entry=0x7f9971ca4cf0, length=length@entry=10, maxchar=<optimized out>, maxchar@entry=127) at Objects/unicodeobject.c:13565
#8  0x000000000051af20 in PyUnicode_DecodeUTF8Stateful (s=0x61d15b "crash_test", size=10, errors=errors@entry=0x0, consumed=consumed@entry=0x0) at Objects/unicodeobject.c:5067
#9  0x000000000051c6b0 in PyUnicode_FromString (u=<optimized out>) at Objects/unicodeobject.c:2077
#10 0x0000000000563c1c in PyImport_ImportModule (name=<optimized out>) at Python/import.c:1266
#11 0x00000000004531dd in pybind11::module::import (name=0x61d15b "crash_test") at ./pybind11/include/pybind11/pybind11.h:849
#12 0x0000000000446434 in ThreadFunc () at main.cpp:30
#13 0x000000000046a1b1 in std::_Bind_simple<void (*())()>::_M_invoke<>(std::_Index_tuple<>) (this=0x10c28d8) at /usr/include/c++/5/functional:1531
#14 0x000000000046a10a in std::_Bind_simple<void (*())()>::operator()() (this=0x10c28d8) at /usr/include/c++/5/functional:1520
#15 0x000000000046a09a in std::thread::_Impl<std::_Bind_simple<void (*())()> >::_M_run() (this=0x10c28c0) at /usr/include/c++/5/thread:115
#16 0x00007f99749e3c80 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#17 0x00007f99750bb6ba in start_thread (arg=0x7f9971ca5700) at pthread_create.c:333
#18 0x00007f997414941d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109