Segmentation fault at exit, copying a Python function into a static member of a C++ class

[mydatamodels]

callback_test.tar.gz

Hello there.

The purpose of this minimal test case is to save a Python function into a static member of a C++ class.

We need this because in the real project we're working on, this function will be called from a multitude of instantiated objects.
We want to avoid copying the same thing repeatedly (and also this doesn't work for us and we can't isolate a minimal case to reproduce the problem, but that's another sad story) and these objects are not accessible directly from the Python client.

If the class member is non-static everything works like a charm.

If static, execution happens as before but we get a segmentation fault exiting:

tests/test_callback.py [0.0, 1.0, 2.0, 3.0, 4.0]
[0.0, 1.0, 2.0, 3.0, 4.0]
.

=============================================================================================== 1 passed in 0.81s ===============================================================================================
--Type <RET> for more, q to quit, c to continue without paging--

Thread 1 "pytest" received signal SIGSEGV, Segmentation fault.
__GI___pthread_mutex_lock (mutex=0x1b0) at ../nptl/pthread_mutex_lock.c:67
67      ../nptl/pthread_mutex_lock.c: No such file or directory.
(gdb) where
#0  __GI___pthread_mutex_lock (mutex=0x1b0) at ../nptl/pthread_mutex_lock.c:67
#1  0x00007ffff7dab4e1 in take_gil (tstate=tstate@entry=0x55555555c550) at Python/ceval_gil.h:236
#2  0x00007ffff7dab872 in PyEval_AcquireThread (tstate=0x55555555c550) at Python/ceval.c:385
#3  0x00007fff95cae362 in ?? ()
   from /home/mvm/.pyenv/versions/3.9.7/envs/studio/lib/python3.9/site-packages/callback_test-VERSION-py3.9-linux-x86_64.egg/callback_test/_callback_test.cpython-39-x86_64-linux-gnu.so
#4  0x00007fff95cae5df in ?? ()
   from /home/mvm/.pyenv/versions/3.9.7/envs/studio/lib/python3.9/site-packages/callback_test-VERSION-py3.9-linux-x86_64.egg/callback_test/_callback_test.cpython-39-x86_64-linux-gnu.so
#5  0x00007fff95cae743 in std::_Function_base::_Base_manager<pybind11::detail::type_caster<std::function<double (std::vector<double, std::allocator<double> > const&, std::vector<double, std::allocator<double> > const&)>, void>::load(pybind11::handle, bool)::func_wrapper>::_M_manager(std::_Any_data&, std::_Any_data const&, std::_Manager_operation) ()
   from /home/mvm/.pyenv/versions/3.9.7/envs/studio/lib/python3.9/site-packages/callback_test-VERSION-py3.9-linux-x86_64.egg/callback_test/_callback_test.cpython-39-x86_64-linux-gnu.so
#6  0x00007fff95ca9a52 in ?? ()
   from /home/mvm/.pyenv/versions/3.9.7/envs/studio/lib/python3.9/site-packages/callback_test-VERSION-py3.9-linux-x86_64.egg/callback_test/_callback_test.cpython-39-x86_64-linux-gnu.so
#7  0x00007ffff7a4fa27 in __run_exit_handlers (status=status@entry=0, listp=0x7ffff7bf1718 <__exit_funcs>, run_list_atexit=run_list_atexit@entry=true, run_dtors=run_dtors@entry=true) at exit.c:108
#8  0x00007ffff7a4fbe0 in __GI_exit (status=status@entry=0) at exit.c:139
#9  0x00007ffff7debc0d in Py_Exit (sts=0) at Python/pylifecycle.c:2437
#10 0x00007ffff7df046f in handle_system_exit () at Python/pythonrun.c:722
#11 _PyErr_PrintEx (tstate=0x55555555c550, set_sys_last_vars=set_sys_last_vars@entry=1) at Python/pythonrun.c:779
#12 0x00007ffff7df04a9 in PyErr_PrintEx (set_sys_last_vars=set_sys_last_vars@entry=1) at Python/pythonrun.c:827
#13 0x00007ffff7df04be in PyErr_Print () at Python/pythonrun.c:833
#14 0x00007ffff7df1a73 in pyrun_simple_file (flags=<optimized out>, closeit=1, filename=0x7ffff73d3030, fp=0x555555559340) at Python/pythonrun.c:455
#15 PyRun_SimpleFileExFlags (fp=fp@entry=0x555555559340, filename=<optimized out>, closeit=closeit@entry=1, flags=flags@entry=0x7fffffffdac8) at Python/pythonrun.c:482
#16 0x00007ffff7df1d1c in PyRun_AnyFileExFlags (fp=fp@entry=0x555555559340, filename=<optimized out>, closeit=closeit@entry=1, flags=flags@entry=0x7fffffffdac8) at Python/pythonrun.c:91
#17 0x00007ffff7e10048 in pymain_run_file (cf=0x7fffffffdac8, config=0x55555555d8a0) at Modules/main.c:373
#18 pymain_run_python (exitcode=0x7fffffffdabc) at Modules/main.c:598
#19 Py_RunMain () at Modules/main.c:677
#20 0x00007ffff7e104ea in pymain_main (args=0x7fffffffdbc0) at Modules/main.c:707
#21 Py_BytesMain (argc=<optimized out>, argv=<optimized out>) at Modules/main.c:731
#22 0x00007ffff7a2d0b3 in __libc_start_main (main=0x555555555060 <main>, argc=4, argv=0x7fffffffdd28, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7fffffffdd18)
    at ../csu/libc-start.c:308
#23 0x000055555555509e in _start ()

Can someone tell me what's wrong with copying the function into a static member, please?

pybind11 v2.8.1
gcc 9.3.0
python 3.9.7