OCaml Gc caused Fatal Python Error: Python memory allocator called without holding the GIL

[tysg]

First of all, thank you for the amazing package! We had this error, detailed below:

Error output:

Fatal Python error: _PyMem_DebugFree: Python memory allocator called without holding the GIL
Python runtime state: initialized

Thread 0x00007f5261293180 (most recent call first):
<no Python frame>

gdb backtrace:

(gdb) bt
#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
#1  0x00007f52621d8537 in __GI_abort () at abort.c:79
#2  0x00007f525991df5f in fatal_error_exit (status=<optimized out>) at ../Python/pylifecycle.c:2201
#3  0x00007f525991eff9 in fatal_error (stream=<optimized out>, header=header@entry=1, prefix=prefix@entry=0x7f5259a780d0 <__func__.13> "_PyMem_DebugFree", msg=msg@entry=0x7f5259a77a00 "Python memory allocator called without holding the GIL", status=status@entry=-1) at ../Python/pylifecycle.c:2285
#4  0x00007f52599217cb in _Py_FatalErrorFunc (func=func@entry=0x7f5259a780d0 <__func__.13> "_PyMem_DebugFree", msg=msg@entry=0x7f5259a77a00 "Python memory allocator called without holding the GIL") at ../Python/pylifecycle.c:2301
#5  0x00007f525981f7e9 in _PyMem_DebugCheckGIL (func=0x7f5259a780d0 <__func__.13> "_PyMem_DebugFree") at ../Objects/obmalloc.c:2320
#6  _PyMem_DebugFree (ctx=0x7f5259cd3ad0 <_PyMem_Debug+48>, ptr=0x7f4ff8178400) at ../Objects/obmalloc.c:2344
#7  0x00007f52598203cf in PyMem_Free (ptr=<optimized out>) at ../Objects/obmalloc.c:629
#8  0x00007f52597ef403 in list_dealloc (op=0x7f4ff816c640) at ../Objects/listobject.c:338
#9  0x000055c72a0fafbe in caml_empty_minor_heap () at minor_gc.c:413
#10 0x000055c72a0fb438 in caml_gc_dispatch () at minor_gc.c:492
#11 0x000055c72a0fb556 in caml_alloc_small_dispatch (wosize=6, flags=3, nallocs=2, encoded_alloc_lens=0x55c72d8ad9d1 <camlCtypes_ptr__frametable+49> "\002\001") at minor_gc.c:539
#12 0x000055c72a115dca in caml_call_gc ()
#13 0x000055c72976f084 in camlCtypes_ptr__add_bytes_391 () at src/ctypes/ctypes_ptr.ml:76
#14 0x000055c72977478b in camlCtypes_memory__$2b$40_742 () at src/ctypes/ctypes_memory.ml:114
#15 0x000055c72964e0f9 in camlOnnx__Wrappers__fun_3581 () at src/ctypes/ctypes_memory.ml:175
#16 0x000055c729b63f23 in camlBase__Array0__init_1279 () at src/array0.ml:88
#17 0x000055c729f59e39 in camlLwt_preemptive__task_819 () at src/unix/lwt_preemptive.ml:184
#18 0x000055c729f59988 in camlLwt_preemptive__worker_loop_534 () at src/unix/lwt_preemptive.ml:104
#19 0x000055c729f857b5 in camlThread__fun_850 () at thread.ml:49
#20 0x000055c72a115f01 in caml_start_program ()
#21 0x000055c72a10c97d in caml_callback_exn (closure=closure@entry=139991788601392, arg=<optimized out>, arg@entry=1) at callback.c:111
#22 0x000055c72a0edcc0 in caml_thread_start (arg=0x55c735c81280) at st_stubs.c:548
#23 0x00007f5262886ea7 in start_thread (arg=<optimized out>) at pthread_create.c:477
#24 0x00007f52622b1a2f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

From what I can see, OCaml Gc tried to reclaim memory holding by Python, without holding the GIL. Unfortunately I cannot provide a minimal reproduction, but I can continue to monitor this and report more findings if I have them.