I can reproduce PyOS_InterruptOccurred() crash in Python 3.8 if I remove readline.cpython-38d-x86_64-linux-gnu.so and I disable EINTR error checking in my_fgets():

diff --git a/Parser/myreadline.c b/Parser/myreadline.c
index 43e5583b8b..2712dedacd 100644
--- a/Parser/myreadline.c
+++ b/Parser/myreadline.c
@@ -73,7 +73,7 @@ my_fgets(char *buf, int len, FILE *fp)
             clearerr(fp);
             return -1; /* EOF */
         }
-#ifdef EINTR
+#if 0
         if (err == EINTR) {
             int s;
             PyEval_RestoreThread(_PyOS_ReadlineTState);


vstinner@apu$ ./python
Python 3.8.3+ (heads/3.8-dirty:00a240bf7f, Jun  1 2020, 17:00:22) 
[GCC 10.1.1 20200507 (Red Hat 10.1.1-1)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> 
^C
Erreur de segmentation (core dumped)


I cannot reproduce the issue in Python 3.7.

---

Python 3.7:
---
int
PyOS_InterruptOccurred(void)
{
    if (_Py_atomic_load_relaxed(&Handlers[SIGINT].tripped)) {
        if (PyThread_get_thread_ident() != main_thread)
            return 0;
        _Py_atomic_store_relaxed(&Handlers[SIGINT].tripped, 0);
        return 1;
    }
    return 0;
}
---

Python 3.8:
---
static int
is_main(_PyRuntimeState *runtime)
{
    unsigned long thread = PyThread_get_thread_ident();
    PyInterpreterState *interp = _PyRuntimeState_GetThreadState(runtime)->interp;
    return (thread == runtime->main_thread
            && interp == runtime->interpreters.main);
}

int
PyOS_InterruptOccurred(void)
{
    if (_Py_atomic_load_relaxed(&Handlers[SIGINT].tripped)) {
        _PyRuntimeState *runtime = &_PyRuntime;
        if (!is_main(runtime)) {
            return 0;
        }
        _Py_atomic_store_relaxed(&Handlers[SIGINT].tripped, 0);
        return 1;
    }
    return 0;
}
---

is_main() function was added in Python 3.8 by:

commit 64d6cc826dacebc2493b1bb5e8cb97828eb76f81
Author: Eric Snow <ericsnowcurrently@gmail.com>
Date:   Sat Feb 23 15:40:43 2019 -0700

    bpo-35724: Explicitly require the main interpreter for signal-handling. (GH-11530)
    
    Ensure that the main interpreter is active (in the main thread) for signal-handling operations. This is increasingly relevant as people use subinterpreters more.
    
    https://bugs.python.org/issue35724