GH-102397: Fix segfault from race condition in signal handling (#102399)

Co-authored-by: Gregory P. Smith <greg@krypto.org>

Lib/test/test_signal.py

@@ -1406,6 +1406,21 @@ def handler(a, b):
         signal.raise_signal(signal.SIGINT)
         self.assertTrue(is_ok)
 
+    def test__thread_interrupt_main(self):
+        # See https://github.com/python/cpython/issues/102397
+        code = """if 1:
+        import _thread
+        class Foo():
+            def __del__(self):
+                _thread.interrupt_main()
+
+        x = Foo()
+        """
+
+        rc, out, err = assert_python_ok('-c', code)
+        self.assertIn(b'OSError: Signal 2 ignored due to race condition', err)
+
+
 
 class PidfdSignalTest(unittest.TestCase):
 

Misc/NEWS.d/next/Core and Builtins/2023-03-04-06-48-34.gh-issue-102397.ACJaOf.rst

@@ -0,0 +1,2 @@
+Fix segfault from race condition in signal handling during garbage collection.
+Patch by Kumar Aditya.

Modules/signalmodule.c

@@ -148,6 +148,10 @@ get_signal_state(PyObject *module)
 static inline int
 compare_handler(PyObject *func, PyObject *dfl_ign_handler)
 {
+    // See https://github.com/python/cpython/pull/102399
+    if (func == NULL || dfl_ign_handler == NULL) {
+        return 0;
+    }
     assert(PyLong_CheckExact(dfl_ign_handler));
     if (!PyLong_CheckExact(func)) {
         return 0;