gh-129766: Fix crash on calling warnings._release_lock with no lock

Lib/test/test_warnings/__init__.py

@@ -1432,6 +1432,17 @@ class PyEnvironmentVariableTests(EnvironmentVariableTests, unittest.TestCase):
     module = py_warnings
 
 
+class LocksTest(unittest.TestCase):
+    @support.cpython_only
+    @unittest.skipUnless(c_warnings, 'C module is required')
+    def test_release_lock_no_lock(self):
+        with self.assertRaisesRegex(
+            RuntimeError,
+            'cannot release un-acquired lock',
+        ):
+            c_warnings._release_lock()
+
+
 class _DeprecatedTest(BaseTest, unittest.TestCase):
 
     """Test _deprecated()."""

Misc/NEWS.d/next/Library/2025-02-07-10-34-09.gh-issue-129766.6n5fQZ.rst

@@ -0,0 +1,2 @@
+Fix crash in :mod:`warnings`, when calling ``_release_lock()`` with no
+existing lock.

Python/_warnings.c

@@ -240,12 +240,12 @@ warnings_lock(PyInterpreterState *interp)
     _PyRecursiveMutex_Lock(&st->lock);
 }
 
-static inline void
+static inline int
 warnings_unlock(PyInterpreterState *interp)
 {
     WarningsState *st = warnings_get_state(interp);
     assert(st != NULL);
-    _PyRecursiveMutex_Unlock(&st->lock);
+    return _PyRecursiveMutex_TryUnlock(&st->lock);
 }
 
 static inline bool
@@ -284,7 +284,10 @@ warnings_release_lock_impl(PyObject *module)
     if (interp == NULL) {
         return NULL;
     }
-    warnings_unlock(interp);
+    if (warnings_unlock(interp) < 0) {
+        PyErr_SetString(PyExc_RuntimeError, "cannot release un-acquired lock");
+        return NULL;
+    }
     Py_RETURN_NONE;
 }