gh-116664: Make module state Py_SETREF's in _warnings thread-safe (#116959)

Mark the swap operations as critical sections.

Add an internal Py_BEGIN_CRITICAL_SECTION_MUT API that takes a PyMutex
pointer instead of a PyObject pointer.

Include/internal/pycore_critical_section.h

@@ -87,10 +87,13 @@ extern "C" {
 #define _Py_CRITICAL_SECTION_MASK           0x3
 
 #ifdef Py_GIL_DISABLED
-# define Py_BEGIN_CRITICAL_SECTION(op)                                  \
+# define Py_BEGIN_CRITICAL_SECTION_MUT(mutex)                           \
     {                                                                   \
         _PyCriticalSection _cs;                                         \
-        _PyCriticalSection_Begin(&_cs, &_PyObject_CAST(op)->ob_mutex)
+        _PyCriticalSection_Begin(&_cs, mutex)
+
+# define Py_BEGIN_CRITICAL_SECTION(op)                                  \
+        Py_BEGIN_CRITICAL_SECTION_MUT(&_PyObject_CAST(op)->ob_mutex)
 
 # define Py_END_CRITICAL_SECTION()                                      \
         _PyCriticalSection_End(&_cs);                                   \
@@ -138,6 +141,7 @@ extern "C" {
 
 #else  /* !Py_GIL_DISABLED */
 // The critical section APIs are no-ops with the GIL.
+# define Py_BEGIN_CRITICAL_SECTION_MUT(mut)
 # define Py_BEGIN_CRITICAL_SECTION(op)
 # define Py_END_CRITICAL_SECTION()
 # define Py_XBEGIN_CRITICAL_SECTION(op)

Include/internal/pycore_warnings.h

@@ -14,6 +14,7 @@ struct _warnings_runtime_state {
     PyObject *filters;  /* List */
     PyObject *once_registry;  /* Dict */
     PyObject *default_action; /* String */
+    struct _PyMutex mutex;
     long filters_version;
 };
 

Python/_warnings.c

@@ -1,4 +1,5 @@
 #include "Python.h"
+#include "pycore_critical_section.h"  // Py_BEGIN_CRITICAL_SECTION_MUT()
 #include "pycore_interp.h"        // PyInterpreterState.warnings
 #include "pycore_long.h"          // _PyLong_GetZero()
 #include "pycore_pyerrors.h"      // _PyErr_Occurred()
@@ -235,14 +236,12 @@ get_warnings_attr(PyInterpreterState *interp, PyObject *attr, int try_import)
 static PyObject *
 get_once_registry(PyInterpreterState *interp)
 {
-    PyObject *registry;
-
     WarningsState *st = warnings_get_state(interp);
-    if (st == NULL) {
+    assert(st != NULL);
-        return NULL;
-    }
 
-    registry = GET_WARNINGS_ATTR(interp, onceregistry, 0);
+    _Py_CRITICAL_SECTION_ASSERT_MUTEX_LOCKED(&st->mutex);
+
+    PyObject *registry = GET_WARNINGS_ATTR(interp, onceregistry, 0);
     if (registry == NULL) {
         if (PyErr_Occurred())
             return NULL;
@@ -265,14 +264,12 @@ get_once_registry(PyInterpreterState *interp)
 static PyObject *
 get_default_action(PyInterpreterState *interp)
 {
-    PyObject *default_action;
-
     WarningsState *st = warnings_get_state(interp);
-    if (st == NULL) {
+    assert(st != NULL);
-        return NULL;
-    }
 
-    default_action = GET_WARNINGS_ATTR(interp, defaultaction, 0);
+    _Py_CRITICAL_SECTION_ASSERT_MUTEX_LOCKED(&st->mutex);
+
+    PyObject *default_action = GET_WARNINGS_ATTR(interp, defaultaction, 0);
     if (default_action == NULL) {
         if (PyErr_Occurred()) {
             return NULL;
@@ -299,15 +296,12 @@ get_filter(PyInterpreterState *interp, PyObject *category,
            PyObject *text, Py_ssize_t lineno,
            PyObject *module, PyObject **item)
 {
-    PyObject *action;
-    Py_ssize_t i;
-    PyObject *warnings_filters;
     WarningsState *st = warnings_get_state(interp);
-    if (st == NULL) {
+    assert(st != NULL);
-        return NULL;
-    }
 
-    warnings_filters = GET_WARNINGS_ATTR(interp, filters, 0);
+    _Py_CRITICAL_SECTION_ASSERT_MUTEX_LOCKED(&st->mutex);
+
+    PyObject *warnings_filters = GET_WARNINGS_ATTR(interp, filters, 0);
     if (warnings_filters == NULL) {
         if (PyErr_Occurred())
             return NULL;
@@ -324,7 +318,7 @@ get_filter(PyInterpreterState *interp, PyObject *category,
     }
 
     /* WarningsState.filters could change while we are iterating over it. */
-    for (i = 0; i < PyList_GET_SIZE(filters); i++) {
+    for (Py_ssize_t i = 0; i < PyList_GET_SIZE(filters); i++) {
         PyObject *tmp_item, *action, *msg, *cat, *mod, *ln_obj;
         Py_ssize_t ln;
         int is_subclass, good_msg, good_mod;
@@ -384,7 +378,7 @@ get_filter(PyInterpreterState *interp, PyObject *category,
         Py_DECREF(tmp_item);
     }
 
-    action = get_default_action(interp);
+    PyObject *action = get_default_action(interp);
     if (action != NULL) {
         *item = Py_NewRef(Py_None);
         return action;
@@ -1000,8 +994,13 @@ do_warn(PyObject *message, PyObject *category, Py_ssize_t stack_level,
                        &filename, &lineno, &module, &registry))
         return NULL;
 
+    WarningsState *st = warnings_get_state(tstate->interp);
+    assert(st != NULL);
+
+    Py_BEGIN_CRITICAL_SECTION_MUT(&st->mutex);
     res = warn_explicit(tstate, category, message, filename, lineno, module, registry,
                         NULL, source);
+    Py_END_CRITICAL_SECTION();
     Py_DECREF(filename);
     Py_DECREF(registry);
     Py_DECREF(module);
@@ -1149,8 +1148,14 @@ warnings_warn_explicit_impl(PyObject *module, PyObject *message,
             return NULL;
         }
     }
+
+    WarningsState *st = warnings_get_state(tstate->interp);
+    assert(st != NULL);
+
+    Py_BEGIN_CRITICAL_SECTION_MUT(&st->mutex);
     returned = warn_explicit(tstate, category, message, filename, lineno,
                              mod, registry, source_line, sourceobj);
+    Py_END_CRITICAL_SECTION();
     Py_XDECREF(source_line);
     return returned;
 }
@@ -1290,8 +1295,14 @@ PyErr_WarnExplicitObject(PyObject *category, PyObject *message,
     if (tstate == NULL) {
         return -1;
     }
+
+    WarningsState *st = warnings_get_state(tstate->interp);
+    assert(st != NULL);
+
+    Py_BEGIN_CRITICAL_SECTION_MUT(&st->mutex);
     res = warn_explicit(tstate, category, message, filename, lineno,
                         module, registry, NULL, NULL);
+    Py_END_CRITICAL_SECTION();
     if (res == NULL)
         return -1;
     Py_DECREF(res);
@@ -1356,8 +1367,13 @@ PyErr_WarnExplicitFormat(PyObject *category,
         PyObject *res;
         PyThreadState *tstate = get_current_tstate();
         if (tstate != NULL) {
+            WarningsState *st = warnings_get_state(tstate->interp);
+            assert(st != NULL);
+
+            Py_BEGIN_CRITICAL_SECTION_MUT(&st->mutex);
             res = warn_explicit(tstate, category, message, filename, lineno,
                                 module, registry, NULL, NULL);
+            Py_END_CRITICAL_SECTION();
             Py_DECREF(message);
             if (res != NULL) {
                 Py_DECREF(res);