pythongh-128679: Fix tracemalloc.stop() race conditions (python#128893)

tracemalloc_alloc(), tracemalloc_realloc(), tracemalloc_free(),
_PyTraceMalloc_TraceRef() and _PyTraceMalloc_GetMemory() now check
'tracemalloc_config.tracing' after calling TABLES_LOCK().

_PyTraceMalloc_TraceRef() now always returns 0.

Author: vstinner

Lib/test/test_tracemalloc.py

@@ -7,8 +7,9 @@
 from test.support.script_helper import (assert_python_ok, assert_python_failure,
                                         interpreter_requires_environment)
 from test import support
-from test.support import os_helper
 from test.support import force_not_colorized
+from test.support import os_helper
+from test.support import threading_helper
 
 try:
     import _testcapi
@@ -952,7 +953,6 @@ def check_env_var_invalid(self, nframe):
             return
         self.fail(f"unexpected output: {stderr!a}")
 
-
     def test_env_var_invalid(self):
         for nframe in INVALID_NFRAME:
             with self.subTest(nframe=nframe):
@@ -1101,6 +1101,12 @@ def test_stop_untrack(self):
         with self.assertRaises(RuntimeError):
             self.untrack()
 
+    @unittest.skipIf(_testcapi is None, 'need _testcapi')
+    @threading_helper.requires_working_threading()
+    def test_tracemalloc_track_race(self):
+        # gh-128679: Test fix for tracemalloc.stop() race condition
+        _testcapi.tracemalloc_track_race()
+
 
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS.d/next/Library/2025-01-15-21-41-51.gh-issue-128679.tq10F2.rst

@@ -0,0 +1,3 @@
+:mod:`tracemalloc`: Fix race conditions when :func:`tracemalloc.stop` is
+called by a thread, while other threads are tracing memory allocations.
+Patch by Victor Stinner.

Modules/_testcapimodule.c

@@ -3435,6 +3435,104 @@ code_offset_to_line(PyObject* self, PyObject* const* args, Py_ssize_t nargsf)
     return PyLong_FromInt32(PyCode_Addr2Line(code, offset));
 }
 
+
+static void
+tracemalloc_track_race_thread(void *data)
+{
+    PyTraceMalloc_Track(123, 10, 1);
+
+    PyThread_type_lock lock = (PyThread_type_lock)data;
+    PyThread_release_lock(lock);
+}
+
+// gh-128679: Test fix for tracemalloc.stop() race condition
+static PyObject *
+tracemalloc_track_race(PyObject *self, PyObject *args)
+{
+#define NTHREAD 50
+    PyObject *tracemalloc = NULL;
+    PyObject *stop = NULL;
+    PyThread_type_lock locks[NTHREAD];
+    memset(locks, 0, sizeof(locks));
+
+    // Call tracemalloc.start()
+    tracemalloc = PyImport_ImportModule("tracemalloc");
+    if (tracemalloc == NULL) {
+        goto error;
+    }
+    PyObject *start = PyObject_GetAttrString(tracemalloc, "start");
+    if (start == NULL) {
+        goto error;
+    }
+    PyObject *res = PyObject_CallNoArgs(start);
+    Py_DECREF(start);
+    if (res == NULL) {
+        goto error;
+    }
+    Py_DECREF(res);
+
+    stop = PyObject_GetAttrString(tracemalloc, "stop");
+    Py_CLEAR(tracemalloc);
+    if (stop == NULL) {
+        goto error;
+    }
+
+    // Start threads
+    for (size_t i = 0; i < NTHREAD; i++) {
+        PyThread_type_lock lock = PyThread_allocate_lock();
+        if (!lock) {
+            PyErr_NoMemory();
+            goto error;
+        }
+        locks[i] = lock;
+        PyThread_acquire_lock(lock, 1);
+
+        unsigned long thread;
+        thread = PyThread_start_new_thread(tracemalloc_track_race_thread,
+                                           (void*)lock);
+        if (thread == (unsigned long)-1) {
+            PyErr_SetString(PyExc_RuntimeError, "can't start new thread");
+            goto error;
+        }
+    }
+
+    // Call tracemalloc.stop() while threads are running
+    res = PyObject_CallNoArgs(stop);
+    Py_CLEAR(stop);
+    if (res == NULL) {
+        goto error;
+    }
+    Py_DECREF(res);
+
+    // Wait until threads complete with the GIL released
+    Py_BEGIN_ALLOW_THREADS
+    for (size_t i = 0; i < NTHREAD; i++) {
+        PyThread_type_lock lock = locks[i];
+        PyThread_acquire_lock(lock, 1);
+        PyThread_release_lock(lock);
+    }
+    Py_END_ALLOW_THREADS
+
+    // Free threads locks
+    for (size_t i=0; i < NTHREAD; i++) {
+        PyThread_type_lock lock = locks[i];
+        PyThread_free_lock(lock);
+    }
+    Py_RETURN_NONE;
+
+error:
+    Py_CLEAR(tracemalloc);
+    Py_CLEAR(stop);
+    for (size_t i=0; i < NTHREAD; i++) {
+        PyThread_type_lock lock = locks[i];
+        if (lock) {
+            PyThread_free_lock(lock);
+        }
+    }
+    return NULL;
+#undef NTHREAD
+}
+
 static PyMethodDef TestMethods[] = {
     {"set_errno",               set_errno,                       METH_VARARGS},
     {"test_config",             test_config,                     METH_NOARGS},
@@ -3578,6 +3676,7 @@ static PyMethodDef TestMethods[] = {
     {"type_freeze", type_freeze, METH_VARARGS},
     {"test_atexit", test_atexit, METH_NOARGS},
     {"code_offset_to_line", _PyCFunction_CAST(code_offset_to_line), METH_FASTCALL},
+    {"tracemalloc_track_race", tracemalloc_track_race, METH_NOARGS},
     {NULL, NULL} /* sentinel */
 };
 

Python/tracemalloc.c

@@ -567,11 +567,14 @@ tracemalloc_alloc(int need_gil, int use_calloc,
     }
     TABLES_LOCK();
 
-    if (ADD_TRACE(ptr, nelem * elsize) < 0) {
-        // Failed to allocate a trace for the new memory block
-        alloc->free(alloc->ctx, ptr);
-        ptr = NULL;
+    if (tracemalloc_config.tracing) {
+        if (ADD_TRACE(ptr, nelem * elsize) < 0) {
+            // Failed to allocate a trace for the new memory block
+            alloc->free(alloc->ctx, ptr);
+            ptr = NULL;
+        }
     }
+    // else: gh-128679: tracemalloc.stop() was called by another thread
 
     TABLES_UNLOCK();
     if (need_gil) {
@@ -614,6 +617,11 @@ tracemalloc_realloc(int need_gil, void *ctx, void *ptr, size_t new_size)
     }
     TABLES_LOCK();
 
+    if (!tracemalloc_config.tracing) {
+        // gh-128679: tracemalloc.stop() was called by another thread
+        goto unlock;
+    }
+
     if (ptr != NULL) {
         // An existing memory block has been resized
 
@@ -646,6 +654,7 @@ tracemalloc_realloc(int need_gil, void *ctx, void *ptr, size_t new_size)
         }
     }
 
+unlock:
     TABLES_UNLOCK();
     if (need_gil) {
         PyGILState_Release(gil_state);
@@ -674,7 +683,12 @@ tracemalloc_free(void *ctx, void *ptr)
     }
 
     TABLES_LOCK();
-    REMOVE_TRACE(ptr);
+
+    if (tracemalloc_config.tracing) {
+        REMOVE_TRACE(ptr);
+    }
+    // else: gh-128679: tracemalloc.stop() was called by another thread
+
     TABLES_UNLOCK();
 }
 
@@ -1312,8 +1326,9 @@ _PyTraceMalloc_TraceRef(PyObject *op, PyRefTracerEvent event,
     assert(PyGILState_Check());
     TABLES_LOCK();
 
-    int result = -1;
-    assert(tracemalloc_config.tracing);
+    if (!tracemalloc_config.tracing) {
+        goto done;
+    }
 
     PyTypeObject *type = Py_TYPE(op);
     const size_t presize = _PyType_PreHeaderSize(type);
@@ -1325,13 +1340,13 @@ _PyTraceMalloc_TraceRef(PyObject *op, PyRefTracerEvent event,
         traceback_t *traceback = traceback_new();
         if (traceback != NULL) {
             trace->traceback = traceback;
-            result = 0;
         }
     }
     /* else: cannot track the object, its memory block size is unknown */
 
+done:
     TABLES_UNLOCK();
-    return result;
+    return 0;
 }
 
 
@@ -1472,13 +1487,19 @@ int _PyTraceMalloc_GetTracebackLimit(void)
 size_t
 _PyTraceMalloc_GetMemory(void)
 {
-    size_t size = _Py_hashtable_size(tracemalloc_tracebacks);
-    size += _Py_hashtable_size(tracemalloc_filenames);
-
     TABLES_LOCK();
-    size += _Py_hashtable_size(tracemalloc_traces);
-    _Py_hashtable_foreach(tracemalloc_domains,
-                          tracemalloc_get_tracemalloc_memory_cb, &size);
+    size_t size;
+    if (tracemalloc_config.tracing) {
+        size = _Py_hashtable_size(tracemalloc_tracebacks);
+        size += _Py_hashtable_size(tracemalloc_filenames);
+
+        size += _Py_hashtable_size(tracemalloc_traces);
+        _Py_hashtable_foreach(tracemalloc_domains,
+                              tracemalloc_get_tracemalloc_memory_cb, &size);
+    }
+    else {
+        size = 0;
+    }
     TABLES_UNLOCK();
     return size;
 }