gh-144763: Don't detach the GIL in tracemalloc (#144779)

tracemalloc no longer detaches the GIL to acquire its internal lock.

Co-authored-by: Kumar Aditya <kumaraditya@python.org>

diff --git a/Misc/NEWS.d/next/Library/2026-02-13-11-14-18.gh-issue-144763.cDwnEE.rst b/Misc/NEWS.d/next/Library/2026-02-13-11-14-18.gh-issue-144763.cDwnEE.rst
new file mode 100644 (file)
index 0000000..14eb4f4
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-02-13-11-14-18.gh-issue-144763.cDwnEE.rst
@@ -0,0 +1,2 @@
+Fix a race condition in :mod:`tracemalloc`: it no longer detaches the attached
+thread state to acquire its internal lock. Patch by Victor Stinner.

diff --git a/Python/tracemalloc.c b/Python/tracemalloc.c
index cdd96925d1f27a02faef667e4ed311e3d54e7135..0afc84e021817cf9b95c9ebc1e7a35a2525545c6 100644 (file)
--- a/Python/tracemalloc.c
+++ b/Python/tracemalloc.c
@@ -36,7 +36,7 @@ static int _PyTraceMalloc_TraceRef(PyObject *op, PyRefTracerEvent event,
    the GIL held from PyMem_RawFree(). It cannot acquire the lock because it
    would introduce a deadlock in _PyThreadState_DeleteCurrent(). */
 #define tables_lock _PyRuntime.tracemalloc.tables_lock
-#define TABLES_LOCK() PyMutex_Lock(&tables_lock)
+#define TABLES_LOCK() PyMutex_LockFlags(&tables_lock, _Py_LOCK_DONT_DETACH)
 #define TABLES_UNLOCK() PyMutex_Unlock(&tables_lock)
 
 
@@ -224,13 +224,20 @@ tracemalloc_get_frame(_PyInterpreterFrame *pyframe, frame_t *frame)
     assert(PyStackRef_CodeCheck(pyframe->f_executable));
     frame->filename = &_Py_STR(anon_unknown);
 
-    int lineno = PyUnstable_InterpreterFrame_GetLine(pyframe);
+    int lineno = -1;
+    PyCodeObject *code = _PyFrame_GetCode(pyframe);
+    // PyUnstable_InterpreterFrame_GetLine() cannot but used, since it uses
+    // a critical section which can trigger a deadlock.
+    int lasti = _PyFrame_SafeGetLasti(pyframe);
+    if (lasti >= 0) {
+        lineno = _PyCode_SafeAddr2Line(code, lasti);
+    }
     if (lineno < 0) {
         lineno = 0;
     }
     frame->lineno = (unsigned int)lineno;
 
-    PyObject *filename = _PyFrame_GetCode(pyframe)->co_filename;
+    PyObject *filename = code->co_filename;
     if (filename == NULL) {
 #ifdef TRACE_DEBUG
         tracemalloc_error("failed to get the filename of the code object");
@@ -863,7 +870,8 @@ _PyTraceMalloc_Stop(void)
     TABLES_LOCK();
 
     if (!tracemalloc_config.tracing) {
-        goto done;
+        TABLES_UNLOCK();
+        return;
     }
 
     /* stop tracing Python memory allocations */
@@ -880,10 +888,12 @@ _PyTraceMalloc_Stop(void)
     raw_free(tracemalloc_traceback);
     tracemalloc_traceback = NULL;
 
-    (void)PyRefTracer_SetTracer(NULL, NULL);
-
-done:
     TABLES_UNLOCK();
+
+    // Call it after TABLES_UNLOCK() since it calls _PyEval_StopTheWorldAll()
+    // which would lead to a deadlock with TABLES_LOCK() which doesn't detach
+    // the thread state.
+    (void)PyRefTracer_SetTracer(NULL, NULL);
 }