gh-155725: Remove PyGILState_Ensure usage from tracemalloc

Include/internal/pycore_tracemalloc.h

@@ -44,9 +44,10 @@ struct
 __attribute__((packed))
 #endif
 tracemalloc_frame {
-    /* filename cannot be NULL: "<unknown>" is used if the Python frame
-       filename is NULL */
-    PyObject *filename;
+    /* Interned NUL terminated UTF-8 (surrogatepass) string.
+       Cannot be NULL: "<unknown>" is used if the Python frame filename
+       cannot be captured. */
+    const char *filename;
     unsigned int lineno;
 };
 
@@ -85,7 +86,7 @@ struct _tracemalloc_runtime_state {
        Protected by TABLES_LOCK(). */
     size_t peak_traced_memory;
     /* Hash table used as a set to intern filenames:
-       PyObject* => PyObject*.
+       char* (NUL terminated UTF-8 string) => NULL.
        Protected by the TABLES_LOCK(). */
     _Py_hashtable_t *filenames;
     /* Buffer to store a new traceback in traceback_new().

Lib/test/test_tracemalloc.py

@@ -1056,8 +1056,8 @@ def test_track(self):
         self.check_track(False)
 
     def test_track_without_gil(self):
-        # check that calling _PyTraceMalloc_Track() without holding the GIL
-        # works too
+        # check that calling PyTraceMalloc_Track() without the GIL
+        # (detached thread state) still captures the Python traceback
         self.check_track(True)
 
     def test_track_already_tracked(self):

Misc/NEWS.d/next/Core_and_Builtins/2026-08-26-10-00-00.gh-issue-155725.tRcMal.rst

@@ -0,0 +1,6 @@
+:mod:`tracemalloc` no longer acquires the :term:`GIL` nor creates a
+temporary thread state to trace memory allocations: traceback frames now
+store plain UTF-8 strings instead of Python str objects, and tracebacks are
+captured using the Python thread state already associated with the calling
+thread, even if it is not attached. Threads without a Python thread state
+record the traceback as ``<unknown>``.