pythongh-92036: Fix gc_fini_untrack() (pythonGH-92037)

Fix a crash in subinterpreters related to the garbage collector. When a subinterpreter is deleted, untrack all objects tracked by its GC. To prevent a crash in deallocator functions expecting objects to be tracked by the GC, leak a strong reference to these objects on purpose, so they are never deleted and their deallocator functions are not called. (cherry picked from commit 1424336) Co-authored-by: Victor Stinner <[email protected]>
hello-adam · Jun 2, 2022 · ede522e · ede522e
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diff --git a/Misc/NEWS.d/next/Core and Builtins/2022-04-28-23-37-30.gh-issue-92036.GZJAC9.rst b/Misc/NEWS.d/next/Core and Builtins/2022-04-28-23-37-30.gh-issue-92036.GZJAC9.rst
@@ -0,0 +1,5 @@
+Fix a crash in subinterpreters related to the garbage collector. When a
+subinterpreter is deleted, untrack all objects tracked by its GC. To prevent a
+crash in deallocator functions expecting objects to be tracked by the GC, leak
+a strong reference to these objects on purpose, so they are never deleted and
+their deallocator functions are not called. Patch by Victor Stinner.
diff --git a/Modules/gcmodule.c b/Modules/gcmodule.c
@@ -2157,6 +2157,12 @@ gc_fini_untrack(PyGC_Head *list)
     for (gc = GC_NEXT(list); gc != list; gc = GC_NEXT(list)) {
         PyObject *op = FROM_GC(gc);
         _PyObject_GC_UNTRACK(op);
+        // gh-92036: If a deallocator function expect the object to be tracked
+        // by the GC (ex: func_dealloc()), it can crash if called on an object
+        // which is no longer tracked by the GC. Leak one strong reference on
+        // purpose so the object is never deleted and its deallocator is not
+        // called.
+        Py_INCREF(op);
     }
 }