Fix a subtle bug in the trashcan code I added yesterday to

subtype_dealloc().

When call_finalizer() failed, it would return without going through
the trashcan end macro, thereby unbalancing the trashcan nesting level
counter, and thereby defeating the test case (slottrash() in
test_descr.py).  This in turn meant that the assert in the GC_UNTRACK
macro wasn't triggered by the slottrash() test despite a bug in the
code: _PyTrash_destroy_chain() calls the dealloc routine with an
object that's untracked, and the assert in the GC_UNTRACK macro would
fail on this; but because of an earlier test that resurrects an
object, causing call_finalizer() to fail and the trashcan nesting
level to be unbalanced, so _PyTrash_destroy_chain() was never called.
Calling the slottrash() test in isolation *did* trigger the assert,
however.

So the fix is twofold: (1) call the GC_UnTrack() function instead of
the GC_UNTRACK macro, because the function is safe when the object is
already untracked; (2) when call_finalizer() fails, jump to a label
that exits through the trashcan end macro, keeping the trashcan
nesting balanced.

1 files changed, 3 insertions, 2 deletions

diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index b7edb14..d494344 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -463,13 +463,13 @@ subtype_dealloc(PyObject *self)
 	/* We get here only if the type has GC */
 
 	/* UnTrack and re-Track around the trashcan macro, alas */
-	_PyObject_GC_UNTRACK(self);
+	PyObject_GC_UnTrack(self);
 	Py_TRASHCAN_SAFE_BEGIN(self);
 	_PyObject_GC_TRACK(self); /* We'll untrack for real later */
 
 	/* Maybe call finalizer; exit early if resurrected */
 	if (call_finalizer(self) < 0)
-		return;
+		goto endlabel;
 
 	/* Find the nearest base with a different tp_dealloc
 	   and clear slots while we're at it */
@@ -508,6 +508,7 @@ subtype_dealloc(PyObject *self)
 	/* Can't reference self beyond this point */
 	Py_DECREF(type);
 
+  endlabel:
 	Py_TRASHCAN_SAFE_END(self);
 }