Canvas: Chain must properly set res.parent for chords.

celery/canvas.py

@@ -746,6 +746,7 @@ class chain(Signature):
                     task_id=prev_res.task_id, root_id=root_id, app=app,
                 )
                 prev_res = prev_prev_res
+
             if is_last_task:
                 # chain(task_id=id) means task id is set for the last task
                 # in the chain.  If the chord is part of a chord/group
@@ -769,7 +770,16 @@ class chain(Signature):
                     task.link(prev_task)
 
                 if prev_res:
-                    prev_res.parent = res
+                    if prev_res.parent:
+                        # If previous task was a chord,
+                        # the freeze above would have set a parent for
+                        # us, but we'd be overwriting it here.
+
+                        # so fix this relationship so it's:
+                        #     chord body -> group -> THIS RES
+                        prev_res.parent.parent = res
+                    else:
+                        prev_res.parent = res
 
             if is_first_task and parent_id is not None:
                 task.set_parent_id(parent_id)
@@ -1226,7 +1236,7 @@ class chord(Signature):
         if not isinstance(self.tasks, group):
             self.tasks = group(self.tasks, app=self.app)
         bodyres = self.body.freeze(_id, parent_id=self.id, root_id=root_id)
-        self.tasks.freeze(
+        bodyres.parent = self.tasks.freeze(
             parent_id=parent_id, root_id=root_id, chord=self.body)
         self.id = self.tasks.id
         self.body.set_parent_id(self.id)