Guard against core dump from uninitialized subplan.

tglsfdc · tglsfdc · commit 55416b26a98f · 2020-11-03T16:16:36.000-05:00
If the planner erroneously puts a non-parallel-safe SubPlan into a parallelized portion of the query tree, nodeSubplan.c will fail in the worker processes because it finds a null in es_subplanstates, which it's unable to cope with. It seems worth a test-and-elog to make that an error case rather than a core dump case. This probably should have been included in commit 16ebab6, which was responsible for allowing nulls to appear in es_subplanstates to begin with. So, back-patch to v10 where that came in. Discussion: https://postgr.es/m/924226.1604422326@sss.pgh.pa.us
diff --git a/src/backend/executor/nodeSubplan.c b/src/backend/executor/nodeSubplan.c
@@ -798,7 +798,15 @@ ExecInitSubPlan(SubPlan *subplan, PlanState *parent)
 	sstate->planstate = (PlanState *) list_nth(estate->es_subplanstates,
 											   subplan->plan_id - 1);
 
-	/* ... and to its parent's state */
+	/*
+	 * This check can fail if the planner mistakenly puts a parallel-unsafe
+	 * subplan into a parallelized subquery; see ExecSerializePlan.
+	 */
+	if (sstate->planstate == NULL)
+		elog(ERROR, "subplan \"%s\" was not initialized",
+			 subplan->plan_name);
+
+	/* Link to parent's state, too */
 	sstate->parent = parent;
 
 	/* Initialize subexpressions */
