Fix tupdesc dangling pointer segfault in HashAgg

This problem manifests itself with HashAgg on the top of
DynamicIndexScan node and can cause a segmentation fault.

1. A HashAgg node initializes a tuple descriptor for its hash
slot using a reference from input tuples (coming from
DynamicIndexScan through a Sequence node).
2. At the end of every partition index scan in DynamicIndexScan
we unlink and free unused memory chunks and reset partition's
memory context. It causes a total destruction of all objects in
the context including partition index tuple descriptor used in a
HashAgg node.
As a result we get a dangling pointer in HashAgg on switching to
a new index partition during DynamicIndexScan that can cause a
segfault.

src/backend/executor/execHHashagg.c

@@ -931,6 +931,7 @@ agg_hash_initial_pass(AggState *aggstate)
 		HashKey hashkey;
 		bool isNew;
 		HashAggEntry *entry;
+		TupleDesc slot_desc;
 
 		/* no more tuple. Done */
 		if (TupIsNull(outerslot))
@@ -943,8 +944,16 @@ agg_hash_initial_pass(AggState *aggstate)
 		{
 			int size;
 							
-			/* Initialize hashslot by cloning input slot. */
-			ExecSetSlotDescriptor(aggstate->hashslot, outerslot->tts_tupleDescriptor); 
+			/*
+			 * Initialize hashslot with a copy of an input slot.
+			 * We should not use slot's tuple descriptor reference
+			 * because DynamicXXX scan memory contexts are resetted
+			 * at the end of every partition scan (that can cause
+			 * dangling pointers).
+			 */
+			slot_desc = CreateTupleDescCopy(outerslot->tts_tupleDescriptor);
+
+			ExecSetSlotDescriptor(aggstate->hashslot, slot_desc);
 			ExecStoreAllNullTuple(aggstate->hashslot);
 
 			size = ((Agg *)aggstate->ss.ps.plan)->numCols * sizeof(HashKey);

src/test/regress/expected/partition.out

@@ -4127,6 +4127,36 @@ select * from pg_indexes where schemaname = 'public' and tablename like 'ti%';
 (0 rows)
 
 drop table ti;
+-- Partitioned table with btree index and hash aggregate should use a correct
+-- memory context for its tuples` descriptor
+drop table if exists dis_tupdesc;
+NOTICE:  table "dis_tupdesc" does not exist, skipping
+create table dis_tupdesc (a int, b int, c int)
+distributed by (a)
+partition by list (b)
+(
+    partition p1 values (1),
+    partition p2 values (2),
+    default partition junk_data
+);
+NOTICE:  CREATE TABLE will create partition "dis_tupdesc_1_prt_p1" for table "dis_tupdesc"
+NOTICE:  CREATE TABLE will create partition "dis_tupdesc_1_prt_p2" for table "dis_tupdesc"
+NOTICE:  CREATE TABLE will create partition "dis_tupdesc_1_prt_junk_data" for table "dis_tupdesc"
+create index dis_tupdesc_idx on dis_tupdesc using btree (c);
+insert into dis_tupdesc select i, i % 3, i % 4 from generate_series (1, 240) as i;
+analyze dis_tupdesc;
+set gp_segments_for_planner = 2;
+set optimizer_segments = 2;
+select distinct b from dis_tupdesc where c >= 2;
+ b 
+---
+ 0
+ 1
+ 2
+(3 rows)
+
+reset gp_segments_for_planner;
+reset optimizer_segments;
 -- MPP-6611, make sure rename works with default partitions
 create table it (i int, j int) partition by range(i) 
 subpartition by range(j) subpartition template(start(1) end(10) every(5))

src/test/regress/expected/partition_optimizer.out

@@ -4140,6 +4140,36 @@ select * from pg_indexes where schemaname = 'public' and tablename like 'ti%';
 (0 rows)
 
 drop table ti;
+-- Partitioned table with btree index and hash aggregate should use a correct
+-- memory context for its tuples` descriptor
+drop table if exists dis_tupdesc;
+NOTICE:  table "dis_tupdesc" does not exist, skipping
+create table dis_tupdesc (a int, b int, c int)
+distributed by (a)
+partition by list (b)
+(
+    partition p1 values (1),
+    partition p2 values (2),
+    default partition junk_data
+);
+NOTICE:  CREATE TABLE will create partition "dis_tupdesc_1_prt_p1" for table "dis_tupdesc"
+NOTICE:  CREATE TABLE will create partition "dis_tupdesc_1_prt_p2" for table "dis_tupdesc"
+NOTICE:  CREATE TABLE will create partition "dis_tupdesc_1_prt_junk_data" for table "dis_tupdesc"
+create index dis_tupdesc_idx on dis_tupdesc using btree (c);
+insert into dis_tupdesc select i, i % 3, i % 4 from generate_series (1, 240) as i;
+analyze dis_tupdesc;
+set gp_segments_for_planner = 2;
+set optimizer_segments = 2;
+select distinct b from dis_tupdesc where c >= 2;
+ b 
+---
+ 0
+ 1
+ 2
+(3 rows)
+
+reset gp_segments_for_planner;
+reset optimizer_segments;
 -- MPP-6611, make sure rename works with default partitions
 create table it (i int, j int) partition by range(i) 
 subpartition by range(j) subpartition template(start(1) end(10) every(5))

src/test/regress/sql/partition.sql

@@ -2138,6 +2138,26 @@ drop index ti_j_idx;
 select * from pg_indexes where schemaname = 'public' and tablename like 'ti%';
 drop table ti;
 
+-- Partitioned table with btree index and hash aggregate should use a correct
+-- memory context for its tuples` descriptor
+drop table if exists dis_tupdesc;
+create table dis_tupdesc (a int, b int, c int)
+distributed by (a)
+partition by list (b)
+(
+    partition p1 values (1),
+    partition p2 values (2),
+    default partition junk_data
+);
+create index dis_tupdesc_idx on dis_tupdesc using btree (c);
+insert into dis_tupdesc select i, i % 3, i % 4 from generate_series (1, 240) as i;
+analyze dis_tupdesc;
+set gp_segments_for_planner = 2;
+set optimizer_segments = 2;
+select distinct b from dis_tupdesc where c >= 2;
+reset gp_segments_for_planner;
+reset optimizer_segments;
+
 -- MPP-6611, make sure rename works with default partitions
 create table it (i int, j int) partition by range(i) 
 subpartition by range(j) subpartition template(start(1) end(10) every(5))