Fix freeing a child join's SpecialJoinInfo

In try_partitionwise_join, we try to break down the join between two
partitioned relations into joins between matching partitions.  To
achieve this, we iterate through each pair of partitions from the two
joining relations and create child join relations for them.  To reduce
memory accumulation during each iteration, one step we take is freeing
the SpecialJoinInfos created for the child joins.

A child join's SpecialJoinInfo is a copy of the parent join's
SpecialJoinInfo, with some members being translated copies of their
counterparts in the parent.  However, when freeing the bitmapset
members in a child join's SpecialJoinInfo, we failed to check whether
they were translated copies.  As a result, we inadvertently freed the
members that were still in use by the parent SpecialJoinInfo, leading
to crashes when those freed members were accessed.

To fix, check if each member of the child join's SpecialJoinInfo is a
translated copy and free it only if that's the case.  This requires
passing the parent join's SpecialJoinInfo as a parameter to
free_child_join_sjinfo.

Back-patch to v17 where this bug crept in.

Bug: #18806
Reported-by: 孟令彬 <m_lingbin@126.com>
Diagnosed-by: Tender Wang <tndrwang@gmail.com>
Author: Richard Guo <guofenglinux@gmail.com>
Reviewed-by: Amit Langote <amitlangote09@gmail.com>
Reviewed-by: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Discussion: https://postgr.es/m/18806-d70b0c9fdf63dcbf@postgresql.org
Backpatch-through: 17

1 files changed, 25 insertions, 9 deletions

diff --git a/src/backend/optimizer/path/joinrels.c b/src/backend/optimizer/path/joinrels.c
index c2eb300ea9b..60d65762b5d 100644
--- a/src/backend/optimizer/path/joinrels.c
+++ b/src/backend/optimizer/path/joinrels.c
@@ -45,7 +45,8 @@ static void try_partitionwise_join(PlannerInfo *root, RelOptInfo *rel1,
 static SpecialJoinInfo *build_child_join_sjinfo(PlannerInfo *root,
 												SpecialJoinInfo *parent_sjinfo,
 												Relids left_relids, Relids right_relids);
-static void free_child_join_sjinfo(SpecialJoinInfo *sjinfo);
+static void free_child_join_sjinfo(SpecialJoinInfo *child_sjinfo,
+								   SpecialJoinInfo *parent_sjinfo);
 static void compute_partition_bounds(PlannerInfo *root, RelOptInfo *rel1,
 									 RelOptInfo *rel2, RelOptInfo *joinrel,
 									 SpecialJoinInfo *parent_sjinfo,
@@ -1687,7 +1688,7 @@ try_partitionwise_join(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
 		 */
 		pfree(appinfos);
 		bms_free(child_relids);
-		free_child_join_sjinfo(child_sjinfo);
+		free_child_join_sjinfo(child_sjinfo, parent_sjinfo);
 	}
 }
 
@@ -1754,18 +1755,33 @@ build_child_join_sjinfo(PlannerInfo *root, SpecialJoinInfo *parent_sjinfo,
  * SpecialJoinInfo are freed here.
  */
 static void
-free_child_join_sjinfo(SpecialJoinInfo *sjinfo)
+free_child_join_sjinfo(SpecialJoinInfo *child_sjinfo,
+					   SpecialJoinInfo *parent_sjinfo)
 {
 	/*
 	 * Dummy SpecialJoinInfos of inner joins do not have any translated fields
 	 * and hence no fields that to be freed.
 	 */
-	if (sjinfo->jointype != JOIN_INNER)
+	if (child_sjinfo->jointype != JOIN_INNER)
 	{
-		bms_free(sjinfo->min_lefthand);
-		bms_free(sjinfo->min_righthand);
-		bms_free(sjinfo->syn_lefthand);
-		bms_free(sjinfo->syn_righthand);
+		if (child_sjinfo->min_lefthand != parent_sjinfo->min_lefthand)
+			bms_free(child_sjinfo->min_lefthand);
+
+		if (child_sjinfo->min_righthand != parent_sjinfo->min_righthand)
+			bms_free(child_sjinfo->min_righthand);
+
+		if (child_sjinfo->syn_lefthand != parent_sjinfo->syn_lefthand)
+			bms_free(child_sjinfo->syn_lefthand);
+
+		if (child_sjinfo->syn_righthand != parent_sjinfo->syn_righthand)
+			bms_free(child_sjinfo->syn_righthand);
+
+		Assert(child_sjinfo->commute_above_l == parent_sjinfo->commute_above_l);
+		Assert(child_sjinfo->commute_above_r == parent_sjinfo->commute_above_r);
+		Assert(child_sjinfo->commute_below_l == parent_sjinfo->commute_below_l);
+		Assert(child_sjinfo->commute_below_r == parent_sjinfo->commute_below_r);
+
+		Assert(child_sjinfo->semi_operators == parent_sjinfo->semi_operators);
 
 		/*
 		 * semi_rhs_exprs may in principle be freed, but a simple pfree() does
@@ -1773,7 +1789,7 @@ free_child_join_sjinfo(SpecialJoinInfo *sjinfo)
 		 */
 	}
 
-	pfree(sjinfo);
+	pfree(child_sjinfo);
 }
 
 /*