From 99f332fc9a5ad546a0660cd6a7a4cdb76369c79f Mon Sep 17 00:00:00 2001
From: Masahiko Sawada <sawada.mshk@gmail.com>
Date: Tue, 23 Sep 2025 12:23:16 -0700
Subject: [PATCH v5] postgres_fdw: Fix assertion failure when EvalPlanQual with
 a SubLink sub-select.

Reported-by: Kristian Lejao <kristianlejao@gmail.com>
Author: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-by: Etsuro Fujita <etsuro.fujita@gmail.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/CAD21AoBpo6Gx55FBOW+9s5X=nUw3Xpq64v35fpDEKsTERnc4TQ@mail.gmail.com
---
 contrib/postgres_fdw/Makefile                 |  3 +
 .../postgres_fdw/expected/eval_plan_qual.out  | 25 ++++++++
 contrib/postgres_fdw/meson.build              |  6 ++
 .../postgres_fdw/specs/eval_plan_qual.spec    | 58 +++++++++++++++++++
 src/include/executor/execScan.h               | 23 +++++---
 5 files changed, 107 insertions(+), 8 deletions(-)
 create mode 100644 contrib/postgres_fdw/expected/eval_plan_qual.out
 create mode 100644 contrib/postgres_fdw/specs/eval_plan_qual.spec

diff --git a/contrib/postgres_fdw/Makefile b/contrib/postgres_fdw/Makefile
index adfbd2ef758..81df6ca9085 100644
--- a/contrib/postgres_fdw/Makefile
+++ b/contrib/postgres_fdw/Makefile
@@ -16,6 +16,9 @@ SHLIB_LINK_INTERNAL = $(libpq)
 EXTENSION = postgres_fdw
 DATA = postgres_fdw--1.0.sql postgres_fdw--1.0--1.1.sql postgres_fdw--1.1--1.2.sql
 
+ISOLATION = eval_plan_qual
+ISOLATION_OPTS = --load-extension=postgres_fdw
+
 REGRESS = postgres_fdw query_cancel
 TAP_TESTS = 1
 
diff --git a/contrib/postgres_fdw/expected/eval_plan_qual.out b/contrib/postgres_fdw/expected/eval_plan_qual.out
new file mode 100644
index 00000000000..385b1a03981
--- /dev/null
+++ b/contrib/postgres_fdw/expected/eval_plan_qual.out
@@ -0,0 +1,25 @@
+Parsed test spec with 2 sessions
+
+starting permutation: s0_begin s0_update s1_begin s1_tuplock s0_commit s1_commit
+step s0_begin: BEGIN ISOLATION LEVEL READ COMMITTED;
+step s0_update: UPDATE a SET i = i + 1;
+step s1_begin: BEGIN ISOLATION LEVEL READ COMMITTED;
+step s1_tuplock: 
+    EXPLAIN (COSTS OFF, ANALYZE ON, TIMING OFF, SUMMARY OFF, BUFFERS OFF)
+    SELECT a.i,
+       (SELECT 1 FROM fb, fc WHERE a.i = fb.i AND fb.i = fc.i)
+    FROM a as a
+    FOR UPDATE;
+ <waiting ...>
+step s0_commit: COMMIT;
+step s1_tuplock: <... completed>
+QUERY PLAN                                           
+-----------------------------------------------------
+LockRows (actual rows=1.00 loops=1)                  
+  ->  Seq Scan on a (actual rows=1.00 loops=1)       
+        SubPlan 1                                    
+          ->  Foreign Scan (actual rows=1.00 loops=1)
+                Relations: (fb) INNER JOIN (fc)      
+(5 rows)
+
+step s1_commit: COMMIT;
diff --git a/contrib/postgres_fdw/meson.build b/contrib/postgres_fdw/meson.build
index 5c11bc6496f..aac89ffdde8 100644
--- a/contrib/postgres_fdw/meson.build
+++ b/contrib/postgres_fdw/meson.build
@@ -41,6 +41,12 @@ tests += {
     ],
     'regress_args': ['--dlpath', meson.project_build_root() / 'src/test/regress'],
   },
+  'isolation': {
+    'specs': [
+      'eval_plan_qual',
+    ],
+    'regress_args': ['--load-extension=postgres_fdw'],
+  },
   'tap': {
     'tests': [
       't/001_auth_scram.pl',
diff --git a/contrib/postgres_fdw/specs/eval_plan_qual.spec b/contrib/postgres_fdw/specs/eval_plan_qual.spec
new file mode 100644
index 00000000000..6552bd605f4
--- /dev/null
+++ b/contrib/postgres_fdw/specs/eval_plan_qual.spec
@@ -0,0 +1,58 @@
+# Tests for the EvalPlanQual mechanism involving foreign tables
+
+setup
+{
+    DO $d$
+    BEGIN
+        EXECUTE $$CREATE SERVER loopback FOREIGN DATA WRAPPER postgres_fdw
+            OPTIONS (dbname '$$||current_database()||$$',
+                port '$$||current_setting('port')||$$'
+            )$$;
+    END;
+    $d$;
+    CREATE USER MAPPING FOR public SERVER loopback;
+
+    CREATE TABLE a (i int);
+    CREATE TABLE b (i int);
+    CREATE TABLE c (i int);
+    CREATE FOREIGN TABLE fb (i int) SERVER loopback OPTIONS (table_name 'b');
+    CREATE FOREIGN TABLE fc (i int) SERVER loopback OPTIONS (table_name 'c');
+
+    INSERT INTO a VALUES (1);
+    INSERT INTO b VALUES (1);
+    INSERT INTO c VALUES (1);
+}
+
+teardown
+{
+    DROP TABLE a;
+    DROP TABLE b;
+    DROP TABLE c;
+    DROP SERVER loopback CASCADE;
+}
+
+session s0
+step s0_begin { BEGIN ISOLATION LEVEL READ COMMITTED; }
+step s0_commit { COMMIT; }
+step s0_update { UPDATE a SET i = i + 1; }
+
+
+session s1
+step s1_begin { BEGIN ISOLATION LEVEL READ COMMITTED; }
+step s1_tuplock {
+    -- Verify if the sub-select has a foreign-join
+    EXPLAIN (VERBOSE, COSTS OFF)
+    SELECT a.i,
+       (SELECT 1 FROM fb, fc WHERE a.i = fb.i AND fb.i = fc.i)
+    FROM a as a
+    FOR UPDATE;
+    SELECT a.i,
+       (SELECT 1 FROM fb, fc WHERE a.i = fb.i AND fb.i = fc.i)
+    FROM a as a
+    FOR UPDATE;
+}
+step s1_commit { COMMIT; }
+
+# This test exercises EvalPlanQual with a SubLink sub-select (which should
+# be unaffected by any EPQ recheck behavior in the outer query)
+permutation s0_begin s0_update s1_begin s1_tuplock s0_commit s1_commit
diff --git a/src/include/executor/execScan.h b/src/include/executor/execScan.h
index 837ea7785bb..95866e13ed4 100644
--- a/src/include/executor/execScan.h
+++ b/src/include/executor/execScan.h
@@ -49,16 +49,23 @@ ExecScanFetch(ScanState *node,
 		{
 			/*
 			 * This is a ForeignScan or CustomScan which has pushed down a
-			 * join to the remote side.  The recheck method is responsible not
-			 * only for rechecking the scan/join quals but also for storing
-			 * the correct tuple in the slot.
+			 * join to the remote side. If it is a descendant node in the EPQ
+			 * recheck plan tree, run the recheck method function. Otherwise,
+			 * run the access method function below.
 			 */
+			if (bms_is_member(epqstate->epqParam, node->ps.plan->extParam))
+			{
+				/*
+				 * The recheck method is responsible not only for rechecking
+				 * the scan/join quals but also for storing the correct tuple
+				 * in the slot.
+				 */
+				TupleTableSlot *slot = node->ss_ScanTupleSlot;
 
-			TupleTableSlot *slot = node->ss_ScanTupleSlot;
-
-			if (!(*recheckMtd) (node, slot))
-				ExecClearTuple(slot);	/* would not be returned by scan */
-			return slot;
+				if (!(*recheckMtd) (node, slot))
+					ExecClearTuple(slot);	/* would not be returned by scan */
+				return slot;
+			}
 		}
 		else if (epqstate->relsubs_done[scanrelid - 1])
 		{
-- 
2.47.3

