0001-Repro-backend-stuck-waiting-on-submitted-IO-with-io_.patch

From 98704151ae72b3cfa4a5fb85706fe5bca6c7998c Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Mon, 22 Sep 2025 17:08:58 +0300
Subject: [PATCH 1/1] Repro backend stuck waiting on submitted IO with io_uring

---
 src/test/modules/test_aio/t/001_aio.pl | 58 ++++++++++++++++++++++++++
 src/test/modules/test_aio/test_aio.c   | 11 ++++-
 2 files changed, 68 insertions(+), 1 deletion(-)

diff --git a/src/test/modules/test_aio/t/001_aio.pl b/src/test/modules/test_aio/t/001_aio.pl
index 3f0453619e8..1fcf02aafdb 100644
--- a/src/test/modules/test_aio/t/001_aio.pl
+++ b/src/test/modules/test_aio/t/001_aio.pl
@@ -673,6 +673,63 @@ sub test_complete_foreign
 	$psql_b->quit();
 }
 
+# 1. Backend A stages an IO
+# 2. Backend B blocks waiting on it
+# 3. Backend A submits the IO, but does not wait for it to complete
+# 4. Backend B should complete the IO
+sub test_wait_staged
+{
+	my $io_method = shift;
+	my $node = shift;
+	my ($ret, $output);
+
+	my $psql_a = $node->background_psql('postgres', on_error_stop => 0);
+	# 10 s timeout to make the test faster if backend B gets stuck waiting for IO
+	my $psql_b = $node->background_psql('postgres', on_error_stop => 0, timeout => 10);
+
+	# To warm the catalog caches
+	$psql_a->query_safe(
+		qq(SELECT read_rel_block_ll('tbl_ok', 2, wait_complete=>true);));
+
+	# Start a new batch
+	$psql_a->query_safe(
+		qq(begin));
+	$psql_a->query_safe(
+		qq(SELECT WHERE batch_start() IS NULL));
+
+	# Stage IO without submitting it yet
+	$psql_a->query_safe(
+		qq(SELECT read_rel_block_ll('tbl_ok', 1, batchmode_enter=>false, wait_complete=>false);));
+
+	# Start reading the same block in another backend. It sees the IO as "staged" by backend
+	# A, and blocks waiting on it.
+	$psql_b->query_until(
+		qr/start/, q{
+	\echo start
+    BEGIN;
+    SELECT read_rel_block_ll('tbl_ok', 1, wait_complete=>true);
+    SELECT 'SUCCESS';
+    COMMIT;
+});
+
+	# make sure psql_b has blocked on the IO
+	sleep(1);
+
+	# Cause the IO we staged in backend A to be submitted, but don't wait for its completion
+	$psql_a->query_safe(
+		qq(rollback));
+
+	# Wait for the IO on backend B to complete.
+	pump_until(
+			$psql_b->{run}, $psql_b->{timeout},
+		\$psql_b->{stdout}, qr/SUCCESS/);
+#	$psql_b->{stderr} = '';
+    ok(1, "$io_method: backend B sees the io staged and later submitted by backend A as completed");
+
+	$psql_a->quit();
+	$psql_b->quit();
+}
+
 # Test that we deal correctly with FDs being closed while IO is in progress
 sub test_close_fd
 {
@@ -1525,6 +1582,7 @@ CHECKPOINT;
 	test_checksum($io_method, $node);
 	test_ignore_checksum($io_method, $node);
 	test_checksum_createdb($io_method, $node);
+	test_wait_staged($io_method, $node);
 
   SKIP:
 	{
diff --git a/src/test/modules/test_aio/test_aio.c b/src/test/modules/test_aio/test_aio.c
index c55cf6c0aac..63ca3499815 100644
--- a/src/test/modules/test_aio/test_aio.c
+++ b/src/test/modules/test_aio/test_aio.c
@@ -374,11 +374,18 @@ read_rel_block_ll(PG_FUNCTION_ARGS)
 	PgAioHandle *ioh;
 	PgAioWaitRef iow;
 	SMgrRelation smgr;
+	ResourceOwner save_resowner = CurrentResourceOwner;
+
+	/*
+	 * Associate the IO with top-transaction owner, so that if you call
+	 * batch_start() before this, the IO gets staged in the batch.
+	 */
+	CurrentResourceOwner = TopTransactionResourceOwner;
 
 	if (nblocks <= 0 || nblocks > PG_IOV_MAX)
 		elog(ERROR, "nblocks is out of range");
 
-	rel = relation_open(relid, AccessExclusiveLock);
+	rel = relation_open(relid, AccessShareLock);
 
 	for (int i = 0; i < nblocks; i++)
 	{
@@ -449,6 +456,8 @@ read_rel_block_ll(PG_FUNCTION_ARGS)
 
 	relation_close(rel, NoLock);
 
+	CurrentResourceOwner = save_resowner;
+
 	PG_RETURN_VOID();
 }
 
-- 
2.47.3