Bug #44613 SELECT statement inside FUNCTION takes a shared lock

The problem was that a shared InnoDB row lock was taken when executing
SELECT statements inside a stored function as a part of a transaction
using REPEATABLE READ. This prevented other transactions from updating
the row.

InnoDB uses multi-versioning and consistent nonlocking reads. SELECTs
should therefore not acquire locks and block other transactions
wishing to do updates.

This bug is no longer repeatable with the changes introduced in the scope
of metadata locking.

Test case added to innodb_mysql.test.

mysql-test/r/innodb_mysql.result

@@ -2297,3 +2297,28 @@ t2	CREATE TABLE `t2` (
   CONSTRAINT `x` FOREIGN KEY (`fk`) REFERENCES `t1` (`pk`)
 ) ENGINE=InnoDB DEFAULT CHARSET=latin1
 drop table t2, t1;
+#
+# Bug#44613 SELECT statement inside FUNCTION takes a shared lock
+#
+DROP TABLE IF EXISTS t1;
+DROP FUNCTION IF EXISTS f1;
+CREATE TABLE t1(x INT PRIMARY KEY, y INT) ENGINE=innodb;
+INSERT INTO t1 VALUES (1, 0), (2, 0);
+CREATE FUNCTION f1(z INT) RETURNS INT READS SQL DATA
+RETURN (SELECT x FROM t1 WHERE x = z);
+# Connection default
+START TRANSACTION;
+SELECT f1(1);
+f1(1)
+1
+# Connection con2
+START TRANSACTION;
+SELECT f1(1);
+f1(1)
+1
+UPDATE t1 SET y = 1 WHERE x = 1;
+COMMIT;
+# Connection default
+COMMIT;
+DROP TABLE t1;
+DROP FUNCTION f1;

mysql-test/t/innodb_mysql.test

@@ -555,3 +555,42 @@ create table t2 (fk int, key x (fk),
                  constraint x foreign key (FK) references t1 (PK)) engine=InnoDB;
 show create table t2;
 drop table t2, t1;
+
+
+--echo #
+--echo # Bug#44613 SELECT statement inside FUNCTION takes a shared lock
+--echo #
+
+--disable_warnings
+DROP TABLE IF EXISTS t1;
+DROP FUNCTION IF EXISTS f1;
+--enable_warnings
+
+CREATE TABLE t1(x INT PRIMARY KEY, y INT) ENGINE=innodb;
+INSERT INTO t1 VALUES (1, 0), (2, 0);
+
+CREATE FUNCTION f1(z INT) RETURNS INT READS SQL DATA
+  RETURN (SELECT x FROM t1 WHERE x = z);
+
+--echo # Connection default
+START TRANSACTION;
+SELECT f1(1);
+
+--echo # Connection con2
+--disable_query_log
+connect (con2, localhost, root);
+--enable_query_log
+START TRANSACTION;
+SELECT f1(1);
+# This next statement used to block.
+UPDATE t1 SET y = 1 WHERE x = 1;
+
+COMMIT;
+
+disconnect con2;
+--source include/wait_until_disconnected.inc
+--echo # Connection default
+connection default;
+COMMIT;
+DROP TABLE t1;
+DROP FUNCTION f1;