MDEV-39542 Assertion failed in trx_flush_log_if_needed()

trx_flush_log_if_needed(): Correct a debug assertion.

Author: dr-m

mysql-test/suite/innodb/r/dml_function.result

@@ -0,0 +1,26 @@
+#
+# MDEV-39542 Assertion failed in trx_flush_log_if_needed()
+#
+CREATE TABLE t (id INT) ENGINE=InnoDB;
+INSERT INTO t VALUES (1),(2),(3);
+CREATE FUNCTION f(i INT) RETURNS INT
+BEGIN
+SET TRANSACTION READ ONLY;
+RETURN i;
+END //
+CREATE FUNCTION g(i INT) RETURNS INT
+BEGIN
+START TRANSACTION READ ONLY;
+RETURN i;
+END //
+ERROR HY000: Explicit or implicit commit is not allowed in stored function or trigger
+DELETE FROM t WHERE id=f(1);
+DELETE FROM t WHERE id=2;
+SET TRANSACTION READ ONLY;
+DELETE FROM t WHERE id=3;
+ERROR 25006: Cannot execute statement in a READ ONLY transaction
+SELECT * FROM t;
+id
+3
+DROP FUNCTION f;
+DROP TABLE t;

mysql-test/suite/innodb/t/dml_function.test

@@ -0,0 +1,31 @@
+--source include/have_innodb.inc
+
+--echo #
+--echo # MDEV-39542 Assertion failed in trx_flush_log_if_needed()
+--echo #
+CREATE TABLE t (id INT) ENGINE=InnoDB;
+INSERT INTO t VALUES (1),(2),(3);
+--delimiter //
+CREATE FUNCTION f(i INT) RETURNS INT
+BEGIN
+SET TRANSACTION READ ONLY;
+RETURN i;
+END //
+
+--error ER_COMMIT_NOT_ALLOWED_IN_SF_OR_TRG
+CREATE FUNCTION g(i INT) RETURNS INT
+BEGIN
+START TRANSACTION READ ONLY;
+RETURN i;
+END //
+
+--delimiter ;
+DELETE FROM t WHERE id=f(1);
+# MDEV-39649 FIXME: The SET TRANSACTION READ ONLY in f(1) was ignored!
+DELETE FROM t WHERE id=2;
+SET TRANSACTION READ ONLY;
+--error ER_CANT_EXECUTE_IN_READ_ONLY_TRANSACTION
+DELETE FROM t WHERE id=3;
+SELECT * FROM t;
+DROP FUNCTION f;
+DROP TABLE t;

storage/innobase/trx/trx0trx.cc

@@ -1257,7 +1257,7 @@ static void trx_flush_log_if_needed(lsn_t lsn, trx_t *trx)
   if (log_sys.get_flushed_lsn(std::memory_order_relaxed) >= lsn)
     return;
 
-  ut_ad(!trx->mysql_thd || !trx->mysql_thd->tx_read_only);
+  ut_ad(!trx->read_only);
 
   const bool flush=
     (srv_file_flush_method != SRV_NOSYNC &&