MDEV-25837 Assertion `thd->locked_tables_mode == LTM_NONE' failed in Locked_tables_list::init_locked_tables.

don't do prelocking for the FLUSH command.

Author: Alexey Botchkov

mysql-test/main/flush.result

@@ -606,6 +606,17 @@ drop view v1, v2;
 drop table t1;
 disconnect con1;
 #
+# MDEV-25837 Assertion `thd->locked_tables_mode == LTM_NONE' failed in Locked_tables_list::init_locked_tables.
+#
+CREATE FUNCTION f() RETURNS INTEGER RETURN 1;
+CREATE TABLE t (a INT);
+CREATE VIEW v AS SELECT 2 FROM t WHERE f() < 3;
+FLUSH TABLE v WITH READ LOCK;
+UNLOCK TABLES;
+DROP VIEW v;
+DROP FUNCTION f;
+DROP TABLE t;
+#
 # Test FLUSH THREADS
 #
 set @save_thread_cache_size=@@global.thread_cache_size;

mysql-test/main/flush.test

@@ -722,6 +722,19 @@ drop view v1, v2;
 drop table t1;
 disconnect con1;
 
+--echo #
+--echo # MDEV-25837 Assertion `thd->locked_tables_mode == LTM_NONE' failed in Locked_tables_list::init_locked_tables.
+--echo #
+
+CREATE FUNCTION f() RETURNS INTEGER RETURN 1;
+CREATE TABLE t (a INT);
+CREATE VIEW v AS SELECT 2 FROM t WHERE f() < 3;
+FLUSH TABLE v WITH READ LOCK;
+ 
+UNLOCK TABLES;
+DROP VIEW v;
+DROP FUNCTION f;
+DROP TABLE t;
 
 --echo #
 --echo # Test FLUSH THREADS

sql/sql_base.cc

@@ -5553,7 +5553,8 @@ bool lock_tables(THD *thd, TABLE_LIST *tables, uint count, uint flags)
     DEBUG_SYNC(thd, "after_lock_tables_takes_lock");
 
     if (thd->lex->requires_prelocking() &&
-        thd->lex->sql_command != SQLCOM_LOCK_TABLES)
+        thd->lex->sql_command != SQLCOM_LOCK_TABLES &&
+        thd->lex->sql_command != SQLCOM_FLUSH)
     {
       /*
         We just have done implicit LOCK TABLES, and now we have