MDEV-14740 Locking assertion for system_time partitioning

Assertion `thd->locked_tables_mode <= LTM_LOCK_TABLES ||
!thd->lex->requires_prelocking()' failed in lock_tables().

mysql-test/suite/versioning/r/partition.result

@@ -345,5 +345,14 @@ create trigger tr before insert on t2
 for each row select table_rows from information_schema.tables
 where table_name = 't1' into @a;
 insert into t2 values (1);
+# MDEV-14740 Locking assertion for system_time partitioning
+create or replace table t1 (i int) with system versioning
+partition by system_time interval 1 week (
+partition p1 history,
+partition pn current);
+create or replace table t2 (f int);
+create trigger tr before insert on t2
+for each row select count(*) from t1 into @a;
+insert into t2 values (1);
 drop table t1;
 drop table t2;

mysql-test/suite/versioning/t/partition.test

@@ -293,6 +293,16 @@ for each row select table_rows from information_schema.tables
 where table_name = 't1' into @a;
 insert into t2 values (1);
 
+--echo # MDEV-14740 Locking assertion for system_time partitioning
+create or replace table t1 (i int) with system versioning
+partition by system_time interval 1 week (
+  partition p1 history,
+  partition pn current);
+create or replace table t2 (f int);
+create trigger tr before insert on t2
+for each row select count(*) from t1 into @a;
+insert into t2 values (1);
+
 
 drop table t1;
 drop table t2;

sql/partition_info.cc

@@ -1035,18 +1035,20 @@ class Table_locker
 {
   THD *thd;
   TABLE &table;
-  thr_lock_type saved_mode;
-  TABLE_LIST table_list;
+  thr_lock_type saved_type;
   MYSQL_LOCK *saved_lock;
+  enum_locked_tables_mode saved_mode;
+  TABLE_LIST table_list;
   bool locked;
 
 public:
   Table_locker(THD *_thd, TABLE &_table, thr_lock_type lock_type) :
     thd(_thd),
     table(_table),
-    saved_mode(table.reginfo.lock_type),
-    table_list(_table, lock_type),
+    saved_type(table.reginfo.lock_type),
     saved_lock(_thd->lock),
+    saved_mode(_thd->locked_tables_mode),
+    table_list(_table, lock_type),
     locked(false)
   {
     table.reginfo.lock_type= lock_type;
@@ -1066,8 +1068,9 @@ class Table_locker
   {
     if (locked)
       mysql_unlock_tables(thd, thd->lock);
-    table.reginfo.lock_type= saved_mode;
+    table.reginfo.lock_type= saved_type;
     thd->lock= saved_lock;
+    thd->locked_tables_mode= saved_mode;
     if (locked && !thd->in_sub_stmt)
       ha_commit_trans(thd, false);
   }