Fix bug in INSERT DELAYED with prepared statements

The bug was that if you have two TL_WRITE_DELAYED at the same time,
mi_lock_databases() could be done in the wrong order and we could write the wrong header to the MyISAM index file.

sql/mysql_priv.h

@@ -725,6 +725,7 @@ void wait_for_refresh(THD *thd);
 int open_tables(THD *thd, TABLE_LIST *tables, uint *counter);
 int simple_open_n_lock_tables(THD *thd,TABLE_LIST *tables);
 int open_and_lock_tables(THD *thd,TABLE_LIST *tables);
+int open_normal_and_derived_tables(THD *thd, TABLE_LIST *tables);
 void relink_tables_for_derived(THD *thd);
 int lock_tables(THD *thd, TABLE_LIST *tables, uint counter);
 TABLE *open_temporary_table(THD *thd, const char *path, const char *db,

sql/sql_base.cc

@@ -1702,6 +1702,34 @@ int open_and_lock_tables(THD *thd, TABLE_LIST *tables)
 }
 
 
+/*
+  Open all tables in list and process derived tables
+
+  SYNOPSIS
+    open_normal_and_derived_tables
+    thd		- thread handler
+    tables	- list of tables for open&locking
+
+  RETURN
+    FALSE - ok
+    TRUE  - error
+
+  NOTE 
+    This is to be used on prepare stage when you don't read any
+    data from the tables.
+*/
+
+int open_normal_and_derived_tables(THD *thd, TABLE_LIST *tables)
+{
+  uint counter;
+  DBUG_ENTER("open_normal_and_derived_tables");
+  if (open_tables(thd, tables, &counter))
+    DBUG_RETURN(-1);				/* purecov: inspected */
+  relink_tables_for_derived(thd);
+  DBUG_RETURN(mysql_handle_derived(thd->lex));
+}
+
+
 /*
   Let us propagate pointers to open tables from global table list
   to table lists in particular selects if needed.

sql/sql_prepare.cc

@@ -897,8 +897,12 @@ static int mysql_test_insert(Prepared_statement *stmt,
   /*
      open temporary memory pool for temporary data allocated by derived
      tables & preparation procedure
+     Note that this is done without locks (should not be needed as we will not
+     access any data here)
+     If we would use locks, then we have to ensure we are not using
+     TL_WRITE_DELAYED as having two such locks can cause table corruption.
   */
-  if (open_and_lock_tables(thd, table_list))
+  if (open_normal_and_derived_tables(thd, table_list))
   {
     DBUG_RETURN(-1);
   }