MDEV-14959: Fixed memory leak relating with view and IS

Fixed memory leak taken place on executing a prepared statement or
a stored routine that querying a view and this view constructed
on an information schema table. For example,

Lets consider the following definition of the view 'v1'
CREATE VIEW v1 AS SELECT table_name FROM information_schema.views
ORDER BY table_name;

Querying this view in PS mode result in hit of assert.
PREPARE stmt FROM "SELECT * FROM v1";
EXECUTE stmt;
EXECUTE stmt; (*)

Running the statement marked with (*) leads to a crash in case
server build with mode to control allocation of a memory from SP/PS
memory root on the second and following executions of PS/SP.

The reason of leaking the memory is that a memory allocated on
processing of FRM file for the view requested from a PS/PS memory
root meaning that this memory be released only when a stored routine
be evicted from SP-cache or a prepared statement be deallocated
that typically happens on termination of a user session.

To fix the issue switch to a memory root specially created for
allocation of short-lived objects that requested on parsing FRM.

sql/sql_show.cc

@@ -4955,7 +4955,8 @@ try_acquire_high_prio_shared_mdl_lock(THD *thd, TABLE_LIST *table,
                               open_tables function for this table
 */
 
-static int fill_schema_table_from_frm(THD *thd, TABLE *table,
+static int fill_schema_table_from_frm(THD *thd, MEM_ROOT *mem_root,
+                                      TABLE *table,
                                       ST_SCHEMA_TABLE *schema_table,
                                       LEX_CSTRING *db_name,
                                       LEX_CSTRING *table_name,
@@ -4967,6 +4968,9 @@ static int fill_schema_table_from_frm(THD *thd, TABLE *table,
   TABLE_LIST table_list;
   uint res= 0;
   char db_name_buff[NAME_LEN + 1], table_name_buff[NAME_LEN + 1];
+  Query_arena i_s_arena(mem_root, Query_arena::STMT_CONVENTIONAL_EXECUTION);
+  Query_arena backup_arena, *old_arena;
+  bool i_s_arena_active= false;
 
   bzero((char*) &table_list, sizeof(TABLE_LIST));
   bzero((char*) &tbl, sizeof(TABLE));
@@ -5041,6 +5045,11 @@ static int fill_schema_table_from_frm(THD *thd, TABLE *table,
     goto end;
   }
 
+  old_arena= thd->stmt_arena;
+  thd->stmt_arena= &i_s_arena;
+  thd->set_n_backup_active_arena(&i_s_arena, &backup_arena);
+  i_s_arena_active= true;
+
   share= tdc_acquire_share(thd, &table_list, GTS_TABLE | GTS_VIEW);
   if (!share)
   {
@@ -5122,7 +5131,16 @@ static int fill_schema_table_from_frm(THD *thd, TABLE *table,
     savepoint is safe.
   */
   DBUG_ASSERT(thd->open_tables == NULL);
+
   thd->mdl_context.rollback_to_savepoint(open_tables_state_backup->mdl_system_tables_svp);
+
+  if (i_s_arena_active)
+  {
+    thd->stmt_arena= old_arena;
+    thd->restore_active_arena(&i_s_arena, &backup_arena);
+    i_s_arena.free_items();
+  }
+
   if (!thd->is_fatal_error)
     thd->clear_error();
   return res;
@@ -5351,7 +5369,8 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
             if (!(table_open_method & ~OPEN_FRM_ONLY) &&
                 db_name != &INFORMATION_SCHEMA_NAME)
             {
-              if (!fill_schema_table_from_frm(thd, table, schema_table,
+              if (!fill_schema_table_from_frm(thd, &tmp_mem_root,
+                                              table, schema_table,
                                               db_name, table_name,
                                               &open_tables_state_backup,
                                               can_deadlock))