MDEV-17215 Assertion `rw_lock_own(dict_operation_lock, RW_LOCK_S)

			|| node->vcol_info.is_used()' failed

- Purge thread can acquire mdl lock while initializing the mysql template.
Set the vcol_info information before acquiring mdl lock.

- Purge thread doesn't need to use the virtual column info even though it is
requested. In that case, reset the virtual column info.

storage/innobase/handler/ha_innodb.cc

@@ -21458,13 +21458,12 @@ static TABLE* innodb_find_table_for_vc(THD* thd, dict_table_t* table)
 }
 
 /** Get the computed value by supplying the base column values.
-@param[in,out]	table	table whose virtual column template to be built */
-void
-innobase_init_vc_templ(
-	dict_table_t*	table)
+@param[in,out]	table		table whose virtual column
+				template to be built */
+TABLE* innobase_init_vc_templ(dict_table_t* table)
 {
 	if (table->vc_templ != NULL) {
-		return;
+		return NULL;
 	}
 
 	table->vc_templ = UT_NEW_NOKEY(dict_vcol_templ_t());
@@ -21473,12 +21472,13 @@ innobase_init_vc_templ(
 
 	ut_ad(mysql_table);
 	if (!mysql_table) {
-		return;
+		return NULL;
 	}
 
 	mutex_enter(&dict_sys->mutex);
 	innobase_build_v_templ(mysql_table, table, table->vc_templ, NULL, true);
 	mutex_exit(&dict_sys->mutex);
+	return mysql_table;
 }
 
 /** Change dbname and table name in table->vc_templ.

storage/innobase/include/row0mysql.h

@@ -915,10 +915,9 @@ innobase_get_computed_value(
 	dict_foreign_t*		foreign);
 
 /** Get the computed value by supplying the base column values.
-@param[in,out]	table	the table whose virtual column template to be built */
-void
-innobase_init_vc_templ(
-	dict_table_t*	table);
+@param[in,out]	table		the table whose virtual column
+				template to be built */
+TABLE* innobase_init_vc_templ(dict_table_t* table);
 
 /** Change dbname and table name in table->vc_templ.
 @param[in,out]	table	the table whose virtual column template

storage/innobase/row/row0purge.cc

@@ -375,6 +375,13 @@ row_purge_poss_sec(
 
 	ut_ad(mtr.has_committed());
 
+	/* If the virtual column info is not used then reset the virtual column
+	info. */
+	if (node->vcol_info.is_requested()
+	    && !node->vcol_info.is_used()) {
+		node->vcol_info.reset();
+	}
+
 	if (store_cur && !row_purge_restore_vsec_cur(
 		    node, index, sec_pcur, sec_mtr, is_tree)) {
 		return false;
@@ -1017,8 +1024,10 @@ row_purge_parse_undo_rec(
 			goto try_again;
 		}
 
-		/* Initialize the template for the table */
-		innobase_init_vc_templ(node->table);
+		node->vcol_info.set_requested();
+		node->vcol_info.set_used();
+		node->vcol_info.set_table(innobase_init_vc_templ(node->table));
+		node->vcol_info.set_used();
 	}
 
 	clust_index = dict_table_get_first_index(node->table);