Bug #27208858 CONCURRENT DDL/DML ON FOREIGN KEYS CRASH IN PAGE_CUR_SEARCH_WITH_MATCH_BYTES

PROBLEM
-------

1. During truncate when we are trying to flush out the pages
   of truncated table form the buffer pool we release the dict lock.
2. At this stage a DDL request  to add a FK constraint from another
   connection,tries to access the stale index memory object of the
   parent table and asserts.

FIX
---

 Disallow the DDL operation of adding FK when parent table is
 undergoing truncate .

 [#rb 19433 Reviewed by Jimmy ]

Author: Aditya A

storage/innobase/fil/fil0fil.cc

@@ -2997,6 +2997,7 @@ fil_reinit_space_header_for_table(
 	they won't violate the latch ordering. */
 	dict_table_x_unlock_indexes(table);
 	row_mysql_unlock_data_dictionary(trx);
+	DEBUG_SYNC_C("trunc_table_index_dropped_release_dict_lock");
 
 	/* Lock the search latch in shared mode to prevent user
 	from disabling AHI during the scan */

storage/innobase/row/row0ins.cc

@@ -1618,7 +1618,8 @@ row_ins_check_foreign_constraint(
 
 	if (check_table == NULL
 	    || check_table->ibd_file_missing
-	    || check_index == NULL) {
+	    || check_index == NULL
+	    || fil_space_is_being_truncated(check_table->space)) {
 
 		if (!srv_read_only_mode && check_ref) {
 			FILE*	ef = dict_foreign_err_file;
@@ -1640,7 +1641,8 @@ row_ins_check_foreign_constraint(
 			ut_print_name(ef, trx,
 				      foreign->referenced_table_name);
 			fputs("\nor its .ibd file does"
-			      " not currently exist!\n", ef);
+			      " not currently exist!, or"
+			      " is undergoing truncate!\n", ef);
 			mutex_exit(&dict_foreign_err_mutex);
 
 			err = DB_NO_REFERENCED_ROW;
@@ -1873,6 +1875,7 @@ row_ins_check_foreign_constraint(
 		mem_heap_free(heap);
 	}
 
+	DEBUG_SYNC_C("finished_scanning_index");
 	DBUG_RETURN(err);
 }