trx0roll.c:

  Put a sensible value of thread id and process no to a background rollback transaction

innobase/trx/trx0roll.c

@@ -454,6 +454,10 @@ loop:
 					(ulong) rows_to_undo, unit);
 	mutex_exit(&kernel_mutex);
 
+	trx->mysql_thread_id = os_thread_get_curr_id();
+
+	trx->mysql_process_no = os_proc_get_number();
+
 	if (trx->dict_operation) {
 		row_mysql_lock_data_dictionary(trx);
 	}