Fix that BACKUP STAGE BLOCK_COMMIT flushes binary log

mysql-test/suite/binlog/r/backup.result

+#
+# Test BACKUP STAGES BLOCK_COMMIT with binary logging on
+#
+SET BINLOG_FORMAT=MIXED;
+RESET MASTER;
+create table t1 (a int) engine=aria;
+insert into t1 values (1);
+BACKUP STAGE START;
+BACKUP STAGE BLOCK_COMMIT;
+SELECT @@gtid_binlog_pos;
+@@gtid_binlog_pos
+0-1-2
+BACKUP STAGE END;
+include/show_binlog_events.inc
+Log_name	Pos	Event_type	Server_id	End_log_pos	Info
+master-bin.000001	#	Gtid	#	#	GTID #-#-#
+master-bin.000001	#	Query	#	#	use `test`; create table t1 (a int) engine=aria
+master-bin.000001	#	Gtid	#	#	BEGIN GTID #-#-#
+master-bin.000001	#	Query	#	#	use `test`; insert into t1 values (1)
+master-bin.000001	#	Query	#	#	COMMIT
+drop table t1;

mysql-test/suite/binlog/t/backup.test

+--source include/have_log_bin.inc
+--source include/have_binlog_format_mixed.inc
+
+--echo #
+--echo # Test BACKUP STAGES BLOCK_COMMIT with binary logging on
+--echo #
+
+SET BINLOG_FORMAT=MIXED;
+RESET MASTER;
+
+create table t1 (a int) engine=aria;
+insert into t1 values (1);
+
+BACKUP STAGE START;
+BACKUP STAGE BLOCK_COMMIT;
+SELECT @@gtid_binlog_pos;
+BACKUP STAGE END;
+source include/show_binlog_events.inc;
+drop table t1;

sql/backup.cc

@@ -290,6 +290,14 @@ static bool backup_block_commit(THD *thd)
 
   /* We can ignore errors from flush_tables () */
   (void) flush_tables(thd, FLUSH_SYS_TABLES);
+
+  if (mysql_bin_log.is_open())
+  {
+    mysql_mutex_lock(mysql_bin_log.get_log_lock());
+    mysql_file_sync(mysql_bin_log.get_log_file()->file,
+                    MYF(MY_WME|MY_SYNC_FILESIZE));
+    mysql_mutex_unlock(mysql_bin_log.get_log_lock());
+  }
   thd->clear_error();
 
   DBUG_RETURN(0);