Bug #65030 Innodb_buffer_pool_pages_flushed reports incorrect number of flushed pages

Description:
The value of Innodb_buffer_pool_pages_flushed is twice the value it should as flushed pages are being counted twice.

The internal srv_buf_pool_flushed counter is being increased twice for each flush batch, once in buf_flush_batch and once in buf_flush_common.

How to repeat:
mysql> SHOW GLOBAL STATUS WHERE Variable_name LIKE 'Innodb_pages_written' OR Variable_name LIKE 'Innodb_buffer_pool_pages_flushed';
+----------------------------------+-------+
| Variable_name                    | Value |
+----------------------------------+-------+
| Innodb_buffer_pool_pages_flushed | 20    |
| Innodb_pages_written             | 10    |
+----------------------------------+-------+
2 rows in set (0.00 sec)

mysql> INSERT INTO t1 VALUES (1);
Query OK, 1 row affected (0.00 sec)

mysql> SHOW GLOBAL STATUS WHERE Variable_name LIKE 'Innodb_pages_written' OR Variable_name LIKE 'Innodb_buffer_pool_pages_flushed';
+----------------------------------+-------+
| Variable_name                    | Value |
+----------------------------------+-------+
| Innodb_buffer_pool_pages_flushed | 32    |
| Innodb_pages_written             | 16    |
+----------------------------------+-------+
2 rows in set (0.00 sec)

Suggested fix:
--- a/storage/innobase/buf/buf0flu.c
+++ b/storage/innobase/buf/buf0flu.c
@@ -1749,8 +1749,6 @@ buf_flush_batch(
        }
 #endif /* UNIV_DEBUG */
 
-       srv_buf_pool_flushed += count;
-
        return(count);
 }

Thank you for the bug report and code contributed. Similar results with 5.5.23:

C:\Program Files\MySQL\MySQL Server 5.5\bin>net start mysql55
The MySQL55 service is starting..
The MySQL55 service was started successfully.

C:\Program Files\MySQL\MySQL Server 5.5\bin>mysql -uroot -proot -P3312 test
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.5.23-log MySQL Community Server (GPL)

Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> SHOW GLOBAL STATUS WHERE Variable_name LIKE 'Innodb_pages_written' OR
    -> Variable_name LIKE 'Innodb_buffer_pool_pages_flushed';
+----------------------------------+-------+
| Variable_name                    | Value |
+----------------------------------+-------+
| Innodb_buffer_pool_pages_flushed | 0     |
| Innodb_pages_written             | 0     |
+----------------------------------+-------+
2 rows in set (0.00 sec)

mysql> create table t(c1 int) engine=InnoDB;
Query OK, 0 rows affected (0.11 sec)

mysql> SHOW GLOBAL STATUS WHERE Variable_name LIKE 'Innodb_pages_written' OR
    -> Variable_name LIKE 'Innodb_buffer_pool_pages_flushed';
+----------------------------------+-------+
| Variable_name                    | Value |
+----------------------------------+-------+
| Innodb_buffer_pool_pages_flushed | 20    |
| Innodb_pages_written             | 10    |
+----------------------------------+-------+
2 rows in set (0.00 sec)

mysql> SHOW GLOBAL STATUS WHERE Variable_name LIKE 'Innodb_pages_written' OR
    -> Variable_name LIKE 'Innodb_buffer_pool_pages_flushed';
+----------------------------------+-------+
| Variable_name                    | Value |
+----------------------------------+-------+
| Innodb_buffer_pool_pages_flushed | 20    |
| Innodb_pages_written             | 10    |
+----------------------------------+-------+
2 rows in set (0.00 sec)

mysql> insert into t values(1);
Query OK, 1 row affected (0.06 sec)

... wait few seconds

mysql> SHOW GLOBAL STATUS WHERE Variable_name LIKE 'Innodb_pages_written' OR
    -> Variable_name LIKE 'Innodb_buffer_pool_pages_flushed';
+----------------------------------+-------+
| Variable_name                    | Value |
+----------------------------------+-------+
| Innodb_buffer_pool_pages_flushed | 28    |
| Innodb_pages_written             | 14    |
+----------------------------------+-------+
2 rows in set (0.00 sec)

Added to changelog for 5.5.25: 

The Innodb_buffer_pool_pages_flushed status variable was incorrectly
set to twice the value it should be. Its value should never exceed
the value of Innodb_pages_written.