XtraDB hangs on Windows due to failing to release block->lock X-latch in innodb_read_only mode

The recently added test innodb.row_format_redundant hangs on XtraDB on Windows. InnoDB and other platforms than Windows seem to be fine.

Here is the problematic section:

SET GLOBAL innodb_fast_shutdown=0;

--let $restart_parameters = --innodb-read-only

--source include/restart_mysqld.inc

SELECT COUNT(*) FROM t1;

The query is blocked while trying to acquire an S-latch on a block->lock on a clustered index page. The X-latch was acquired by buf_page_init_for_read(), and normally it should be released by buf_page_io_complete(). Added debug output in that function confirms that the function was being invoked for some pages, but not this one.