Fix dirty page accounting leak with ext3 data=journal

patch a2b34564 in mainline.

In 46d2277c, try_to_free_buffers was
changed to bail out if the page was dirty. That caused
truncate_complete_page to leak massive amounts of memory, because the
dirty bit was only cleared after the call to try_to_free_buffers. So the
call to cancel_dirty_page was moved up to have the dirty bit cleared
early in 3e67c098.

The problem with that fix is, that the page can be redirtied after
cancel_dirty_page was called, eg. like this:

truncate_complete_page()
  cancel_dirty_page() // PG_dirty cleared, decr. dirty pages
  do_invalidatepage()
    ext3_invalidatepage()
      journal_invalidatepage()
        journal_unmap_buffer()
          __dispose_buffer()
            __journal_unfile_buffer()
              __journal_temp_unlink_buffer()
                mark_buffer_dirty(); // PG_dirty set, incr. dirty pages

And then we end up with dirty pages being wrongly accounted.

In ecdfc978 the changes to
try_to_free_buffers were reverted, so the original reason for the
massive memory leak is gone, so we can also revert the move of
the call to cancel_dirty_page from truncate_complete_page and get the
accounting right again.

Signed-off-by: Björn Steinbrink <B.Steinbrink@gmx.de>
Tested-by: Krzysztof Piotr Oledzki <ole@ans.pl>
Tested-by: Zaid D. <zaid.box@gmail.com>
Cc: Jan Kara <jack@ucw.cz>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Osterried <osterried@jesse.de>
Cc: Kerin Millar <kerframil@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>