From: Anton Altaparmakov <aia21@cam.ac.uk>

A filesystem's ->writepage() implementation nowadays must run either
redirty_page_for_writepage() or the combination of set_page_writeback()/
end_page_writeback().  Failure to do so leaves the page itself marked clean
but it is tagged as dirty in the radix tree (PAGECACHE_TAG_DIRTY).  This
incoherency can lead to all sorts of hard-to-debug problems in the
filesystem like having dirty inodes at umount and losing written data.

The patch updates Documentation/filesystems/Locking to reflect this
requirement.
Signed-off-by: Anton Altaparmakov <aia21@cantab.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>