[PATCH] mpage_writepages() page locking fix

When ->writepage() returns WRITEPAGE_ACTIVATE, the page is still locked.
Explicitly unlock the page in mpage_writepages().
Signed-off-by: Nikita Danilov <nikita@clusterfs.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/mpage.c

@@ -727,6 +727,8 @@ __mpage_writepages(struct address_space *mapping,
 						&last_block_in_bio, &ret, wbc,
 						writepage_fn);
 			}
+			if (unlikely(ret == WRITEPAGE_ACTIVATE))
+				unlock_page(page);
 			if (ret || (--(wbc->nr_to_write) <= 0))
 				done = 1;
 			if (wbc->nonblocking && bdi_write_congested(bdi)) {