[PATCH] hold the page ref across ->readpage

read_pages() is dropping the page refcount before running ->readpage().
Which just happens to work, because the page is in pagecache and
locked.

But it breaks under some unconventional things which reiser4 is doing,
and it's better/safer/saner this way anyway.

mm/readahead.c

@@ -48,9 +48,9 @@ read_pages(struct file *file, struct address_space *mapping,
 		struct page *page = list_entry(pages->prev, struct page, list);
 		list_del(&page->list);
 		if (!add_to_page_cache(page, mapping, page->index)) {
+			mapping->a_ops->readpage(file, page);
 			if (!pagevec_add(&lru_pvec, page))
 				__pagevec_lru_add(&lru_pvec);
-			mapping->a_ops->readpage(file, page);
 		} else {
 			page_cache_release(page);
 		}