[patch] mm: vmscan fix mapping use after free

[Nick Piggin <npiggin@suse.de>]

On Tue, Jun 15, 2010 at 03:12:42PM +1000, Nick Piggin wrote:
> > Once that page is unlocked, we can't touch *mapping - its inode can be
> > concurrently reclaimed.  Although I guess the technique in
> > handle_write_error() can be reused.
> 
> Nasty. That guy needs to be using lock_page_nosync().
--

Need lock_page_nosync here because we have no reference to the mapping when
taking the page lock.

Signed-off-by: Nick Piggin <npiggin@suse.de>

---
 mm/vmscan.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6/mm/vmscan.c
===================================================================
--- linux-2.6.orig/mm/vmscan.c
+++ linux-2.6/mm/vmscan.c
@@ -296,7 +296,7 @@ static int may_write_to_queue(struct bac
 static void handle_write_error(struct address_space *mapping,
 				struct page *page, int error)
 {
-	lock_page(page);
+	lock_page_nosync(page);
 	if (page_mapping(page) == mapping)
 		mapping_set_error(mapping, error);
 	unlock_page(page);