[PATCH] invalidate_complete_page() race fix

If a CPU faults this page into pagetables after invalidate_mapping_pages()
checked page_mapped(), invalidate_complete_page() will still proceed to remove
the page from pagecache.  This leaves the page-faulting process with a
detached page.  If it was MAP_SHARED then file data loss will ensue.

Fix that up by checking the page's refcount after taking tree_lock.

Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 7 insertions, 4 deletions

diff --git a/mm/truncate.c b/mm/truncate.c
index cf1b015df4a7..c6ab55ec6883 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -68,10 +68,10 @@ invalidate_complete_page(struct address_space *mapping, struct page *page)
                 return 0;
 
         write_lock_irq(&mapping->tree_lock);
-        if (PageDirty(page)) {
-                write_unlock_irq(&mapping->tree_lock);
-                return 0;
-        }
+        if (PageDirty(page))
+                goto failed;
+        if (page_count(page) != 2)      /* caller's ref + pagecache ref */
+                goto failed;
 
         BUG_ON(PagePrivate(page));
         __remove_from_page_cache(page);
@@ -79,6 +79,9 @@ invalidate_complete_page(struct address_space *mapping, struct page *page)
         ClearPageUptodate(page);
         page_cache_release(page);       /* pagecache ref */
         return 1;
+failed:
+        write_unlock_irq(&mapping->tree_lock);
+        return 0;
 }
 
 /**