swap: prevent reuse during hibernation

[net-next-2.6.git] / mm / swapfile.c

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 03aa2d55f1a2f54fc5eb17b099806edbc83a4049..ed5151079f59437bf54f540d71336ec18a8d76d0 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -686,6 +686,24 @@ int try_to_free_swap(struct page *page)
        if (page_swapcount(page))
                return 0;
 
+       /*
+        * Once hibernation has begun to create its image of memory,
+        * there's a danger that one of the calls to try_to_free_swap()
+        * - most probably a call from __try_to_reclaim_swap() while
+        * hibernation is allocating its own swap pages for the image,
+        * but conceivably even a call from memory reclaim - will free
+        * the swap from a page which has already been recorded in the
+        * image as a clean swapcache page, and then reuse its swap for
+        * another page of the image.  On waking from hibernation, the
+        * original page might be freed under memory pressure, then
+        * later read back in from swap, now with the wrong data.
+        *
+        * Hibernation clears bits from gfp_allowed_mask to prevent
+        * memory reclaim from writing to disk, so check that here.
+        */
+       if (!(gfp_allowed_mask & __GFP_IO))
+               return 0;
+
        delete_from_swap_cache(page);
        SetPageDirty(page);
        return 1;