mm: use swp_offset as key in shmem_replace_page()

We changed the key of swap cache tree from swp_entry_t.val to
swp_offset.  We need to do so in shmem_replace_page() as well.

Hugh said:
 "shmem_replace_page() has been wrong since the day I wrote it: good
  enough to work on swap "type" 0, which is all most people ever use
  (especially those few who need shmem_replace_page() at all), but
  broken once there are any non-0 swp_type bits set in the higher order
  bits"

Link: http://lkml.kernel.org/r/20181121215442.138545-1-yuzhao@google.com
Fixes: f6ab1f7f6b2d ("mm, swap: use offset of swap entry as key of swap cache")
Signed-off-by: Yu Zhao <yuzhao@google.com>
Reviewed-by: Matthew Wilcox <willy@infradead.org>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>	[4.9+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/shmem.c b/mm/shmem.c
index d44991e..42b7097 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1509,11 +1509,13 @@ static int shmem_replace_page(struct page **pagep, gfp_t gfp,
 {
        struct page *oldpage, *newpage;
        struct address_space *swap_mapping;
+       swp_entry_t entry;
        pgoff_t swap_index;
        int error;
 
        oldpage = *pagep;
-       swap_index = page_private(oldpage);
+       entry.val = page_private(oldpage);
+       swap_index = swp_offset(entry);
        swap_mapping = page_mapping(oldpage);
 
        /*
@@ -1532,7 +1534,7 @@ static int shmem_replace_page(struct page **pagep, gfp_t gfp,
        __SetPageLocked(newpage);
        __SetPageSwapBacked(newpage);
        SetPageUptodate(newpage);
-       set_page_private(newpage, swap_index);
+       set_page_private(newpage, entry.val);
        SetPageSwapCache(newpage);
 
        /*