src/patches/suse-2.6.27.31/patches.suse/SoN-fix-sync

   1 References: 441793
   2 Subject: Cope with racy nature of sync_page in swap_sync_page
   3
   4 From: NeilBrown <neilb@suse.de>
   5
   6 sync_page is called without that PageLock held.  This means that,
   7 for example, PageSwapCache can be cleared at any time.
   8 We need to be careful not to put much trust any any part of the page.
   9
  10 So allow page_swap_info to return NULL of the page is no longer
  11 in a SwapCache, and handle the NULL gracefully in swap_sync_page.
  12
  13 No other calls need to handle the NULL as that all hold PageLock,
  14 so PageSwapCache cannot be cleared by surprise.  Add a WARN_ON to
  15 document this fact and help find out if I am wrong.
  16
  17 Acked-By:  Miklos Szeredi <mszeredi@novell.com>
  18 Signed-off-by: NeilBrown <neilb@suse.de>
  19
  20 ---
  21  mm/page_io.c  |    2 ++
  22  mm/swapfile.c |    9 ++++++++-
  23  2 files changed, 10 insertions(+), 1 deletion(-)
  24
  25 --- linux-2.6.27.orig/mm/page_io.c
  26 +++ linux-2.6.27/mm/page_io.c
  27 @@ -139,6 +139,8 @@ void swap_sync_page(struct page *page)
  28  {
  29         struct swap_info_struct *sis = page_swap_info(page);
  30
  31 +       if (!sis)
  32 +               return;
  33         if (sis->flags & SWP_FILE) {
  34                 struct address_space *mapping = sis->swap_file->f_mapping;
  35
  36 --- linux-2.6.27.orig/mm/swapfile.c
  37 +++ linux-2.6.27/mm/swapfile.c
  38 @@ -1845,7 +1845,13 @@ get_swap_info_struct(unsigned type)
  39  struct swap_info_struct *page_swap_info(struct page *page)
  40  {
  41         swp_entry_t swap = { .val = page_private(page) };
  42 -       BUG_ON(!PageSwapCache(page));
  43 +       if (!PageSwapCache(page) || !swap.val) {
  44 +               /* This should only happen from sync_page.
  45 +                * In other cases the page should be locked and
  46 +                * should be in a SwapCache
  47 +                */
  48 +               return NULL;
  49 +       }
  50         return &swap_info[swp_type(swap)];
  51  }
  52