releases/2.6.31.8/0050-ext4-fix-a-BUG_ON-crash-by-checking-that-page-has-bu.patch

   1 From 7fcfa625f4bdba955d0fb0b717dc576b1e48b470 Mon Sep 17 00:00:00 2001
   2 From: Theodore Ts'o <tytso@mit.edu>
   3 Date: Wed, 30 Sep 2009 22:57:41 -0400
   4 Subject: [PATCH 50/85] ext4: fix a BUG_ON crash by checking that page has buffers attached to it
   5
   6 (cherry picked from commit 1f94533d9cd75f6d2826018d54a971b9cc085992)
   7
   8 In ext4_num_dirty_pages() we were calling page_buffers() before
   9 checking to see if the page actually had pages attached to it; this
  10 would cause a BUG check crash in the inline function page_buffers().
  11
  12 Thanks to Markus Trippelsdorf for reporting this bug.
  13
  14 Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
  15 Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
  16 ---
  17  fs/ext4/inode.c |   22 +++++++++++-----------
  18  1 file changed, 11 insertions(+), 11 deletions(-)
  19
  20 --- a/fs/ext4/inode.c
  21 +++ b/fs/ext4/inode.c
  22 @@ -1147,8 +1147,8 @@ static int check_block_validity(struct i
  23  }
  24
  25  /*
  26 - * Return the number of dirty pages in the given inode starting at
  27 - * page frame idx.
  28 + * Return the number of contiguous dirty pages in a given inode
  29 + * starting at page frame idx.
  30   */
  31  static pgoff_t ext4_num_dirty_pages(struct inode *inode, pgoff_t idx,
  32                                     unsigned int max_pages)
  33 @@ -1182,15 +1182,15 @@ static pgoff_t ext4_num_dirty_pages(stru
  34                                 unlock_page(page);
  35                                 break;
  36                         }
  37 -                       head = page_buffers(page);
  38 -                       bh = head;
  39 -                       do {
  40 -                               if (!buffer_delay(bh) &&
  41 -                                   !buffer_unwritten(bh)) {
  42 -                                       done = 1;
  43 -                                       break;
  44 -                               }
  45 -                       } while ((bh = bh->b_this_page) != head);
  46 +                       if (page_has_buffers(page)) {
  47 +                               bh = head = page_buffers(page);
  48 +                               do {
  49 +                                       if (!buffer_delay(bh) &&
  50 +                                           !buffer_unwritten(bh))
  51 +                                               done = 1;
  52 +                                       bh = bh->b_this_page;
  53 +                               } while (!done && (bh != head));
  54 +                       }
  55                         unlock_page(page);
  56                         if (done)
  57                                 break;