calculate-superblock-checksum-after-update-free-blocks-inodes

   1 ext4: recalucate superblock checksum after updating free blocks/inodes
   2
   3 When mounting the superblock, ext4_fill_super() calculates the free
   4 blocks and free inodes and stores them in the superblock.  It's not
   5 strictly necessary, since we don't use them any more, but it's nice to
   6 keep them roughly aligned to reality.
   7
   8 Since it's not critical for file system correctness, the code doesn't
   9 call ext4_commit_super().  The problem is that it's in
  10 ext4_commit_super() that we recalculate the superblock checksum.  So
  11 if we're not going to call ext4_commit_super(), we need to call
  12 ext4_superblock_csum_set() to make sure the superblock checksum is
  13 consistent.
  14
  15 Most of the time, this doesn't matter, since we end up calling
  16 ext4_commit_super() very soon thereafter, and definitely by the time
  17 the file system is unmounted.  However, it doesn't work in this
  18 sequence:
  19
  20 mke2fs -Fq -t ext4 /dev/vdc 128M
  21 mount /dev/vdc /vdc
  22 cp xfstests/git-versions /vdc
  23 godown /vdc
  24 umount /vdc
  25 mount /dev/vdc
  26 tune2fs -l /dev/vdc
  27
  28 With this commit, the "tune2fs -l" no longer fails.
  29
  30 Reported-by: Chengguang Xu <cgxu519@gmx.com>
  31 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  32 Cc: stable@vger.kernel.org
  33
  34
  35
  36 ---
  37  fs/ext4/super.c | 2 ++
  38  1 file changed, 2 insertions(+)
  39
  40 diff --git a/fs/ext4/super.c b/fs/ext4/super.c
  41 index f7750bc5b85a..e41da553b430 100644
  42 --- a/fs/ext4/super.c
  43 +++ b/fs/ext4/super.c
  44 @@ -4378,11 +4378,13 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
  45         block = ext4_count_free_clusters(sb);
  46         ext4_free_blocks_count_set(sbi->s_es,
  47                                    EXT4_C2B(sbi, block));
  48 +       ext4_superblock_csum_set(sb);
  49         err = percpu_counter_init(&sbi->s_freeclusters_counter, block,
  50                                   GFP_KERNEL);
  51         if (!err) {
  52                 unsigned long freei = ext4_count_free_inodes(sb);
  53                 sbi->s_es->s_free_inodes_count = cpu_to_le32(freei);
  54 +               ext4_superblock_csum_set(sb);
  55                 err = percpu_counter_init(&sbi->s_freeinodes_counter, freei,
  56                                           GFP_KERNEL);
  57         }