do-not-update-s_last_mounted-of-a-frozen-fs

   1 ext4: do not update s_last_mounted of a frozen fs
   2
   3 From: Amir Goldstein <amir73il@gmail.com>
   4
   5 If fs is frozen after mount and before the first file open, the
   6 update of s_last_mounted bypasses freeze protection and prints out
   7 a WARNING splat:
   8
   9 $ mount /vdf
  10 $ fsfreeze -f /vdf
  11 $ cat /vdf/foo
  12
  13 [   31.578555] WARNING: CPU: 1 PID: 1415 at
  14 fs/ext4/ext4_jbd2.c:53 ext4_journal_check_start+0x48/0x82
  15
  16 [   31.614016] Call Trace:
  17 [   31.614997]  __ext4_journal_start_sb+0xe4/0x1a4
  18 [   31.616771]  ? ext4_file_open+0xb6/0x189
  19 [   31.618094]  ext4_file_open+0xb6/0x189
  20
  21 If fs is frozen, skip s_last_mounted update.
  22
  23 [backport hint: to apply to stable tree, need to apply also patches
  24  vfs: add the sb_start_intwrite_trylock() helper
  25  ext4: factor out helper ext4_sample_last_mounted()]
  26
  27 Cc: stable@vger.kernel.org
  28 Fixes: bc0b0d6d69ee ("ext4: update the s_last_mounted field in the superblock")
  29 Signed-off-by: Amir Goldstein <amir73il@gmail.com>
  30 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  31 Reviewed-by: Jan Kara <jack@suse.cz>
  32 ---
  33  fs/ext4/file.c | 14 +++++++++-----
  34  1 file changed, 9 insertions(+), 5 deletions(-)
  35
  36 diff --git a/fs/ext4/file.c b/fs/ext4/file.c
  37 index 065e95bb7186..918a59b6bc1a 100644
  38 --- a/fs/ext4/file.c
  39 +++ b/fs/ext4/file.c
  40 @@ -392,7 +392,7 @@ static int ext4_sample_last_mounted(struct super_block *sb,
  41         if (likely(sbi->s_mount_flags & EXT4_MF_MNTDIR_SAMPLED))
  42                 return 0;
  43
  44 -       if (sb_rdonly(sb))
  45 +       if (sb_rdonly(sb) || !sb_start_intwrite_trylock(sb))
  46                 return 0;
  47
  48         sbi->s_mount_flags |= EXT4_MF_MNTDIR_SAMPLED;
  49 @@ -406,21 +406,25 @@ static int ext4_sample_last_mounted(struct super_block *sb,
  50         path.mnt = mnt;
  51         path.dentry = mnt->mnt_root;
  52         cp = d_path(&path, buf, sizeof(buf));
  53 +       err = 0;
  54         if (IS_ERR(cp))
  55 -               return 0;
  56 +               goto out;
  57
  58         handle = ext4_journal_start_sb(sb, EXT4_HT_MISC, 1);
  59 +       err = PTR_ERR(handle);
  60         if (IS_ERR(handle))
  61 -               return PTR_ERR(handle);
  62 +               goto out;
  63         BUFFER_TRACE(sbi->s_sbh, "get_write_access");
  64         err = ext4_journal_get_write_access(handle, sbi->s_sbh);
  65         if (err)
  66 -               goto out;
  67 +               goto out_journal;
  68         strlcpy(sbi->s_es->s_last_mounted, cp,
  69                 sizeof(sbi->s_es->s_last_mounted));
  70         ext4_handle_dirty_super(handle, sb);
  71 -out:
  72 +out_journal:
  73         ext4_journal_stop(handle);
  74 +out:
  75 +       sb_end_intwrite(sb);
  76         return err;
  77  }
  78
  79 --
  80 2.7.4
  81
  82