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    Subject[PATCH 3.16 046/366] ext4: do not update s_last_mounted of a frozen fs
    3.16.61-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Amir Goldstein <amir73il@gmail.com>

    commit db6516a5e7ddb6dc72d167b920f2f272596ea22d upstream.

    If fs is frozen after mount and before the first file open, the
    update of s_last_mounted bypasses freeze protection and prints out
    a WARNING splat:

    $ mount /vdf
    $ fsfreeze -f /vdf
    $ cat /vdf/foo

    [ 31.578555] WARNING: CPU: 1 PID: 1415 at
    fs/ext4/ext4_jbd2.c:53 ext4_journal_check_start+0x48/0x82

    [ 31.614016] Call Trace:
    [ 31.614997] __ext4_journal_start_sb+0xe4/0x1a4
    [ 31.616771] ? ext4_file_open+0xb6/0x189
    [ 31.618094] ext4_file_open+0xb6/0x189

    If fs is frozen, skip s_last_mounted update.

    [backport hint: to apply to stable tree, need to apply also patches
    vfs: add the sb_start_intwrite_trylock() helper
    ext4: factor out helper ext4_sample_last_mounted()]

    Fixes: bc0b0d6d69ee ("ext4: update the s_last_mounted field in the superblock")
    Signed-off-by: Amir Goldstein <amir73il@gmail.com>
    Signed-off-by: Theodore Ts'o <tytso@mit.edu>
    Reviewed-by: Jan Kara <jack@suse.cz>
    [bwh: Backported to 3.16: adjust context]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    fs/ext4/file.c | 14 +++++++++-----
    1 file changed, 9 insertions(+), 5 deletions(-)

    --- a/fs/ext4/file.c
    +++ b/fs/ext4/file.c
    @@ -220,7 +220,7 @@ static int ext4_sample_last_mounted(stru
    if (likely(sbi->s_mount_flags & EXT4_MF_MNTDIR_SAMPLED))
    return 0;

    - if (sb->s_flags & MS_RDONLY)
    + if (sb->s_flags & MS_RDONLY || !sb_start_intwrite_trylock(sb))
    return 0;

    sbi->s_mount_flags |= EXT4_MF_MNTDIR_SAMPLED;
    @@ -234,21 +234,25 @@ static int ext4_sample_last_mounted(stru
    path.mnt = mnt;
    path.dentry = mnt->mnt_root;
    cp = d_path(&path, buf, sizeof(buf));
    + err = 0;
    if (IS_ERR(cp))
    - return 0;
    + goto out;

    handle = ext4_journal_start_sb(sb, EXT4_HT_MISC, 1);
    + err = PTR_ERR(handle);
    if (IS_ERR(handle))
    - return PTR_ERR(handle);
    + goto out;
    BUFFER_TRACE(sbi->s_sbh, "get_write_access");
    err = ext4_journal_get_write_access(handle, sbi->s_sbh);
    if (err)
    - goto out;
    + goto out_journal;
    strlcpy(sbi->s_es->s_last_mounted, cp,
    sizeof(sbi->s_es->s_last_mounted));
    ext4_handle_dirty_super(handle, sb);
    -out:
    +out_journal:
    ext4_journal_stop(handle);
    +out:
    + sb_end_intwrite(sb);
    return err;
    }

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