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    Subject[PATCH 3.16 037/136] btrfs: avoid null pointer dereference on fs_info when calling btrfs_crit
    3.16.54-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Colin Ian King <colin.king@canonical.com>

    commit 3993b112dac968612b0b213ed59cb30f50b0015b upstream.

    There are checks on fs_info in __btrfs_panic to avoid dereferencing a
    null fs_info, however, there is a call to btrfs_crit that may also
    dereference a null fs_info. Fix this by adding a check to see if fs_info
    is null and only print the s_id if fs_info is non-null.

    Detected by CoverityScan CID#401973 ("Dereference after null check")

    Fixes: efe120a067c8 ("Btrfs: convert printk to btrfs_ and fix BTRFS prefix")
    Signed-off-by: Colin Ian King <colin.king@canonical.com>
    Reviewed-by: David Sterba <dsterba@suse.com>
    Signed-off-by: David Sterba <dsterba@suse.com>
    [bwh: Backported to 3.16: adjust context]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    fs/btrfs/super.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- a/fs/btrfs/super.c
    +++ b/fs/btrfs/super.c
    @@ -185,7 +185,6 @@ static const char * const logtypes[] = {

    void btrfs_printk(const struct btrfs_fs_info *fs_info, const char *fmt, ...)
    {
    - struct super_block *sb = fs_info->sb;
    char lvl[4];
    struct va_format vaf;
    va_list args;
    @@ -207,7 +206,8 @@ void btrfs_printk(const struct btrfs_fs_
    vaf.fmt = fmt;
    vaf.va = &args;

    - printk("%sBTRFS %s (device %s): %pV\n", lvl, type, sb->s_id, &vaf);
    + printk("%sBTRFS %s (device %s): %pV\n", lvl, type,
    + fs_info ? fs_info->sb->s_id : "<unknown>", &vaf);

    va_end(args);
    }
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