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    SubjectRe: [PATCH 2.6.24-rc7 2/2] sysfs: fix bugs in sysfs_rename/move_dir()


    On Wed, 16 Jan 2008, Tejun Heo wrote:
    >
    > * sysfs_move_dir() has an extra dput() on success path.

    Are you sure? How did this ever work?

    Also, looking at this, I think the "how did this ever work" question is
    answered by "it didn't", but I also think there are still serious problems
    there. Look at

    again:
    mutex_lock(&old_parent->d_inode->i_mutex);
    if (!mutex_trylock(&new_parent->d_inode->i_mutex)) {
    mutex_unlock(&old_parent->d_inode->i_mutex);
    goto again;
    }

    and wonder what happen sif old_parent == new_parent. Is that trying to
    avoid an ABBA deadlock? Normally you'd do it by ordering the locks, or by
    taking a third lock to guarantee serialization at a higher level (ie the
    "s_vfs_rename_mutex" on the VFS layer)

    I'd like to apply these two patches, but I really want to get more of an
    ack for them from somebody like Al, or at least more of an explanation for
    why it's all the right thing.

    Linus


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