Re: [PATCH 4/6] make struct mountpoint bear the dentry reference to mountpoint, not struct mount

[Linus Torvalds]

On Sun, Jul 7, 2019 at 2:40 PM Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
>
> It is namespace_sem.  Of all put_mountpoint() callers only the one
> from mntput_no_expire() (disposing of stuck MNT_LOCKed children)
> is not under namespace_sem;
>
>                 list_for_each_entry_safe(p, tmp, &mnt->mnt_mounts,  mnt_child) {
> -                       umount_mnt(p);
> +                       umount_mnt(p, &list);
>                 }
> in mntput_no_expire() passes a local list to umount_mnt() (which passes it
> to put_mountpoint()).

Ahh. Ok. This would be better with a comment. Maybe a separate helper
function with that comment and the special case of passing in NULL (or
maybe not pass in NULL at all, but pass in ex_mountpoints?).

Different locking requirements depending on argument values is very
confusing and easily overlooked..

                Linus