Re: [PATCH v2 18/33] mnt: support ns lookup

[Al Viro <viro@zeniv.linux.org.uk>]

On Fri, Sep 12, 2025 at 01:52:41PM +0200, Christian Brauner wrote:
> Move the mount namespace to the generic ns lookup infrastructure.
> This allows us to drop a bunch of members from struct mnt_namespace.

>  static void mnt_ns_tree_remove(struct mnt_namespace *ns)
>  {
>  	/* remove from global mount namespace list */
> -	if (!is_anon_ns(ns)) {
> -		mnt_ns_tree_write_lock();
> -		rb_erase(&ns->mnt_ns_tree_node, &mnt_ns_tree);
> -		list_bidir_del_rcu(&ns->mnt_ns_list);
> -		mnt_ns_tree_write_unlock();
> -	}
> -
> -	call_rcu(&ns->mnt_ns_rcu, mnt_ns_release_rcu);
> -}
> -
> -static int mnt_ns_find(const void *key, const struct rb_node *node)
> -{
> -	const u64 mnt_ns_id = *(u64 *)key;
> -	const struct mnt_namespace *ns = node_to_mnt_ns(node);
> +	if (!is_anon_ns(ns))
> +		ns_tree_remove(ns);

Conflicts with "mnt_ns_tree_remove(): DTRT if mnt_ns had never been
added to mnt_ns_list".

FWIW, the right thing to do here is

	if (!RB_EMPTY_NODE(to_ns_common(ns)->ns_tree_node))
		ns_tree_remove(ns);