lockless next_positive()

				    struct list_head *from,

				    int count)

{

	struct dentry *res = NULL;

	unsigned *seq = &parent->d_inode->i_dir_seq, n;

	struct dentry *res;

	struct list_head *p;

	bool skipped;

	int i;

	spin_lock(&parent->d_lock);

retry:

	i = count;

	skipped = false;

	n = smp_load_acquire(seq) & ~1;

	res = NULL;

	rcu_read_lock();

	for (p = from->next; p != &parent->d_subdirs; p = p->next) {

		struct dentry *d = list_entry(p, struct dentry, d_child);

		if (simple_positive(d) && !--count) {

		if (!simple_positive(d)) {

			skipped = true;

		} else if (!--i) {

			res = d;

			break;

		}

	}

	spin_unlock(&parent->d_lock);

	rcu_read_unlock();

	if (skipped) {

		smp_rmb();

		if (unlikely(*seq != n))

			goto retry;

	}

	return res;

}

static void move_cursor(struct dentry *cursor, struct list_head *after)

{

	struct dentry *parent = cursor->d_parent;

	unsigned n, *seq = &parent->d_inode->i_dir_seq;

	spin_lock(&parent->d_lock);

	for (;;) {

		n = *seq;

		if (!(n & 1) && cmpxchg(seq, n, n + 1) == n)

			break;

		cpu_relax();

	}

	__list_del(cursor->d_child.prev, cursor->d_child.next);

	if (after)

		list_add(&cursor->d_child, after);

	else

		list_add_tail(&cursor->d_child, &parent->d_subdirs);

	smp_store_release(seq, n + 2);

	spin_unlock(&parent->d_lock);

}