struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
{
	if (IS_ERR(inode))
		return ERR_CAST(inode);

	BUG_ON(!d_unhashed(dentry));

	if (!inode)
		goto out;

	security_d_instantiate(dentry, inode);
	spin_lock(&inode->i_lock);
	if (S_ISDIR(inode->i_mode)) {
		struct dentry *new = __d_find_any_alias(inode);
		if (unlikely(new)) {
			/* The reference to new ensures it remains an alias */
			spin_unlock(&inode->i_lock);
			write_seqlock(&rename_lock);
			if (unlikely(d_ancestor(new, dentry))) {
				write_sequnlock(&rename_lock);
				dput(new);
				new = ERR_PTR(-ELOOP);
				pr_warn_ratelimited(
					"VFS: Lookup of '%s' in %s %s"
					" would have caused loop\n",
					dentry->d_name.name,
					inode->i_sb->s_type->name,
					inode->i_sb->s_id);
			} else if (!IS_ROOT(new)) {
				int err = __d_unalias(inode, dentry, new);
				write_sequnlock(&rename_lock);
				if (err) {
					dput(new);
					new = ERR_PTR(err);
				}
			} else {
				__d_move(new, dentry, false);
				write_sequnlock(&rename_lock);
			}
			iput(inode);
			return new;
		}
	}
out:
	__d_add(dentry, inode);
	return NULL;
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.