static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
{
	struct mountpoint *mp;
	struct mount *parent;
	int err;

	mnt_flags &= ~MNT_INTERNAL_FLAGS;

	mp = lock_mount(path);
	if (IS_ERR(mp))
		return PTR_ERR(mp);

	parent = real_mount(path->mnt);
	err = -EINVAL;
	if (unlikely(!check_mnt(parent))) {
		/* that's acceptable only for automounts done in private ns */
		if (!(mnt_flags & MNT_SHRINKABLE))
			goto unlock;
		/* ... and for those we'd better have mountpoint still alive */
		if (!parent->mnt_ns)
			goto unlock;
	}

	/* Refuse the same filesystem on the same mount point */
	err = -EBUSY;
	if (path->mnt->mnt_sb == newmnt->mnt.mnt_sb &&
	    path->mnt->mnt_root == path->dentry)
		goto unlock;

	err = -EINVAL;
	if (d_is_symlink(newmnt->mnt.mnt_root))
		goto unlock;

	newmnt->mnt.mnt_flags = mnt_flags;
	err = graft_tree(newmnt, parent, mp);

unlock:
	unlock_mount(mp);
	return err;
}
static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
{
	struct mountpoint *mp;
	struct mount *parent;
	int err;

	mnt_flags &= ~MNT_INTERNAL_FLAGS;

	mp = lock_mount(path);
	if (IS_ERR(mp))
		return PTR_ERR(mp);

	parent = real_mount(path->mnt);
	err = -EINVAL;
	if (unlikely(!check_mnt(parent))) {
		 
		if (!(mnt_flags & MNT_SHRINKABLE))
			goto unlock;
		 
		if (!parent->mnt_ns)
			goto unlock;
	}

	 
	err = -EBUSY;
	if (path->mnt->mnt_sb == newmnt->mnt.mnt_sb &&
	    path->mnt->mnt_root == path->dentry)
		goto unlock;

	err = -EINVAL;
	if (d_is_symlink(newmnt->mnt.mnt_root))
		goto unlock;

	newmnt->mnt.mnt_flags = mnt_flags;
	err = graft_tree(newmnt, parent, mp);

unlock:
	unlock_mount(mp);
	return err;
}