struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry,
		struct dentry *new_dir, const char *new_name)
{
	int error;
	struct dentry *dentry = NULL, *trap;
	const char *old_name;

	trap = lock_rename(new_dir, old_dir);
	/* Source or destination directories don't exist? */
	if (d_really_is_negative(old_dir) || d_really_is_negative(new_dir))
		goto exit;
	/* Source does not exist, cyclic rename, or mountpoint? */
	if (d_really_is_negative(old_dentry) || old_dentry == trap ||
	    d_mountpoint(old_dentry))
		goto exit;
	dentry = lookup_one_len(new_name, new_dir, strlen(new_name));
	/* Lookup failed, cyclic rename or target exists? */
	if (IS_ERR(dentry) || dentry == trap || d_really_is_positive(dentry))
		goto exit;

	old_name = fsnotify_oldname_init(old_dentry->d_name.name);

	error = simple_rename(d_inode(old_dir), old_dentry, d_inode(new_dir),
			      dentry, 0);
	if (error) {
		fsnotify_oldname_free(old_name);
		goto exit;
	}
	d_move(old_dentry, dentry);
	fsnotify_move(d_inode(old_dir), d_inode(new_dir), old_name,
		d_is_dir(old_dentry),
		NULL, old_dentry);
	fsnotify_oldname_free(old_name);
	unlock_rename(new_dir, old_dir);
	dput(dentry);
	return old_dentry;
exit:
	if (dentry && !IS_ERR(dentry))
		dput(dentry);
	unlock_rename(new_dir, old_dir);
	return NULL;
}
The program contains a code sequence that can run concurrently with other code, and the code sequence 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 that is operating concurrently.