SYSCALL_DEFINE3(get_robust_list, int, pid,
		struct robust_list_head __user * __user *, head_ptr,
		size_t __user *, len_ptr)
{
	struct robust_list_head __user *head;
	unsigned long ret;
	struct task_struct *p;

	if (!futex_cmpxchg_enabled)
		return -ENOSYS;

	rcu_read_lock();

	ret = -ESRCH;
	if (!pid)
		p = current;
	else {
		p = find_task_by_vpid(pid);
		if (!p)
			goto err_unlock;
	}

	ret = -EPERM;
	if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
		goto err_unlock;

	head = p->robust_list;
	rcu_read_unlock();

	if (put_user(sizeof(*head), len_ptr))
		return -EFAULT;
	return put_user(head, head_ptr);

err_unlock:
	rcu_read_unlock();

	return ret;
}
Unknown