task_is_descendant() cleanup

[Oleg Nesterov <oleg@redhat.com>]

On 01/23, Oleg Nesterov wrote:
>
> Btw task_is_descendant() looks wrong at first glance.

No, I missed the 2nd ->group_leader dereference. Still this function looks
overcomplicated and the usage of thread_group_leader/group_leader just add
the unnecessary confusion. It can be simplified a little bit:

	static int task_is_descendant(struct task_struct *parent,
				      struct task_struct *child)
	{
		int rc = 0;
		struct task_struct *walker;

		if (!parent || !child)
			return 0;

		rcu_read_lock();
		for (walker = child; walker->pid; walker = rcu_dereference(walker->real_parent))
			if (same_thread_group(parent, walker)) {
				rc = 1;
				break;
			}
		rcu_read_unlock();

		return rc;
	}

Kees, I can send a patch if you think this very minor cleanup makes any sense.

Oleg.