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Date: Mon, 23 Jan 2017 13:52:23 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>,
        Kees Cook <keescook@chromium.org>
Cc: Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Cyrill Gorcunov <gorcunov@openvz.org>,
        John Stultz <john.stultz@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Nicolas Pitre <nicolas.pitre@linaro.org>,
        Michal Hocko <mhocko@suse.com>,
        Stanislav Kinsburskiy <skinsbursky@virtuozzo.com>,
        Mateusz Guzik <mguzik@redhat.com>, linux-kernel@vger.kernel.org,
        Pavel Emelyanov <xemul@virtuozzo.com>,
        Konstantin Khorenko <khorenko@virtuozzo.com>
Subject: task_is_descendant() cleanup
Message-ID: <20170123125222.GA28626@redhat.com>
References: <20170119164346.4214-1-ptikhomirov@virtuozzo.com>
 <20170120181359.GA17205@redhat.com>
 <4908be49-d3c3-366d-0fd1-05249ef4ecef@virtuozzo.com>
 <20170123115534.GA11827@redhat.com>
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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.