linux-kernel - Re: [PATCH 1/1] do_exit(): Solve possibility of BUG() due to race with try_to_wake

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Date:	Wed, 03 Sep 2014 13:04:36 +0400
From:	Kirill Tkhai <tkhai@...dex.ru>
To:	Oleg Nesterov <oleg@...hat.com>,
	Kautuk Consul <consul.kautuk@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	David Rientjes <rientjes@...gle.com>,
	Ionut Alexa <ionut.m.alexa@...il.com>,
	Guillaume Morin <guillaume@...infr.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] do_exit(): Solve possibility of BUG() due to race with try_to_wake_up()

25.08.2014, 20:01, "Oleg Nesterov" <oleg@...hat.com>:
> Peter, do you remember another problem with TASK_DEAD we discussed recently?
> (prev_state == TASK_DEAD detection in finish_task_switch() still looks racy).

One more problem with task_dead just to mention it here.

Below is racy with the change of sched_class:

        if (prev->sched_class->task_dead)
                prev->sched_class->task_dead(prev);

switched_from_dl() does not cancel running timers.

So, if dl_task_timer() is slow (it is unhappy with rq->lock acquiring),
the timer is executing when tasks is already dead.

Kirill
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