From: Oleg Nesterov <oleg@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>,
Yasunori Goto <y-goto@jp.fujitsu.com>,
Thomas Gleixner <tglx@linutronix.de>,
Hiroyuki KAMEZAWA <kamezawa.hiroyu@jp.fujitsu.com>,
Motohiro Kosaki <kosaki.motohiro@jp.fujitsu.com>,
Linux Kernel ML <linux-kernel@vger.kernel.org>
Subject: Re: [BUG] TASK_DEAD task is able to be woken up in special condition
Date: Thu, 26 Jan 2012 17:26:11 +0100 [thread overview]
Message-ID: <20120126162611.GA1982@redhat.com> (raw)
In-Reply-To: <1327591943.2446.111.camel@twins>
On 01/26, Peter Zijlstra wrote:
>
> So since we never call schedule() the p->on_rq thing will always be
> true. This means we don't need to consider all the icky ttwu after that,
> it also means the whole thing is inside ->pi_lock.
>
> So we only have to consider the exact case Yasunori-San illustrated, and
> waiting on ->pi_lock is sufficient.
Yes, and this is why I think Yasunori-san's patch should work. Because,
to remind, it adds unlock_wait(pi_lock).
> However I think your proposal:
>
> > for (;;) {
> > tsk->state = TASK_DEAD;
> > schedule();
> > }
>
> should equally work, if we hit the race and call schedule() with ->state
> = TASK_RUNNING,
Yes, in this case everything is fine, but we can shedule() with TASK_DEAD
state. preempt_disable() can't (and shouldn't) prevent deactivate_task().
To simplify, try_to_wake_up() does
spin_lock(pi_lock);
if (!(p->state & state))
goto out;
/* WINDOW */
if (p->on_rq) {
... everything is fine ...
}
p->state = TASK_WAKING;
ttwu_queue(p, cpu);
And the exiting task does
// but do not sleep ...
current->state = TASK_UNINTERRUPTIBLE;
// ttwu() checks ->state
...
tsk->state = TASK_DEAD;
schedule();
-> deactivate_task();
-> tsk->on_rq = 0;
-> finish_task_switch();
// ttwu() checks ->on_rq
In theory it can do this all in the WINDOW above. In this case we
can wake it up again, after finish_task_switch()-put_task_struct().
No?
Oleg.
next prev parent reply other threads:[~2012-01-26 16:32 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-22 0:42 [BUG] TASK_DEAD task is able to be woken up in special condition Yasunori Goto
2011-12-22 2:14 ` KOSAKI Motohiro
2011-12-22 8:22 ` Yasunori Goto
2011-12-22 20:02 ` KOSAKI Motohiro
2011-12-23 9:49 ` Peter Zijlstra
2011-12-23 15:41 ` Oleg Nesterov
2011-12-26 8:23 ` Yasunori Goto
2011-12-26 17:11 ` Oleg Nesterov
2011-12-27 6:48 ` Yasunori Goto
2012-01-06 10:22 ` Yasunori Goto
2012-01-06 11:01 ` Peter Zijlstra
2012-01-06 12:01 ` Yasunori Goto
2012-01-06 12:43 ` Peter Zijlstra
2012-01-06 14:12 ` Oleg Nesterov
2012-01-06 14:19 ` Oleg Nesterov
2012-01-07 1:31 ` Yasunori Goto
2012-01-16 11:51 ` Yasunori Goto
2012-01-16 13:38 ` Peter Zijlstra
2012-01-17 8:40 ` Yasunori Goto
2012-01-17 9:06 ` Ingo Molnar
2012-01-17 15:12 ` Oleg Nesterov
2012-01-18 9:42 ` Ingo Molnar
2012-01-18 14:20 ` Oleg Nesterov
2012-01-24 10:19 ` Peter Zijlstra
2012-01-24 10:55 ` Peter Zijlstra
2012-01-24 17:25 ` KOSAKI Motohiro
2012-01-25 15:45 ` Oleg Nesterov
2012-01-25 16:51 ` Peter Zijlstra
2012-01-25 17:43 ` Oleg Nesterov
2012-01-26 15:32 ` Peter Zijlstra
2012-01-26 16:26 ` Oleg Nesterov [this message]
2012-01-27 8:59 ` Peter Zijlstra
2012-01-24 10:11 ` Peter Zijlstra
2012-01-26 9:39 ` Ingo Molnar
2012-01-28 12:03 ` [tip:sched/core] sched: Fix ancient race in do_exit() tip-bot for Yasunori Goto
2012-01-28 21:12 ` Linus Torvalds
2012-01-29 16:07 ` Oleg Nesterov
2012-01-29 17:44 ` Linus Torvalds
2012-01-29 18:28 ` Linus Torvalds
2012-01-29 18:59 ` Oleg Nesterov
2012-01-30 16:27 ` Linus Torvalds
2012-01-06 13:48 ` [BUG] TASK_DEAD task is able to be woken up in special condition Oleg Nesterov
2011-12-28 21:07 ` KOSAKI Motohiro
2012-01-24 10:23 ` Peter Zijlstra
2012-01-24 18:01 ` KOSAKI Motohiro
2012-01-25 6:15 ` Mike Galbraith
2012-01-26 21:24 ` KOSAKI Motohiro
2012-01-25 10:10 ` Peter Zijlstra
2012-01-26 20:25 ` [tip:sched/urgent] sched: Fix rq->nr_uninterruptible update race tip-bot for Peter Zijlstra
2012-01-27 5:20 ` Rakib Mullick
2012-01-27 8:19 ` Peter Zijlstra
2012-01-27 14:11 ` Rakib Mullick
2012-01-26 21:21 ` [BUG] TASK_DEAD task is able to be woken up in special condition KOSAKI Motohiro
2012-01-27 8:21 ` Peter Zijlstra
2011-12-26 6:52 ` Yasunori Goto
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