From: Peter Zijlstra <peterz@infradead.org>
To: Kirill Tkhai <tkhai@yandex.ru>
Cc: linux-kernel@vger.kernel.org, Kirill Tkhai <ktkhai@parallels.com>,
Ingo Molnar <mingo@redhat.com>, Juri Lelli <juri.lelli@gmail.com>
Subject: Re: [PATCH v2 1/3] sched/dl: Implement cancel_dl_timer() to use in switched_from_dl()
Date: Thu, 2 Oct 2014 11:34:08 +0200 [thread overview]
Message-ID: <20141002093408.GB2849@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20140930210412.5258.35299.stgit@localhost>
On Wed, Oct 01, 2014 at 01:04:22AM +0400, Kirill Tkhai wrote:
> From: Kirill Tkhai <ktkhai@parallels.com>
>
> hrtimer_try_to_cancel() may bring a suprise, its call may fail.
Well, not really a surprise that, its a _try_ operation after all.
> raw_spin_lock(&rq->lock)
> ... dl_task_timer raw_spin_lock(&rq->lock)
> ... raw_spin_lock(&rq->lock) ...
> switched_from_dl() ... ...
> hrtimer_try_to_cancel() ... ...
> switched_to_fair() ... ...
> ... ... ...
> ... ... ...
> raw_spin_unlock(&rq->lock) ... (asquired)
> ... ... ...
> ... ... ...
> do_exit() ... ...
> schedule() ... ...
> raw_spin_lock(&rq->lock) ... raw_spin_unlock(&rq->lock)
> ... ... ...
> raw_spin_unlock(&rq->lock) ... raw_spin_lock(&rq->lock)
> ... ... (asquired)
> put_task_struct() ... ...
> free_task_struct() ... ...
> ... ... raw_spin_unlock(&rq->lock)
> ... (asquired) ...
> ... ... ...
> ... Surprise!!! ...
>
> So, let's implement 100% guaranteed way to cancel the timer and let's
> be sure we are safe even in very unlikely situations.
>
> We do not create any problem with rq unlocking, because it already
> may happed below in pull_dl_task(). No problem with deadline tasks
> balancing too.
That doesn't sound right. pull_dl_task() is an entirely different
callchain than switched_from(). Now it might still be fine, but you
cannot compare it with pull_dl_task.
next prev parent reply other threads:[~2014-10-02 9:34 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-30 21:04 [PATCH v2 1/3] sched/dl: Implement cancel_dl_timer() to use in switched_from_dl() Kirill Tkhai
2014-09-30 21:04 ` [PATCH v2 2/3] sched/dl: Cleanup prio_changed_dl() Kirill Tkhai
2014-10-02 9:36 ` Peter Zijlstra
2014-10-02 9:52 ` Kirill Tkhai
2014-10-21 16:24 ` Juri Lelli
2014-10-21 16:33 ` Kirill Tkhai
2014-10-22 9:33 ` Juri Lelli
2014-10-23 23:04 ` Wanpeng Li
2014-10-24 9:26 ` Juri Lelli
2014-09-30 21:04 ` [PATCH v2 3/3] sched/fair: Delete resched_cpu() from idle_balance() Kirill Tkhai
2014-10-03 5:28 ` [tip:sched/core] " tip-bot for Kirill Tkhai
2014-10-02 9:34 ` Peter Zijlstra [this message]
2014-10-02 10:05 ` [PATCH v2 1/3] sched/dl: Implement cancel_dl_timer() to use in switched_from_dl() Kirill Tkhai
2014-10-21 10:30 ` Juri Lelli
2014-10-21 10:48 ` Kirill Tkhai
2014-10-21 11:41 ` Juri Lelli
2014-10-21 14:21 ` Kirill Tkhai
2014-10-22 10:00 ` Juri Lelli
2014-10-23 8:39 ` Kirill Tkhai
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