From: Oleg Nesterov <oleg@redhat.com>
To: "Kohli, Gaurav" <gkohli@codeaurora.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
tglx@linutronix.de, mpe@ellerman.id.au, mingo@kernel.org,
bigeasy@linutronix.de, linux-kernel@vger.kernel.org,
linux-arm-msm@vger.kernel.org,
Neeraj Upadhyay <neeraju@codeaurora.org>,
Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH v1] kthread/smpboot: Serialize kthread parking against wakeup
Date: Tue, 5 Jun 2018 17:08:41 +0200 [thread overview]
Message-ID: <20180605150841.GA24053@redhat.com> (raw)
In-Reply-To: <ba12bc49-33c0-b4ee-05cf-f84124bd66cc@codeaurora.org>
I have to admit that I didn't try to follow this discussion, somehow I thought
that the plan was to use set_special_state(PARKED)...
On 06/05, Kohli, Gaurav wrote:
>
> As last mentioned on mail, we are still seeing issue with the latest
> approach and below is the susceptible race as mentioned earlier..
> controller Thread CPUHP Thread
> takedown_cpu
> kthread_park
> kthread_parkme
> Set KTHREAD_SHOULD_PARK
> smpboot_thread_fn
> set Task interruptible
>
>
> wake_up_process
> if (!(p->state & state))
> goto out;
>
> Kthread_parkme
> SET TASK_PARKED
> schedule
> raw_spin_lock(&rq->lock)
> ttwu_remote
> waiting for __task_rq_lock
> context_switch
>
> finish_lock_switch
>
>
>
> Case TASK_PARKED
> kthread_park_complete
>
>
> SET Running
I think you are right.
And, now that I look at 85f1abe0019fcb3ea10df7029056cf42702283a8
("kthread, sched/wait: Fix kthread_parkme() completion issue") I see this note
int the changelog:
The alternative is to promote TASK_PARKED to a special state, this
guarantees wait_task_inactive() cannot observe a 'stale' TASK_RUNNING
and we'll end up doing the right thing, but this preserves the whole
icky business of potentially migating the still runnable thing.
OK, but __kthread_parkme() can be preempted before it calls schedule(), so the
caller still can be migrated? Plus kthread_park_complete() can be called twice.
No?
Oleg.
next prev parent reply other threads:[~2018-06-05 15:08 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-25 8:33 [PATCH v1] kthread/smpboot: Serialize kthread parking against wakeup Gaurav Kohli
2018-04-25 20:09 ` Peter Zijlstra
2018-04-26 4:04 ` Kohli, Gaurav
2018-04-26 9:14 ` Peter Zijlstra
2018-04-26 8:41 ` Peter Zijlstra
2018-04-26 8:57 ` Peter Zijlstra
2018-04-26 15:53 ` Kohli, Gaurav
2018-04-30 11:17 ` Peter Zijlstra
2018-05-01 7:50 ` Kohli, Gaurav
2018-05-01 10:18 ` Peter Zijlstra
2018-05-01 10:40 ` Peter Zijlstra
2018-05-01 10:40 ` Kohli, Gaurav
2018-05-01 11:31 ` Peter Zijlstra
2018-05-01 11:46 ` Kohli, Gaurav
2018-05-01 13:19 ` Peter Zijlstra
2018-05-02 5:15 ` Kohli, Gaurav
2018-05-02 8:20 ` Peter Zijlstra
2018-05-02 10:13 ` Kohli, Gaurav
2018-05-07 11:09 ` Kohli, Gaurav
2018-05-07 11:23 ` Kohli, Gaurav
2018-06-05 11:13 ` Kohli, Gaurav
2018-06-05 15:08 ` Oleg Nesterov [this message]
2018-06-05 15:22 ` Peter Zijlstra
2018-06-05 15:40 ` Peter Zijlstra
2018-06-05 16:35 ` Oleg Nesterov
2018-06-05 18:21 ` Kohli, Gaurav
2018-06-05 20:13 ` Peter Zijlstra
2018-06-06 13:51 ` Oleg Nesterov
2018-06-06 15:03 ` Peter Zijlstra
2018-06-06 15:04 ` Peter Zijlstra
2018-06-06 15:22 ` Peter Zijlstra
2018-06-06 18:59 ` Peter Zijlstra
2018-06-07 8:30 ` Kohli, Gaurav
2018-05-01 10:44 ` Peter Zijlstra
2018-04-26 16:02 ` Andrea Parri
2018-04-26 16:18 ` Oleg Nesterov
2018-04-30 11:20 ` Peter Zijlstra
2018-04-30 11:56 ` Peter Zijlstra
2018-04-28 6:43 ` [lkp-robot] [kthread/smpboot] cad8e99675: inconsistent{IN-HARDIRQ-W}->{HARDIRQ-ON-W}usage kernel test robot
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