From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: "Kohli, Gaurav" <gkohli@codeaurora.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 17:22:12 +0200 [thread overview]
Message-ID: <20180605152212.GY12180@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180605150841.GA24053@redhat.com>
On Tue, Jun 05, 2018 at 05:08:41PM +0200, Oleg Nesterov wrote:
> 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.
Argh... I forgot TASK_DEAD does the whole thing with preempt_disable().
Let me stare at that a bit.
next prev parent reply other threads:[~2018-06-05 15:22 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
2018-06-05 15:22 ` Peter Zijlstra [this message]
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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