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From: Peter Zijlstra <peterz@infradead.org>
To: "Kohli, Gaurav" <gkohli@codeaurora.org>
Cc: 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>,
	Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH v1] kthread/smpboot: Serialize kthread parking against wakeup
Date: Tue, 1 May 2018 12:40:15 +0200	[thread overview]
Message-ID: <20180501104015.GE12235@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180501101845.GE12217@hirez.programming.kicks-ass.net>

On Tue, May 01, 2018 at 12:18:45PM +0200, Peter Zijlstra wrote:
> Aaaah... I think I've spotted a problem there. We clear SHOULD_PARK
> before we rebind, so if the thread lost the first PARKED store,
> does the completion, gets migrated, cycles through the loop and now
> observes !SHOULD_PARK and bails the wait-loop, then __kthread_bind()
> will forever wait.
> 
> Is that what you had in mind?

Another possible problem is concurrent thread_park(), if both observe
!IS_PARKED, we'll end up with 2 threads waiting on the completion, but
we only do a single complete().

Of course, this might not be a suppored use of the API, and I don't
think this will ever actually happen. But the whole !test_bit(IS_PARKED)
thing seems to suggest it is fine calling this on an already parked
thread.

Confusing stuff that should be cleared up in any case.

  reply	other threads:[~2018-05-01 10:40 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 [this message]
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
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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