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>
Subject: Re: [PATCH v1] kthread/smpboot: Serialize kthread parking against wakeup
Date: Thu, 26 Apr 2018 11:14:49 +0200 [thread overview]
Message-ID: <20180426091449.GA4082@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <f18c42e4-ead7-fbcd-b7da-6677e8485be9@codeaurora.org>
On Thu, Apr 26, 2018 at 09:34:36AM +0530, Kohli, Gaurav wrote:
> On 4/26/2018 1:39 AM, Peter Zijlstra wrote:
>
> > On Wed, Apr 25, 2018 at 02:03:19PM +0530, Gaurav Kohli wrote:
> > > diff --git a/kernel/smpboot.c b/kernel/smpboot.c
> > > index 5043e74..c5c5184 100644
> > > --- a/kernel/smpboot.c
> > > +++ b/kernel/smpboot.c
> > > @@ -122,7 +122,45 @@ static int smpboot_thread_fn(void *data)
> > > }
> > > if (kthread_should_park()) {
> > > + /*
> > > + * Serialize against wakeup.
> > *
> > * Prior wakeups must complete and later wakeups
> > * will observe TASK_RUNNING.
> > *
> > * This avoids the case where the TASK_RUNNING
> > * store from ttwu() competes with the
> > * TASK_PARKED store from kthread_parkme().
> > *
> > * If the TASK_PARKED store looses that
> > * competition, kthread_unpark() will go wobbly.
> > > + */
> > > + raw_spin_lock(¤t->pi_lock);
> > > __set_current_state(TASK_RUNNING);
> > > + raw_spin_unlock(¤t->pi_lock);
> > > preempt_enable();
> > > if (ht->park && td->status == HP_THREAD_ACTIVE) {
> > > BUG_ON(td->cpu != smp_processor_id());
> > Does that work for you?
>
> We have given patch for testing, usually it takes around 2-3 days for
> reproduction(we will update for the same).
I only changed the comment; surely your compiler doesn't generate
different code for that?
I was asking if the proposed comment was good with you; but see my more
recent email, that actually proposes a different fix.
> > /*
> > * A similar race is possible here, but loosing
> > * the TASK_INTERRUPTIBLE store is harmless and
> > * will make us go around the loop once more.
> > */
>
> Actually instead of race, i am seeing wakeup miss problem which is
> very rare, if we take case of hotplug thread
Yes, triggering these issues is tricky, no doubt about that.
> > And of course, I suspect we actually want to use TASK_IDLE, smpboot
> > threads don't want signals do they? But that probably ought to be a
> > separate patch.
>
> Yes I agree, we can control race from here as well, Please suggest
> would below change be any help here:
That is not what I suggested. I said the thing should use TASK_IDLE
instead of TASK_INTERRUPTIBLE. Not change the location of it.
next prev parent reply other threads:[~2018-04-26 9:14 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 [this message]
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
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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