From: Byungchul Park <byungchul.park@lge.com>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: "Paul E. McKenney" <paulmck@linux.ibm.com>,
Byungchul Park <max.byungchul.park@gmail.com>,
rcu <rcu@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
kernel-team@lge.com
Subject: Re: [PATCH] rcu: Make jiffies_till_sched_qs writable
Date: Fri, 19 Jul 2019 10:10:11 +0900 [thread overview]
Message-ID: <20190719011011.GC28226@X58A-UD3R> (raw)
In-Reply-To: <CAEXW_YQij-N2-NFjUQtsmYxVLtWxcQk_Kb16fGBzzPAZtWg+sg@mail.gmail.com>
On Thu, Jul 18, 2019 at 08:52:52PM -0400, Joel Fernandes wrote:
> On Thu, Jul 18, 2019 at 8:40 PM Byungchul Park <byungchul.park@lge.com> wrote:
> [snip]
> > > - There is a bug in the CPU stopper machinery itself preventing it
> > > from scheduling the stopper on Y. Even though Y is not holding up the
> > > grace period.
> >
> > Or any thread on Y is busy with preemption/irq disabled preventing the
> > stopper from being scheduled on Y.
> >
> > Or something is stuck in ttwu() to wake up the stopper on Y due to any
> > scheduler locks such as pi_lock or rq->lock or something.
> >
> > I think what you mentioned can happen easily.
> >
> > Basically we would need information about preemption/irq disabled
> > sections on Y and scheduler's current activity on every cpu at that time.
>
> I think all that's needed is an NMI backtrace on all CPUs. An ARM we
> don't have NMI solutions and only IPI or interrupt based backtrace
> works which should at least catch and the preempt disable and softirq
> disable cases.
>
> But yeah I don't see why just the stacks of those CPUs that are
> blocking the CPU X would not suffice for the trivial cases where a
> piece of misbehaving code disable interrupts / preemption and
> prevented the stopper thread from executing.
Right. So it makes more interesting tho! :-)
> May be once the test case is ready (no rush!) , then it will be more
> clear what can help.
Yes. I'm really happy to help things about RCU that I love, fixed or
improved. And with the the test case or a real issue, I believe I can do
more helpful work. Looking forward to it, too (no rush!).
Thanks,
Byungchul
next prev parent reply other threads:[~2019-07-19 1:11 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-08 6:00 [PATCH] rcu: Make jiffies_till_sched_qs writable Byungchul Park
2019-07-08 12:50 ` Paul E. McKenney
2019-07-08 13:03 ` Joel Fernandes
2019-07-08 13:19 ` Paul E. McKenney
2019-07-08 14:15 ` Joel Fernandes
2019-07-09 6:05 ` Byungchul Park
2019-07-09 12:43 ` Paul E. McKenney
2019-07-09 5:58 ` Byungchul Park
2019-07-09 6:45 ` Byungchul Park
2019-07-09 12:41 ` Paul E. McKenney
2019-07-10 1:20 ` Byungchul Park
2019-07-11 12:30 ` Paul E. McKenney
2019-07-11 13:08 ` Joel Fernandes
2019-07-11 15:02 ` Paul E. McKenney
2019-07-11 16:48 ` Joel Fernandes
2019-07-11 19:58 ` Joel Fernandes
2019-07-12 6:32 ` Byungchul Park
2019-07-12 12:51 ` Joel Fernandes
2019-07-12 13:02 ` Paul E. McKenney
2019-07-12 13:43 ` Joel Fernandes
2019-07-12 14:53 ` Paul E. McKenney
2019-07-13 8:47 ` Byungchul Park
2019-07-13 14:20 ` Joel Fernandes
2019-07-13 15:13 ` Paul E. McKenney
2019-07-13 15:42 ` Joel Fernandes
2019-07-13 17:41 ` Paul E. McKenney
2019-07-14 13:39 ` Byungchul Park
2019-07-14 13:56 ` Paul E. McKenney
2019-07-15 17:39 ` Joel Fernandes
2019-07-15 20:09 ` Paul E. McKenney
2019-07-18 16:14 ` Joel Fernandes
2019-07-18 16:15 ` Joel Fernandes
2019-07-18 21:34 ` Paul E. McKenney
2019-07-19 0:48 ` Joel Fernandes
2019-07-19 0:54 ` Byungchul Park
2019-07-19 0:39 ` Byungchul Park
2019-07-19 0:52 ` Joel Fernandes
2019-07-19 1:10 ` Byungchul Park [this message]
2019-07-19 7:43 ` Paul E. McKenney
2019-07-19 9:57 ` Byungchul Park
2019-07-19 19:57 ` Paul E. McKenney
2019-07-19 20:33 ` Joel Fernandes
2019-07-23 11:05 ` Byungchul Park
2019-07-23 13:47 ` Paul E. McKenney
2019-07-23 16:54 ` Paul E. McKenney
2019-07-24 7:58 ` Byungchul Park
2019-07-24 7:59 ` Byungchul Park
2019-07-12 13:01 ` Paul E. McKenney
2019-07-12 13:40 ` Joel Fernandes
2019-07-12 6:00 ` Byungchul Park
2019-07-12 5:52 ` Byungchul Park
2019-07-12 5:48 ` Byungchul Park
2019-07-13 9:08 ` Byungchul Park
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