From: Joel Fernandes <joel@joelfernandes.org>
To: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Steven Rostedt <rostedt@goodmis.org>, rcu <rcu@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Josh Triplett <josh@joshtriplett.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>
Subject: Re: [RFC] Deadlock via recursive wakeup via RCU with threadirqs
Date: Thu, 27 Jun 2019 14:27:22 -0400 [thread overview]
Message-ID: <20190627182722.GA216610@google.com> (raw)
In-Reply-To: <20190627181112.GY26519@linux.ibm.com>
On Thu, Jun 27, 2019 at 11:11:12AM -0700, Paul E. McKenney wrote:
> On Thu, Jun 27, 2019 at 01:46:27PM -0400, Joel Fernandes wrote:
> > On Thu, Jun 27, 2019 at 1:43 PM Joel Fernandes <joel@joelfernandes.org> wrote:
> > >
> > > On Thu, Jun 27, 2019 at 11:40 AM Sebastian Andrzej Siewior
> > > <bigeasy@linutronix.de> wrote:
> > > >
> > > > On 2019-06-27 11:37:10 [-0400], Joel Fernandes wrote:
> > > > > Sebastian it would be nice if possible to trace where the
> > > > > t->rcu_read_unlock_special is set for this scenario of calling
> > > > > rcu_read_unlock_special, to give a clear idea about whether it was
> > > > > really because of an IPI. I guess we could also add additional RCU
> > > > > debug fields to task_struct (just for debugging) to see where there
> > > > > unlock_special is set.
> > > > >
> > > > > Is there a test to reproduce this, or do I just boot an intel x86_64
> > > > > machine with "threadirqs" and run into it?
> > > >
> > > > Do you want to send me a patch or should I send you my kvm image which
> > > > triggers the bug on boot?
> > >
> > > I could reproduce this as well just booting Linus tree with threadirqs
> > > command line and running rcutorture. In 15 seconds or so it locks
> > > up... gdb backtrace shows the recursive lock:
> >
> > Sorry that got badly wrapped, so I pasted it here:
> > https://hastebin.com/ajivofomik.shell
>
> Which rcutorture scenario would that be? TREE03 is thus far refusing
> to fail for me when run this way:
>
> $ tools/testing/selftests/rcutorture/bin/kvm.sh --cpus 8 --duration 5 --trust-make --configs "TREE03" --bootargs "threadirqs"
I built x86_64_defconfig with CONFIG_PREEMPT enabled, then I ran it with
following boot params:
rcutorture.shutdown_secs=60 rcutorture.n_barrier_cbs=4 rcutree.kthread_prio=2
and also "threadirqs"
This was not a TREE config, but just my simple RCU test using qemu.
I will try this diff and let you know.
> If it had failed, I would have tried the patch shown below. I know that
> Sebastian has some concerns about the bug happening anyway, but we have
> to start somewhere! ;-)
>
> ------------------------------------------------------------------------
>
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 82c925df1d92..be7bafc2c0a0 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -624,25 +624,16 @@ static void rcu_read_unlock_special(struct task_struct *t)
> (rdp->grpmask & rnp->expmask) ||
> tick_nohz_full_cpu(rdp->cpu);
> // Need to defer quiescent state until everything is enabled.
> - if ((exp || in_irq()) && irqs_were_disabled && use_softirq &&
> - (in_irq() || !t->rcu_read_unlock_special.b.deferred_qs)) {
> - // Using softirq, safe to awaken, and we get
> - // no help from enabling irqs, unlike bh/preempt.
> - raise_softirq_irqoff(RCU_SOFTIRQ);
> - } else {
> - // Enabling BH or preempt does reschedule, so...
> - // Also if no expediting or NO_HZ_FULL, slow is OK.
> - set_tsk_need_resched(current);
> - set_preempt_need_resched();
> - if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled &&
> - !rdp->defer_qs_iw_pending && exp) {
> - // Get scheduler to re-evaluate and call hooks.
> - // If !IRQ_WORK, FQS scan will eventually IPI.
> - init_irq_work(&rdp->defer_qs_iw,
> - rcu_preempt_deferred_qs_handler);
> - rdp->defer_qs_iw_pending = true;
> - irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);
> - }
> + set_tsk_need_resched(current);
> + set_preempt_need_resched();
> + if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled &&
> + !rdp->defer_qs_iw_pending && exp) {
> + // Get scheduler to re-evaluate and call hooks.
> + // If !IRQ_WORK, FQS scan will eventually IPI.
> + init_irq_work(&rdp->defer_qs_iw,
> + rcu_preempt_deferred_qs_handler);
> + rdp->defer_qs_iw_pending = true;
> + irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);
Nice to see the code here got simplified ;-)
next prev parent reply other threads:[~2019-06-27 18:27 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-26 13:54 [RFC] Deadlock via recursive wakeup via RCU with threadirqs Sebastian Andrzej Siewior
2019-06-26 16:25 ` Paul E. McKenney
2019-06-27 7:47 ` Sebastian Andrzej Siewior
2019-06-27 15:52 ` Paul E. McKenney
2019-06-27 14:24 ` Joel Fernandes
2019-06-27 14:34 ` Steven Rostedt
2019-06-27 15:30 ` Joel Fernandes
2019-06-27 15:37 ` Joel Fernandes
2019-06-27 15:40 ` Sebastian Andrzej Siewior
2019-06-27 15:42 ` Joel Fernandes
2019-06-27 17:43 ` Joel Fernandes
2019-06-27 17:46 ` Joel Fernandes
2019-06-27 18:11 ` Paul E. McKenney
2019-06-27 18:27 ` Joel Fernandes [this message]
2019-06-27 18:51 ` Joel Fernandes
2019-06-27 19:14 ` Paul E. McKenney
2019-06-27 19:15 ` Paul E. McKenney
2019-06-27 18:30 ` Paul E. McKenney
2019-06-27 20:45 ` Paul E. McKenney
2019-06-27 15:55 ` Paul E. McKenney
2019-06-27 16:47 ` Joel Fernandes
2019-06-27 17:38 ` Paul E. McKenney
2019-06-27 18:16 ` Joel Fernandes
2019-06-27 18:41 ` Paul E. McKenney
2019-06-27 20:17 ` Scott Wood
2019-06-27 20:36 ` Paul E. McKenney
2019-06-28 7:31 ` Byungchul Park
2019-06-28 7:43 ` Byungchul Park
2019-06-28 8:14 ` Byungchul Park
2019-06-28 8:24 ` Byungchul Park
2019-06-28 12:24 ` Paul E. McKenney
2019-06-28 9:10 ` Byungchul Park
2019-06-28 9:28 ` Byungchul Park
2019-06-28 12:21 ` Paul E. McKenney
2019-06-28 10:40 ` Byungchul Park
2019-06-28 12:27 ` Paul E. McKenney
2019-06-28 15:44 ` Steven Rostedt
2019-06-29 15:12 ` Andrea Parri
2019-06-29 16:55 ` Paul E. McKenney
2019-06-29 18:09 ` Andrea Parri
2019-06-29 18:21 ` Andrea Parri
2019-06-29 19:15 ` Paul E. McKenney
2019-06-29 19:35 ` Andrea Parri
2019-06-30 23:55 ` Byungchul Park
2019-06-28 14:15 ` Peter Zijlstra
2019-06-28 15:54 ` Paul E. McKenney
2019-06-28 16:04 ` Peter Zijlstra
2019-06-28 17:20 ` Paul E. McKenney
2019-07-01 9:42 ` Peter Zijlstra
2019-07-01 10:24 ` Sebastian Andrzej Siewior
2019-07-01 12:23 ` Paul E. McKenney
2019-07-01 14:00 ` Peter Zijlstra
2019-07-01 16:01 ` Paul E. McKenney
2019-06-28 20:01 ` Scott Wood
2019-07-01 9:45 ` Peter Zijlstra
2019-06-28 13:54 ` Peter Zijlstra
2019-06-28 15:30 ` Paul E. McKenney
2019-06-28 18:40 ` Sebastian Andrzej Siewior
2019-06-28 18:52 ` Paul E. McKenney
2019-06-28 19:24 ` Joel Fernandes
2019-06-28 20:04 ` Paul E. McKenney
2019-06-28 21:40 ` Joel Fernandes
2019-06-28 22:25 ` Paul E. McKenney
2019-06-28 23:12 ` Joel Fernandes
2019-06-29 0:06 ` Paul E. McKenney
2019-06-28 16:40 ` Joel Fernandes
2019-06-28 16:45 ` Joel Fernandes
2019-06-28 17:30 ` Paul E. McKenney
2019-06-28 17:41 ` Paul E. McKenney
2019-06-28 17:45 ` Sebastian Andrzej Siewior
2019-06-28 18:07 ` Joel Fernandes
2019-06-28 18:20 ` Sebastian Andrzej Siewior
2019-07-01 2:08 ` Joel Fernandes
2019-06-28 18:22 ` Paul E. McKenney
2019-06-28 19:29 ` Joel Fernandes
2019-06-28 20:06 ` Paul E. McKenney
2019-06-28 18:05 ` Joel Fernandes
2019-06-28 18:23 ` Paul E. McKenney
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