From: Joel Fernandes <joel@joelfernandes.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <paulmck@linux.ibm.com>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
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 11:37:10 -0400 [thread overview]
Message-ID: <CAEXW_YT5LgdP_9SrachU4ZrhV9a7o_DM8eBfgxj=n7yRRyS-TQ@mail.gmail.com> (raw)
In-Reply-To: <20190627153031.GA249127@google.com>
On Thu, Jun 27, 2019 at 11:30 AM Joel Fernandes <joel@joelfernandes.org> wrote:
>
> On Thu, Jun 27, 2019 at 10:34:55AM -0400, Steven Rostedt wrote:
> > On Thu, 27 Jun 2019 10:24:36 -0400
> > Joel Fernandes <joel@joelfernandes.org> wrote:
> >
> > > > What am I missing here?
> > >
> > > This issue I think is
> > >
> > > (in normal process context)
> > > spin_lock_irqsave(rq_lock); // which disables both preemption and interrupt
> > > // but this was done in normal process context,
> > > // not from IRQ handler
> > > rcu_read_lock();
> > > <---------- IPI comes in and sets exp_hint
> >
> > How would an IPI come in here with interrupts disabled?
> >
> > -- Steve
>
> This is true, could it be rcu_read_unlock_special() got called for some
> *other* reason other than the IPI then?
>
> Per Sebastian's stack trace of the recursive lock scenario, it is happening
> during cpu_acct_charge() which is called with the rq_lock held.
>
> The only other reasons I know off to call rcu_read_unlock_special() are if
> 1. the tick indicated that the CPU has to report a QS
> 2. an IPI in the middle of the reader section for expedited GPs
> 3. preemption in the middle of a preemptible RCU reader section
>
> 1. and 2. are not possible because interrupts are disabled, that's why the
> wakeup_softirq even happened.
> 3. is not possible because we are holding rq_lock in the RCU reader section.
>
> So I am at a bit of a loss how this can happen :-(
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?
next prev parent reply other threads:[~2019-06-27 15:37 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 [this message]
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
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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