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Message-ID: <20190627103455.01014276@gandalf.local.home>
Date: Thu, 27 Jun 2019 10:34:55 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Joel Fernandes <joel@...lfernandes.org>
Cc: "Paul E. McKenney" <paulmck@...ux.ibm.com>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Josh Triplett <josh@...htriplett.org>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [RFC] Deadlock via recursive wakeup via RCU with threadirqs
On Thu, 27 Jun 2019 10:24:36 -0400
Joel Fernandes <joel@...lfernandes.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
> rcu_read_unlock()
> -> rcu_read_unlock_special
> -> raise_softirq_irqoff
> -> wakeup_softirq <--- because in_interrupt returns false.
>
> I think the issue is in_interrupt() does not know about threaded interrupts.
> If it did, then the ksoftirqd wake up would not happen.
>
> Did I get something wrong?
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