linux-kernel - Re: [RFC] Deadlock via recursive wakeup via RCU with threadirqs

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Date:   Thu, 27 Jun 2019 15:17:27 -0500
From:   Scott Wood <swood@...hat.com>
To:     paulmck@...ux.ibm.com, Joel Fernandes <joel@...lfernandes.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        rcu <rcu@...r.kernel.org>, LKML <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, 2019-06-27 at 11:41 -0700, Paul E. McKenney wrote:
> On Thu, Jun 27, 2019 at 02:16:38PM -0400, Joel Fernandes wrote:
> > 
> > I think the fix should be to prevent the wake-up not based on whether we
> > are
> > in hard/soft-interrupt mode but that we are doing the rcu_read_unlock()
> > from
> > a scheduler path (if we can detect that)
> 
> Or just don't do the wakeup at all, if it comes to that.  I don't know
> of any way to determine whether rcu_read_unlock() is being called from
> the scheduler, but it has been some time since I asked Peter Zijlstra
> about that.
> 
> Of course, unconditionally refusing to do the wakeup might not be happy
> thing for NO_HZ_FULL kernels that don't implement IRQ work.

Couldn't smp_send_reschedule() be used instead?

-Scott