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

Scott Wood
2019-06-27T20:17:40Z

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