Re: [PATCH] rcu: Allow rcu_irq_enter_check_tick() from NMI

[Paul E. McKenney]

On Mon, Nov 16, 2020 at 06:24:31PM +0100, Thomas Gleixner wrote:
> On Mon, Nov 16 2020 at 13:10, Peter Zijlstra wrote:
> 
> > Any which way around; here's a proper patch...
> >
> > ---
> >
> > Subject: rcu: Allow rcu_irq_enter_check_tick() from NMI
> > From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Date: Mon Nov 16 12:54:56 CET 2020
> >
> > Eugenio managed to tickle #PF from NMI context which resulted in
> > hitting a WARN in RCU through irqentry_enter() ->
> > __rcu_irq_enter_check_tick().
> >
> > However, this situation is perfectly sane and does not warrant an
> > WARN. The #PF will (necessarily) be atomic and not require messing
> > with the tick state, so early return is correct.
> >
> > Fixes: aaf2bc50df1f ("rcu: Abstract out rcu_irq_enter_check_tick() from rcu_nmi_enter()")
> > Reported-by: "Eugenio Pérez" <eupm90@xxxxxxxxx>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> > Reviewed-by: Andy Lutomirski <luto@xxxxxxxxxx>
> > Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> 
> Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

Queued, thank you all!

							Thanx, Paul