Re: [PATCH HACK RFC] cpu: Prevent late-arriving interrupts from disrupting offline

[Dietmar Eggemann]

On 6/3/19 1:44 PM, Mark Rutland wrote:
> On Mon, Jun 03, 2019 at 10:38:48AM +0200, Peter Zijlstra wrote:
> > On Sat, Jun 01, 2019 at 06:12:53PM -0700, Paul E. McKenney wrote:
> > > Scheduling-clock interrupts can arrive late in the CPU-offline process,
> > > after idle entry and the subsequent call to cpuhp_report_idle_dead().
> > > Once execution passes the call to rcu_report_dead(), RCU is ignoring
> > > the CPU, which results in lockdep complaints when the interrupt handler
> > > uses RCU:
> >
> > > diff --git a/kernel/cpu.c b/kernel/cpu.c
> > > index 448efc06bb2d..3b33d83b793d 100644
> > > --- a/kernel/cpu.c
> > > +++ b/kernel/cpu.c
> > > @@ -930,6 +930,7 @@ void cpuhp_report_idle_dead(void)
> > >   	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
> > >   
> > >   	BUG_ON(st->state != CPUHP_AP_OFFLINE);
> > > +	local_irq_disable();
> > >   	rcu_report_dead(smp_processor_id());
> > >   	st->state = CPUHP_AP_IDLE_DEAD;
> > >   	udelay(1000);
> >
> > Urgh... I'd almost suggest we do something like the below.
> >
> >
> > But then I started looking at the various arch_cpu_idle_dead()
> > implementations and ran into arm's implementation, which is calling
> > complete() where generic code already established this isn't possible
> > (see for example cpuhp_report_idle_dead()).
>
> IIRC, that should have been migrated over to cpu_report_death(), as
> arm64 was in commit:
>
>    05981277a4de1ad6 ("arm64: Use common outgoing-CPU-notification code")
>
> ... but it looks like Paul's patch to do so [1] fell through the cracks;
> I'm not aware of any reason that shouldn't have been taken.
>    
> [1] https://lore.kernel.org/lkml/1431467407-1223-8-git-send-email-paulmck@xxxxxxxxxxxxxxxxxx/
>
> Paul, do you want to resend that?

Please do. We're carrying this patch out-of-tree for while now in our 
EAS integration to get cpu hotplug tests passing on TC2 (arm).

-- Dietmar