On Wed, Mar 20, 2019 at 08:21:46AM -0700, Paul E. McKenney wrote:
> On Wed, Mar 20, 2019 at 12:32:19PM +0100, Sebastian Andrzej Siewior wrote:
> > On 2019-03-19 12:44:19 [+0100], To Paul E. McKenney wrote:
> > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > > index 0f31b79eb6761..0a719f726e149 100644
> > > --- a/kernel/rcu/tree.c
> > > +++ b/kernel/rcu/tree.c
> > …
> > > +/*
> > > + * Spawn per-CPU RCU core processing kthreads.
> > > + */
> > > +static int __init rcu_spawn_core_kthreads(void)
> > > +{
> > > + int cpu;
> > > +
> > > + for_each_possible_cpu(cpu)
> > > + per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0;
> > > + if (!IS_ENABLED(CONFIG_RCU_BOOST) && !rcu_softirq_enabled)
> >
> > and this needs to become
> > - if (!IS_ENABLED(CONFIG_RCU_BOOST) && !rcu_softirq_enabled)
> > + if (!IS_ENABLED(CONFIG_RCU_BOOST) && rcu_softirq_enabled)
> >
> > With this change and hunk that I just sent to Joel I get thee three RCU
> > modes with and without BOOST booted.
> >
> > Unless there is something (and Paul agrees that the Joel hunk is
> > correct) I would post a v3 with those changes included.
>
> Well, I did get a bunch of grace-period hangs of various sorts when I
> ran rcutorture like this:
>
> tools/testing/selftests/rcutorture/bin/kvm.sh --memory 1G --bootargs
> rcunosoftirq
>
> I also got a silent hard hang on TREE03. And an rcutorture forward-progress
> failure, which goes along with the grace-period hangs.
>
> So something does need adjustment. I will try again with this change.
And it does seem to work better. I will give it more intense testing
later on, but in the meantime I have merged this change into your
earlier patch.
We will see whether or not I am able summon up the courage to push it
into v5.2, however. ;-)
Thanx, Paul
> > > + return 0;
> > > + WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec), "%s:
> > > Could not start rcub kthread, OOM is now expected behavior\n", __func__);
> > > + return 0;
> > > +}
> > > +early_initcall(rcu_spawn_core_kthreads);
> >
> > Sebastian
> >
