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SubjectRe: [GIT PULL rcu/next] rcu commits for 2.6.40
On Mon, May 16, 2011 at 12:01:17AM +0200, Frederic Weisbecker wrote:
> On Sat, May 14, 2011 at 11:34:53AM -0700, Paul E. McKenney wrote:
> > rcutree.c | 91 +++++++++++++++++++++++++++++++++++++++++++++++++++-----------
> > 1 file changed, 75 insertions(+), 16 deletions(-)
> >
> > diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> > index a4a2ef0..0b541bd 100644
> > --- a/kernel/rcutree.c
> > +++ b/kernel/rcutree.c
> > @@ -308,23 +308,25 @@ static int rcu_implicit_offline_qs(struct rcu_data *rdp)
> >
> > #ifdef CONFIG_NO_HZ
> >
> > -/**
> > - * rcu_enter_nohz - inform RCU that current CPU is entering nohz
> > +/*
> > + * __rcu_enter_nohz - inform RCU that current CPU is entering nohz
> > *
> > * Enter nohz mode, in other words, -leave- the mode in which RCU
> > * read-side critical sections can occur. (Though RCU read-side
> > * critical sections can occur in irq handlers in nohz mode, a possibility
> > * handled by rcu_irq_enter() and rcu_irq_exit()).
> > + *
> > + * This variant should only be called from rcu_irq_exit() because it
> > + * assumes perfect nesting. The caller must have irqs disabled.
> > */
> > -void rcu_enter_nohz(void)
> > +void __rcu_enter_nohz(void)
> > {
> > - unsigned long flags;
> > struct rcu_dynticks *rdtp;
> >
> > - local_irq_save(flags);
> > rdtp = &__get_cpu_var(rcu_dynticks);
> > + WARN_ON_ONCE(rdtp->dynticks_nesting <= 0);
>
> But this warning will always trigger if it's called from rcu_irq_enter()
> after rcu_enter_nohz(). Right?

Hello, Frederic,

Thank you for looking this over!

But you lost me on this one. Isn't __rcu_enter_nohz() called from
rcu_irq_exit() rather than from rcu_irq_enter()?

Thanx, Paul


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