On Thu, Aug 22, 2019 at 09:36:21PM -0500, Scott Wood wrote:
> On Wed, 2019-08-21 at 16:33 -0700, Paul E. McKenney wrote:
> > On Wed, Aug 21, 2019 at 06:19:04PM -0500, Scott Wood wrote:
> > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> > > index 388ace315f32..d6e357378732 100644
> > > --- a/include/linux/rcupdate.h
> > > +++ b/include/linux/rcupdate.h
> > > @@ -615,10 +615,12 @@ static inline void rcu_read_unlock(void)
> > > static inline void rcu_read_lock_bh(void)
> > > {
> > > local_bh_disable();
> > > +#ifndef CONFIG_PREEMPT_RT_FULL
> > > __acquire(RCU_BH);
> > > rcu_lock_acquire(&rcu_bh_lock_map);
> > > RCU_LOCKDEP_WARN(!rcu_is_watching(),
> > > "rcu_read_lock_bh() used illegally while idle");
> > > +#endif
> >
> > Any chance of this using "if (!IS_ENABLED(CONFIG_PREEMPT_RT_FULL))"?
> > We should be OK providing a do-nothing __maybe_unused rcu_bh_lock_map
> > for lockdep-enabled -rt kernels, right?
>
> OK.
>
> > > @@ -185,8 +189,10 @@ void __local_bh_enable_ip(unsigned long ip,
> > > > > unsigned int cnt)
> > > WARN_ON_ONCE(count < 0);
> > > local_irq_enable();
> > >
> > > - if (!in_atomic())
> > > + if (!in_atomic()) {
> > > + rcu_read_unlock();
> > > local_unlock(bh_lock);
> > > + }
> >
> > The return from in_atomic() is guaranteed to be the same at
> > local_bh_enable() time as was at the call to the corresponding
> > local_bh_disable()?
>
> That's an existing requirement on RT (which rcutorture currently violates)
> due to bh_lock.
>
> > I could have sworn that I ran afoul of this last year. Might these
> > added rcu_read_lock() and rcu_read_unlock() calls need to check for
> > CONFIG_PREEMPT_RT_FULL?
>
> This code is already under a PREEMPT_RT_FULL ifdef.
Good enough, then!
Thanx, Paul
