Re: [PATCH RFC] tracepoint: Introduce tracepoint callbacks executing with preempt on

[Steven Rostedt]

On Fri, 27 Apr 2018 08:57:01 -0700
"Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> wrote:

> > +		if (preempt_on) {					\
> > +			WARN_ON_ONCE(in_nmi()); /* no srcu from nmi */	\  
> 
> Very good on this check, thank you!

I think you need to return and not call the read lock.

			if (WARN_ON_ONCE(in_nmi()))
				return;

> 
> > +			idx = srcu_read_lock(&tracepoint_srcu);         \  
> 
> Hmmm...  Do I need to create a _notrace variant of srcu_read_lock()
> and srcu_read_unlock()?

I think so.

-- Steve

> 
> > +			it_func_ptr = srcu_dereference((tp)->funcs,	\
> > +						&tracepoint_srcu);	\
> > +		} else {						\
> > +			rcu_read_lock_sched_notrace();			\
> > +			it_func_ptr =					\
> > +				rcu_dereference_sched((tp)->funcs);	\
> > +		}							\
> > +									\