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

Paul E. McKenney
2018-04-27T16:59:42Z

On Fri, Apr 27, 2018 at 12:46:41PM -0400, Steven Rostedt wrote:
> On Fri, 27 Apr 2018 09:45:54 -0700
> "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
>
> > > > That shouldn't be needed. For the rcu_read_lock_sched case, there is a
> > > > preempt_disable which needs to be a notrace, but for the srcu one,
> > > > since we don't do that, I think it should be fine.
> > >
> > > Actually, I think I may agree here too. Because the _notrace is for
> > > function tracing, and it shouldn't affect it. If people don't want it
> > > traced, they could add those functions to the list in the notrace file.
> >
> > OK, feel free to ignore my notrace srcu_read_lock() patch, then. ;-)
>
> Of course I wasn't thinking about the lockdep tracepoints that Joel
> mentioned, which happens to be the reason for all this discussion in
> the first place :-) Now I think we do need it. (OK, I can keep
> changing my mind, can't I?).

You can, but at some point I start applying heavy-duty hysteresis. ;-)

So the current thought (as of your having sent the above email) is that
we need notrace versions of srcu_read_lock() and srcu_read_unlock(),
but not for __srcu_read_lock() and __srcu_read_unlock(), correct?

Thanx, Paul