On Thu, Jul 12, 2018 at 09:35:12AM -0400, Steven Rostedt wrote:
> On Wed, 11 Jul 2018 21:28:25 -0700
> Joel Fernandes <j...@joelfernandes.org> wrote:
>
> > On Wed, Jul 11, 2018 at 11:21:20PM -0400, Steven Rostedt wrote:
> > > On Wed, 11 Jul 2018 13:52:49 -0700
> > > Joel Fernandes <j...@joelfernandes.org> wrote:
> > >
> > > > > #define __DECLARE_TRACE(name, proto, args, cond, data_proto,
> > > > > data_args) \
> > > > > extern struct tracepoint __tracepoint_##name;
> > > > > \
> > > > > static inline void trace_##name(proto)
> > > > > \
> > > > > {
> > > > > \
> > > > > if (static_key_false(&__tracepoint_##name.key))
> > > > > \
> > > > > __DO_TRACE(&__tracepoint_##name,
> > > > > \
> > > > > TP_PROTO(data_proto),
> > > > > \
> > > > > TP_ARGS(data_args),
> > > > > \
> > > > > TP_CONDITION(cond), 0);
> > > > > \
> > > > > if (IS_ENABLED(CONFIG_LOCKDEP) && (cond)) {
> > > > > \
> > > > > rcu_read_lock_sched_notrace();
> > > > > \
> > > > >
> > > > > rcu_dereference_sched(__tracepoint_##name.funcs);\
> > > > > rcu_read_unlock_sched_notrace();
> > > > > \
> > > > > }
> > > > > \
> > > > > }
> > > > >
> > > > > Because lockdep would only trigger warnings when the tracepoint was
> > > > > enabled and used in a place it shouldn't be, we added the above
> > > > > IS_ENABLED(CONFIG_LOCKDEP) part to test regardless if the the
> > > > > tracepoint was enabled or not. Because we do this, we don't need to
> > > > > have the test in the __DO_TRACE() code itself. That means we can clean
> > > > > up the code as per Peter's suggestion.
> > > >
> > > > Sounds good, I'm Ok with making this change.
> > > >
> > > > Just to clarify, are you proposing to change the rcu_dereference_sched
> > > > to
> > > > rcu_dereference_raw in both __DECLARE_TRACE and __DO_TRACE?
> > >
> > > No, just in __DO_TRACE(). The rcu_dereference_sched() above in
> > > __DECLARE_TRACE() in the if (IS_ENABLED(CONFIG_LOCKDEP) block is
> > > required to show the warnings if trace_##name() is used wrong, and is
> > > the reason we can use rcu_dereference_raw() in __DO_TRACE() in the
> > > first place ;-)
> > >
> > > This brings up another point. We should probably add to
> > > __DECLARE_TRACE_RCU() this:
> > >
> > > #ifndef MODULE
> > > #define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto,
> > > data_args) \
> > > static inline void trace_##name##_rcuidle(proto) \
> > > { \
> > > if (static_key_false(&__tracepoint_##name.key)) \
> > > __DO_TRACE(&__tracepoint_##name, \
> > > TP_PROTO(data_proto), \
> > > TP_ARGS(data_args), \
> > > TP_CONDITION(cond), 1); \
> > > + if (IS_ENABLED(CONFIG_LOCKDEP) && (cond)) { \
> > > + int idx; \
> > > + idx = srcu_read_lock_notrace(&tracepoint_srcu); \
> > > + srcu_dereference_notrace(__tracepoint_##name.funcs, \
> > > + &tracepoint_srcu); \
> > > + srcu_read_unlock_notrace(&tracepoint_srcu, idx); \
> > > + } \
> > > }
> > > #else
> > >
> > >
> > > So that lockdep works with trace_##name##__rcuidle() when the trace
> > > event is not enabled.
> > >
> > > But that should be a separate patch and not part of this series. I may
> > > write that up tomorrow.
> >
> > Yes, that sounds good to me and would be good to add the safe guard there.
> > But you meant srcu_dereference above, not srcu_dereference_notrace right?
>
> We don't need to trace them. I believe that the "srcu_*_notrace" still
> performs the lockdep checks. That's what we want. If they don't then we
> should not use notrace. But I believe they still do lockdep.
AFAICT, _notrace doesn't call into lockdep or tracing (there's also a comment
that says so):
/**
* srcu_dereference_notrace - no tracing and no lockdep calls from here
*/
So then, we should use the regular variant for this additional check you're
suggesting.
thanks,
- Joel
