On Wed, Jul 11, 2018 at 11:21:20PM -0400, Steven Rostedt wrote:
> On Wed, 11 Jul 2018 13:52:49 -0700
> Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> 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?
Meanwhile I'll drop that lockdep_recursion tomorrow and run some tests and
see how it behaves with Peter's changes.
thanks!
- Joel
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