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.
-- Steve
