On Wed, 11 Jul 2018 21:28:25 -0700 Joel Fernandes <[email protected]> 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 <[email protected]> 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. -- Steve
