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Date: Wed, 11 Jul 2018 21:28:25 -0700 From: Joel Fernandes <joel@...lfernandes.org> To: Steven Rostedt <rostedt@...dmis.org> Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org, Boqun Feng <boqun.feng@...il.com>, Byungchul Park <byungchul.park@....com>, Ingo Molnar <mingo@...hat.com>, Julia Cartwright <julia@...com>, linux-kselftest@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Namhyung Kim <namhyung@...nel.org>, Thomas Glexiner <tglx@...utronix.de>, Tom Zanussi <tom.zanussi@...ux.intel.com> Subject: Re: [PATCH v9 4/7] tracepoint: Make rcuidle tracepoint callers use SRCU 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@...lfernandes.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? 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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