From mboxrd@z Thu Jan 1 00:00:00 1970 From: paulmck at linux.vnet.ibm.com (Paul E. McKenney) Date: Wed, 11 Jul 2018 08:15:59 -0700 Subject: [PATCH v9 4/7] tracepoint: Make rcuidle tracepoint callers use SRCU In-Reply-To: <20180711104618.05dc4b46@gandalf.local.home> References: <20180628182149.226164-1-joel@joelfernandes.org> <20180628182149.226164-5-joel@joelfernandes.org> <20180711124954.GE2476@hirez.programming.kicks-ass.net> <20180711090003.42596c2b@gandalf.local.home> <20180711142744.GN3593@linux.vnet.ibm.com> <20180711104618.05dc4b46@gandalf.local.home> Message-ID: <20180711151559.GR3593@linux.vnet.ibm.com> On Wed, Jul 11, 2018 at 10:46:18AM -0400, Steven Rostedt wrote: > On Wed, 11 Jul 2018 07:27:44 -0700 > "Paul E. McKenney" wrote: > > > On Wed, Jul 11, 2018 at 09:00:03AM -0400, Steven Rostedt wrote: > > > On Wed, 11 Jul 2018 14:49:54 +0200 > > > Peter Zijlstra wrote: > > > > > > > On Thu, Jun 28, 2018 at 11:21:46AM -0700, Joel Fernandes wrote: > > > > > - it_func_ptr = rcu_dereference_sched((tp)->funcs); \ > > > > > > > > I would convert to rcu_dereference_raw() to appease sparse. The fancy > > > > stuff below is pointless if you then turn off all checking. > > > > > > The problem with doing this is if we use a trace event without the > > > proper _idle() or whatever, we wont get a warning that it is used > > > incorrectly with lockdep. Or does lockdep still check if "rcu is > > > watching" with rcu_dereference_raw()? > > > > No lockdep checking is done by rcu_dereference_raw(). > > Correct, but I think we can do this regardless. So Joel please resend > with Peter's suggestion. > > The reason being is because of this: > > > #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. Indeed, the rcu_dereference_sched() would catch it in that case, so agreed, Peter's suggestion isn't losing any debuggability. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kselftest" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html From mboxrd@z Thu Jan 1 00:00:00 1970 From: paulmck@linux.vnet.ibm.com (Paul E. McKenney) Date: Wed, 11 Jul 2018 08:15:59 -0700 Subject: [PATCH v9 4/7] tracepoint: Make rcuidle tracepoint callers use SRCU In-Reply-To: <20180711104618.05dc4b46@gandalf.local.home> References: <20180628182149.226164-1-joel@joelfernandes.org> <20180628182149.226164-5-joel@joelfernandes.org> <20180711124954.GE2476@hirez.programming.kicks-ass.net> <20180711090003.42596c2b@gandalf.local.home> <20180711142744.GN3593@linux.vnet.ibm.com> <20180711104618.05dc4b46@gandalf.local.home> Message-ID: <20180711151559.GR3593@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" Message-ID: <20180711151559.BXRqt2xd1c1Clbxou4pk24L9oulFirgCdnVqIqPxRIk@z> On Wed, Jul 11, 2018@10:46:18AM -0400, Steven Rostedt wrote: > On Wed, 11 Jul 2018 07:27:44 -0700 > "Paul E. McKenney" wrote: > > > On Wed, Jul 11, 2018@09:00:03AM -0400, Steven Rostedt wrote: > > > On Wed, 11 Jul 2018 14:49:54 +0200 > > > Peter Zijlstra wrote: > > > > > > > On Thu, Jun 28, 2018 at 11:21:46AM -0700, Joel Fernandes wrote: > > > > > - it_func_ptr = rcu_dereference_sched((tp)->funcs); \ > > > > > > > > I would convert to rcu_dereference_raw() to appease sparse. The fancy > > > > stuff below is pointless if you then turn off all checking. > > > > > > The problem with doing this is if we use a trace event without the > > > proper _idle() or whatever, we wont get a warning that it is used > > > incorrectly with lockdep. Or does lockdep still check if "rcu is > > > watching" with rcu_dereference_raw()? > > > > No lockdep checking is done by rcu_dereference_raw(). > > Correct, but I think we can do this regardless. So Joel please resend > with Peter's suggestion. > > The reason being is because of this: > > > #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. Indeed, the rcu_dereference_sched() would catch it in that case, so agreed, Peter's suggestion isn't losing any debuggability. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kselftest" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html