From mboxrd@z Thu Jan 1 00:00:00 1970 From: joel@joelfernandes.org (Joel Fernandes) Date: Wed, 11 Jul 2018 13:56:39 -0700 Subject: [PATCH v9 4/7] tracepoint: Make rcuidle tracepoint callers use SRCU In-Reply-To: <20180711151559.GR3593@linux.vnet.ibm.com> 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> <20180711151559.GR3593@linux.vnet.ibm.com> Message-ID: <20180711205639.GB32091@joelaf.mtv.corp.google.com> Content-Type: text/plain; charset="UTF-8" Message-ID: <20180711205639.BYOSYfMBM3DM6qmeUWSPP2xj_vzgF3BWg5SMxQhsXIQ@z> On Wed, Jul 11, 2018@08:15:59AM -0700, Paul E. McKenney wrote: > 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. Hmm, but if we are doing the check later anyway, then why not do it in __DO_TRACE itself? Also I guess we are discussing about changing the rcu_dereference_sched which I think should go into a separate patch since my patch isn't touching how the rcuidle==0 paths use the RCU API. So I think this is an existing issue independent of this series. thanks! - Joel -- 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