From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933077Ab2IFSyO (ORCPT ); Thu, 6 Sep 2012 14:54:14 -0400 Received: from relay4-d.mail.gandi.net ([217.70.183.196]:58792 "EHLO relay4-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932919Ab2IFSyM (ORCPT ); Thu, 6 Sep 2012 14:54:12 -0400 X-Originating-IP: 217.70.178.144 X-Originating-IP: 173.246.103.110 Date: Thu, 6 Sep 2012 11:54:02 -0700 From: Josh Triplett To: "Paul E. McKenney" Cc: Steven Rostedt , linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org, "Paul E. McKenney" Subject: Re: [PATCH tip/core/rcu 04/15] rcu: Permit RCU_NONIDLE() to be used from interrupt context Message-ID: <20120906185402.GB5738@jtriplet-mobl1> References: <20120830185607.GA32148@linux.vnet.ibm.com> <1346352988-32444-1-git-send-email-paulmck@linux.vnet.ibm.com> <1346352988-32444-4-git-send-email-paulmck@linux.vnet.ibm.com> <20120831180052.GB4259@jtriplet-mobl1> <20120904223350.GQ2593@linux.vnet.ibm.com> <1346799082.27919.31.camel@gandalf.local.home> <20120904230834.GB11494@jtriplet-mobl1> <1346801031.27919.39.camel@gandalf.local.home> <20120904233344.GB11855@jtriplet-mobl1> <20120904234307.GY2593@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120904234307.GY2593@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 04, 2012 at 04:43:07PM -0700, Paul E. McKenney wrote: > On Tue, Sep 04, 2012 at 04:33:44PM -0700, Josh Triplett wrote: > > On Tue, Sep 04, 2012 at 07:23:51PM -0400, Steven Rostedt wrote: > > > On Tue, 2012-09-04 at 16:08 -0700, Josh Triplett wrote: > > > > On Tue, Sep 04, 2012 at 06:51:22PM -0400, Steven Rostedt wrote: > > > > > On Tue, 2012-09-04 at 15:33 -0700, Paul E. McKenney wrote: > > > > > > On Fri, Aug 31, 2012 at 11:00:52AM -0700, Josh Triplett wrote: > > > > > > > On Thu, Aug 30, 2012 at 11:56:17AM -0700, Paul E. McKenney wrote: > > > > > > > > From: "Paul E. McKenney" > > > > > > > > > > > > > > > > There is a need to use RCU from interrupt context, but either before > > > > > > > > rcu_irq_enter() is called or after rcu_irq_exit() is called. If the > > > > > > > > interrupt occurs from idle, then lockdep-RCU will complain about such > > > > > > > > uses, as they appear to be illegal uses of RCU from the idle loop. > > > > > > > > In other environments, RCU_NONIDLE() could be used to properly protect > > > > > > > > the use of RCU, but RCU_NONIDLE() currently cannot be invoked except > > > > > > > > from process context. > > > > > > > > > > > > > > > > This commit therefore modifies RCU_NONIDLE() to permit its use more > > > > > > > > globally. > > > > > > > > > > > > > > > > Reported-by: Steven Rostedt > > > > > > > > Signed-off-by: Paul E. McKenney > > > > > > > > Signed-off-by: Paul E. McKenney > > > > > > > > > > > > > > Something seems wrong about this. The addition of EXPORT_SYMBOL_GPL > > > > > > > suggests that such interrupt handlers might live in modules. In what > > > > > > > situation might a module interrupt handler get called from the idle > > > > > > > loop, before rcu_irq_enter or after rcu_irq_exit, and need to know that > > > > > > > when using RCU? > > > > > > > > > > > > Drivers can be in modules, in which case their interrupt handlers will > > > > > > also be in the corresponding module. I do agree that in most cases, > > > > > > the irq_enter() and irq_exit() hooks would be invoked by non-module code, > > > > > > but I do believe that I had to add those exports due to build failures. > > > > > > > > > > > > Steven will let me know if I am confused on this point. > > > > > > > > > > > > > > > > You're not confused, the situation is confusing :-/ > > > > > > > > > > Because some trace events happen inside the idle loop after rcu has > > > > > "shutdown", we needed to create "trace_foo_rcuidle()" handlers that can > > > > > handle this condition. That is, for every trace_foo() static inline > > > > > (used at the tracepoint location), there exists a static inline > > > > > trace_foo_rcuidle(), that looks something like this: > > > > > > > > > > static inline void trace_##name##_rcuidle(proto) { > > > > > if (static_key_false(&__tracepoint_##name.key)) { > > > > > rcu_idle_exit(); > > > > > __DO_TRACE(); > > > > > rcu_idle_enter(); > > > > > } > > > > > } > > > > > > > > > > Although these calls are never used by module code, because they are > > > > > static inlines, they are still defined for all tracepoints, kernel > > > > > tracepoints as well as module tracepoints. And thus, need the export :-( > > > > > > > > Fair enough. > > > > > > > > What about having the tracepoint code generation detect when building as > > > > part of a module via defined(MODULE), and omit the unused _rcuidle > > > > versions in those cases? That would avoid the need to export those > > > > functions at all. Strawman patch (not tested): > > > > > > > > diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h > > > > index 802de56..41e1ef2 100644 > > > > --- a/include/linux/tracepoint.h > > > > +++ b/include/linux/tracepoint.h > > > > @@ -136,6 +136,22 @@ static inline void tracepoint_synchronize_unregister(void) > > > > postrcu; \ > > > > } while (0) > > > > > > > > +#ifdef 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), \ > > > > + rcu_idle_exit(), \ > > > > + rcu_idle_enter()); \ > > > > + } > > > > +#else > > > > +#define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args) > > > > +#endif > > > > + > > > > > > Egad! More macros on top of macros! Yeah I know I'm the most guilty of > > > this, but it just seems to add one more indirection that I would like to > > > avoid. > > > > This doesn't seem to add a significant amount of complexity; it forwards > > exactly the same parameters to the helper macro, and just moves the one > > function definition there and makes it conditional. This still seems > > more preferable than exporting functions just so they won't get called. > > > > > > /* > > > > * Make sure the alignment of the structure in the __tracepoints section will > > > > * not add unwanted padding between the beginning of the section and the > > > > @@ -151,16 +167,7 @@ static inline void tracepoint_synchronize_unregister(void) > > > > TP_ARGS(data_args), \ > > > > TP_CONDITION(cond),,); \ > > > > } \ > > > > - 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), \ > > > > - rcu_idle_exit(), \ > > > > - rcu_idle_enter()); \ > > > > - } \ > > > > + __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args) \ > > > > static inline int \ > > > > register_trace_##name(void (*probe)(data_proto), void *data) \ > > > > { \ > > > > > > > > > > > > If that doesn't work out, please consider adding an explicit comment > > > > saying why you exported the functions. > > > > > > > > > > Or, we could also add in include/linux/rcupdate.h: > > > > > > #ifdef MODULE > > > static inline void rcu_idle_enter(void) { > > > panic("Don't call me from modules"); > > > } > > > static inline void rcu_idle_exit(void) { > > > panic("Don't call me from modules"); > > > } > > > #else > > > extern void rcu_idle_enter(void); > > > extern void rcu_idle_exit(void); > > > #endif > > > > I could live with that; it seems preferable to unnecessary exports, > > though it still seems much uglier to me than the conditional definition > > of trace_*_rcuidle. :) > > Not sure I see much difference in aesthetics between the three approaches, > but am willing to switch over to a generally agreed-upon scheme. Steve, could I get an ack from you on the patch I sent? - Josh Triplett