From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932925Ab2IDXXz (ORCPT ); Tue, 4 Sep 2012 19:23:55 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:14502 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932852Ab2IDXXx (ORCPT ); Tue, 4 Sep 2012 19:23:53 -0400 X-Authority-Analysis: v=2.0 cv=C49rOHz+ c=1 sm=0 a=rXTBtCOcEpjy1lPqhTCpEQ==:17 a=mNMOxpOpBa8A:10 a=jUoZk2RAzk0A:10 a=5SG0PmZfjMsA:10 a=Q9fys5e9bTEA:10 a=meVymXHHAAAA:8 a=7zoRB9YQJIYA:10 a=imTROTZUkysA:10 a=RAM01ziftVcA:10 a=wFfiXLW5-aMA:10 a=56vLhSP8h14A:10 a=2eRPLDGB9N0A:10 a=KKAkSRfTAAAA:8 a=VnNF1IyMAAAA:8 a=Fi82Y59vGp6yMpx_A38A:9 a=PUjeQqilurYA:10 a=WwgC8nHKvroA:10 a=jeBq3FmKZ4MA:10 a=rXTBtCOcEpjy1lPqhTCpEQ==:117 X-Cloudmark-Score: 0 X-Originating-IP: 74.67.115.198 Message-ID: <1346801031.27919.39.camel@gandalf.local.home> Subject: Re: [PATCH tip/core/rcu 04/15] rcu: Permit RCU_NONIDLE() to be used from interrupt context From: Steven Rostedt To: Josh Triplett Cc: paulmck@linux.vnet.ibm.com, 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" Date: Tue, 04 Sep 2012 19:23:51 -0400 In-Reply-To: <20120904230834.GB11494@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> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.4.3-1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > /* > * 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 Hmm, if there ever happens to be a governor that can be loaded as a module, and if it has a tracepoint, then it would require this too. But the first time someone tries that, it will panic with the above code ;-) -- Steve