From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932889Ab2IDXO1 (ORCPT ); Tue, 4 Sep 2012 19:14:27 -0400 Received: from e37.co.us.ibm.com ([32.97.110.158]:38187 "EHLO e37.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932839Ab2IDXO0 (ORCPT ); Tue, 4 Sep 2012 19:14:26 -0400 Date: Tue, 4 Sep 2012 16:14:15 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: Josh Triplett , 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: <20120904231415.GW2593@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1346799082.27919.31.camel@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12090423-7408-0000-0000-000008307A7D Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 :-( Very good -- I will add this to the commit log, with attribution. Thanx, Paul