From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932858Ab2IDWst (ORCPT ); Tue, 4 Sep 2012 18:48:49 -0400 Received: from relay4-d.mail.gandi.net ([217.70.183.196]:52691 "EHLO relay4-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757824Ab2IDWss (ORCPT ); Tue, 4 Sep 2012 18:48:48 -0400 X-Originating-IP: 217.70.178.148 X-Originating-IP: 173.246.103.110 Date: Tue, 4 Sep 2012 15:48:39 -0700 From: Josh Triplett To: "Paul E. McKenney" Cc: 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, rostedt@goodmis.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: <20120904224839.GA11413@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120904223350.GQ2593@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 03:33:50PM -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. I definitely understand that drivers can have interrupt handlers in modules; however, I have a hard time seeing a case where a module has a legitimate reason to invoke rcu_irq_enter or rcu_irq_exit, or to run before the former or after the latter. - Josh Triplett