From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932816Ab2IDWeD (ORCPT ); Tue, 4 Sep 2012 18:34:03 -0400 Received: from e7.ny.us.ibm.com ([32.97.182.137]:42204 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754251Ab2IDWeB (ORCPT ); Tue, 4 Sep 2012 18:34:01 -0400 Date: Tue, 4 Sep 2012 15:33:50 -0700 From: "Paul E. McKenney" To: Josh Triplett 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: <20120904223350.GQ2593@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120831180052.GB4259@jtriplet-mobl1> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12090422-5806-0000-0000-00001927FFF3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Thanx, Paul > - Josh Triplett > > > --- > > include/linux/rcupdate.h | 6 ++---- > > kernel/rcutiny.c | 2 ++ > > kernel/rcutree.c | 2 ++ > > 3 files changed, 6 insertions(+), 4 deletions(-) > > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > index 115ead2..0fbbd52 100644 > > --- a/include/linux/rcupdate.h > > +++ b/include/linux/rcupdate.h > > @@ -210,14 +210,12 @@ extern void exit_rcu(void); > > * to nest RCU_NONIDLE() wrappers, but the nesting level is currently > > * quite limited. If deeper nesting is required, it will be necessary > > * to adjust DYNTICK_TASK_NESTING_VALUE accordingly. > > - * > > - * This macro may be used from process-level code only. > > */ > > #define RCU_NONIDLE(a) \ > > do { \ > > - rcu_idle_exit(); \ > > + rcu_irq_enter(); \ > > do { a; } while (0); \ > > - rcu_idle_enter(); \ > > + rcu_irq_exit(); \ > > } while (0) > > > > /* > > diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c > > index e4163c5..2e073a2 100644 > > --- a/kernel/rcutiny.c > > +++ b/kernel/rcutiny.c > > @@ -115,6 +115,7 @@ void rcu_irq_exit(void) > > rcu_idle_enter_common(newval); > > local_irq_restore(flags); > > } > > +EXPORT_SYMBOL_GPL(rcu_irq_exit); > > > > /* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */ > > static void rcu_idle_exit_common(long long oldval) > > @@ -172,6 +173,7 @@ void rcu_irq_enter(void) > > rcu_idle_exit_common(oldval); > > local_irq_restore(flags); > > } > > +EXPORT_SYMBOL_GPL(rcu_irq_enter); > > > > #ifdef CONFIG_DEBUG_LOCK_ALLOC > > > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > > index f280e54..96b8aff 100644 > > --- a/kernel/rcutree.c > > +++ b/kernel/rcutree.c > > @@ -447,6 +447,7 @@ void rcu_irq_exit(void) > > rcu_idle_enter_common(rdtp, oldval); > > local_irq_restore(flags); > > } > > +EXPORT_SYMBOL_GPL(rcu_irq_exit); > > > > /* > > * rcu_idle_exit_common - inform RCU that current CPU is moving away from idle > > @@ -542,6 +543,7 @@ void rcu_irq_enter(void) > > rcu_idle_exit_common(rdtp, oldval); > > local_irq_restore(flags); > > } > > +EXPORT_SYMBOL_GPL(rcu_irq_enter); > > > > /** > > * rcu_nmi_enter - inform RCU of entry to NMI context > > -- > > 1.7.8 > > >