Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756895Ab3IEVhJ (ORCPT ); Thu, 5 Sep 2013 17:37:09 -0400 Received: from e33.co.us.ibm.com ([32.97.110.151]:59727 "EHLO e33.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753376Ab3IEVhG (ORCPT ); Thu, 5 Sep 2013 17:37:06 -0400 Date: Thu, 5 Sep 2013 13:59:59 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu Subject: Re: [PATCH] rcu: Is it safe to enter an RCU read-side critical section? Message-ID: <20130905205959.GN3966@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20130905195234.GA20555@linux.vnet.ibm.com> <20130905162558.6f13add0@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130905162558.6f13add0@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13090521-0928-0000-0000-0000014E89B9 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3217 Lines: 83 On Thu, Sep 05, 2013 at 04:25:58PM -0400, Steven Rostedt wrote: > On Thu, 5 Sep 2013 12:52:34 -0700 > "Paul E. McKenney" wrote: > > > There is currently no way for kernel code to determine whether it > > is safe to enter an RCU read-side critical section, in other words, > > whether or not RCU is paying attention to the currently running CPU. > > Given the large and increasing quantity of code shared by the idle loop > > and non-idle code, the this shortcoming is becoming increasingly painful. > > > > This commit therefore adds rcu_watching_this_cpu(), which returns true > > if it is safe to enter an RCU read-side critical section on the currently > > running CPU. This function is quite fast, using only a __this_cpu_read(). > > However, the caller must disable preemption. > > > > Reported-by: Steven Rostedt > > Signed-off-by: Paul E. McKenney > > Thanks Paul! > > > > > include/linux/rcupdate.h | 1 + > > kernel/rcutree.c | 12 ++++++++++++ > > 2 files changed, 13 insertions(+) > > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > index 15d33d9..1c7112c 100644 > > --- a/include/linux/rcupdate.h > > +++ b/include/linux/rcupdate.h > > @@ -225,6 +225,7 @@ extern void rcu_idle_enter(void); > > extern void rcu_idle_exit(void); > > extern void rcu_irq_enter(void); > > extern void rcu_irq_exit(void); > > +extern bool rcu_watching_this_cpu(void); > > > > #ifdef CONFIG_RCU_USER_QS > > extern void rcu_user_enter(void); > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > > index a06d172..7b8fcee 100644 > > --- a/kernel/rcutree.c > > +++ b/kernel/rcutree.c > > Don't we also need a rcutiny version too? Otherwise I'm guessing that > it wont compile if I use it with rcutiny (even if it always returns > true). Yep, there needs to be an rcutiny version, and it must work in the same way. So what I currently have is that the rcutiny version is under CONFIG_RCU_TRACE. This will require some Kconfig monkeying somewhere to select CONFIG_RCU_TRACE if CONFIG_SMP and tracing is enabled. Just trying to keep rcutiny tiny... Thanx, Paul > -- Steve > > > @@ -710,6 +710,18 @@ EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online); > > #endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */ > > > > /** > > + * rcu_watching_this_cpu - are RCU read-side critical sections safe? > > + * > > + * Return true if RCU is watching the running CPU, which means that this > > + * CPU can safely enter RCU read-side critical sections. The caller must > > + * have at least disabled preemption. > > + */ > > +bool rcu_watching_this_cpu(void) > > +{ > > + return !!__this_cpu_read(rcu_dynticks.dynticks_nesting); > > +} > > + > > +/** > > * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle > > * > > * If the current CPU is idle or running at a first-level (not nested) > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/