Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753171AbaFBXRj (ORCPT ); Mon, 2 Jun 2014 19:17:39 -0400 Received: from e37.co.us.ibm.com ([32.97.110.158]:60136 "EHLO e37.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751800AbaFBXRh (ORCPT ); Mon, 2 Jun 2014 19:17:37 -0400 Date: Mon, 2 Jun 2014 16:17:30 -0700 From: "Paul E. McKenney" To: Eric Dumazet Cc: Linus Torvalds , Peter Zijlstra , Waiman Long , Mikulas Patocka , "James E.J. Bottomley" , Helge Deller , John David Anglin , Parisc List , Linux Kernel Mailing List , "Vinod, Chegu" , Thomas Gleixner , Rik van Riel , Andrew Morton , Davidlohr Bueso , Peter Anvin , Andi Kleen , "Chandramouleeswaran, Aswin" , "Norton, Scott J" , Jason Low Subject: Re: [PATCH v2] introduce atomic_pointer to fix a race condition in cancelable mcs spinlocks Message-ID: <20140602231730.GH22231@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20140602162525.GH16155@laptop.programming.kicks-ass.net> <20140602163032.GI16155@laptop.programming.kicks-ass.net> <538CB56E.5010709@hp.com> <20140602200525.GD13930@laptop.programming.kicks-ass.net> <20140602210227.GE22231@linux.vnet.ibm.com> <20140602220831.GG22231@linux.vnet.ibm.com> <1401749088.3645.189.camel@edumazet-glaptop2.roam.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1401749088.3645.189.camel@edumazet-glaptop2.roam.corp.google.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14060223-7164-0000-0000-0000022CAADB Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 02, 2014 at 03:44:48PM -0700, Eric Dumazet wrote: > On Mon, 2014-06-02 at 15:08 -0700, Paul E. McKenney wrote: > > > diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c > > index c639556f3fa0..c0120279dead 100644 > > --- a/kernel/rcu/srcu.c > > +++ b/kernel/rcu/srcu.c > > @@ -295,12 +295,15 @@ EXPORT_SYMBOL_GPL(cleanup_srcu_struct); > > int __srcu_read_lock(struct srcu_struct *sp) > > { > > int idx; > > + unsigned long *lp; > > > > idx = ACCESS_ONCE(sp->completed) & 0x1; > > preempt_disable(); > > - ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->c[idx]) += 1; > > + lp = this_cpu_ptr(&sp->per_cpu_ref->c[idx]); > > + ACCESS_ONCE(*lp) = *lp + 1; > > smp_mb(); /* B */ /* Avoid leaking the critical section. */ > > - ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->seq[idx]) += 1; > > + lp = this_cpu_ptr(&sp->per_cpu_ref->seq[idx]); > > + ACCESS_ONCE(*lp) = *lp + 1; > > preempt_enable(); > > return idx; > > > > This probably could use the following > > diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c > index c639556f3fa0..3a97eb6f9076 100644 > --- a/kernel/rcu/srcu.c > +++ b/kernel/rcu/srcu.c > @@ -298,9 +298,9 @@ int __srcu_read_lock(struct srcu_struct *sp) > > idx = ACCESS_ONCE(sp->completed) & 0x1; > preempt_disable(); > - ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->c[idx]) += 1; > + this_cpu_inc(sp->per_cpu_ref->c[idx]); > smp_mb(); /* B */ /* Avoid leaking the critical section. */ > - ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->seq[idx]) += 1; > + this_cpu_inc(sp->per_cpu_ref->seq[idx]); > preempt_enable(); > return idx; > } Good point! But given that I already have preemption disabled and given that __srcu_read_lock() is not to be used by irq handlers, I should be able to use __this_cpu_inc(), correct? Just to avoid unnecessary irq disabling on non-x86 platforms... Seems to pass a quick build, so trying a bit heavier testing. Thanx, Paul -- 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/