From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752830Ab1EJUq0 (ORCPT ); Tue, 10 May 2011 16:46:26 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:38504 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752316Ab1EJUpA (ORCPT ); Tue, 10 May 2011 16:45:00 -0400 Date: Tue, 10 May 2011 22:44:43 +0200 From: Ingo Molnar To: "Paul E. McKenney" Cc: Valdis.Kletnieks@vt.edu, Andrew Morton , Peter Zijlstra , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: 2.6.39-rc6-mmotm0506 - lockdep splat in RCU code on page fault Message-ID: <20110510204443.GF21903@elte.hu> References: <6921.1304989476@localhost> <20110510082029.GF2258@linux.vnet.ibm.com> <20110510085746.GG27426@elte.hu> <20110510162158.GK2258@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110510162158.GK2258@linux.vnet.ibm.com> User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.3.1 -2.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Paul E. McKenney wrote: > On Tue, May 10, 2011 at 10:57:46AM +0200, Ingo Molnar wrote: > > > > * Paul E. McKenney wrote: > > > > > - raw_spin_lock_irqsave(&rnp->lock, flags); > > > - rnp->wakemask |= rdp->grpmask; > > > - raw_spin_unlock_irqrestore(&rnp->lock, flags); > > > + do { > > > + old = rnp->wakemask; > > > + new = old | rdp->grpmask; > > > + } while (cmpxchg(&rnp->wakemask, old, new) != old); > > > > Hm, isnt this an inferior version of atomic_or_long() in essence? > > > > Note that atomic_or_long() is x86 only, so a generic one would have to be > > offered too i suspect, atomic_cmpxchg() driven or so - which would look like > > the above loop. > > > > Most architectures could offer atomic_or_long() i suspect. > > Is the following what you had in mind? This (untested) patch provides only > the generic function: if this is what you had in mind, I can put together > optimized versions for a couple of the architectures. Yeah, something like this, except: > +#ifndef CONFIG_ARCH_HAS_ATOMIC_OR_LONG > +static inline void atomic_or_long(unsigned long *v1, unsigned long v2) > +{ > + unsigned long old; > + unsigned long new; > + > + do { > + old = ACCESS_ONCE(*v1); > + new = old | v2; > + } while (cmpxchg(v1, old, new) != old); > +} > +#endif /* #ifndef CONFIG_ARCH_HAS_ATOMIC_OR_LONG */ Shouldnt that method work on atomic_t (or atomic64_t)? Thanks, Ingo