From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757384Ab1EKQm3 (ORCPT ); Wed, 11 May 2011 12:42:29 -0400 Received: from e8.ny.us.ibm.com ([32.97.182.138]:57380 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754595Ab1EKQm0 (ORCPT ); Wed, 11 May 2011 12:42:26 -0400 Date: Wed, 11 May 2011 00:44:03 -0700 From: "Paul E. McKenney" To: Ingo Molnar 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: <20110511074403.GW2258@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <6921.1304989476@localhost> <20110510082029.GF2258@linux.vnet.ibm.com> <20110510085746.GG27426@elte.hu> <20110510162158.GK2258@linux.vnet.ibm.com> <20110510204443.GF21903@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110510204443.GF21903@elte.hu> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 10, 2011 at 10:44:43PM +0200, Ingo Molnar wrote: > > * 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)? Works for me -- and in this case it is quite easy to change existing uses. Thanx, Paul