Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932341AbaFBVD4 (ORCPT ); Mon, 2 Jun 2014 17:03:56 -0400 Received: from e33.co.us.ibm.com ([32.97.110.151]:55244 "EHLO e33.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932179AbaFBVDz (ORCPT ); Mon, 2 Jun 2014 17:03:55 -0400 Date: Mon, 2 Jun 2014 14:03:48 -0700 From: "Paul E. McKenney" To: Linus Torvalds Cc: Peter Zijlstra , Mikulas Patocka , "James E.J. Bottomley" , Helge Deller , John David Anglin , Parisc List , Linux Kernel Mailing List , "Vinod, Chegu" , Waiman Long , 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: <20140602210348.GF22231@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20140602162525.GH16155@laptop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14060221-0928-0000-0000-0000025BA7DB Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 02, 2014 at 10:09:35AM -0700, Linus Torvalds wrote: > On Mon, Jun 2, 2014 at 9:25 AM, Peter Zijlstra wrote: > > > > And I can't say I'm a particular fan of these ops either, as alternative > > I'm almost inclined to just exclude parisc from using opt spinning. > > Please do. > > There is no way in hell that we should introduce a magic new > atomic_pointer thing for parisc. And the idea somebody had to change > ACCESS_ONCE() for PA-RISC (I'm not going to go back to find who to > blame) is just horribly wrong too, since it's not even necessary for > any normal use: the special "load-and-store-zero" instruction isn't > actually used for "real" data, it's used only for the special > spinlocks afaik, so doing it for all ACCESS_ONCE() users would be > wrong even on PA-RISC. For any normal data, the usual "just load the > value, making sure the compiler doesn't reload it" is perfectly fine - > even on PA-RISC. Guilty to charges as read on suggesting PA-RISC-specific ACCESS_ONCE(). ;-) Thanx, Paul > Now, if PA-RISC was a major architecture, we'd have to figure this > out. But as it is, PA-RISC is just about the shittiest RISC ever > invented (with original sparc being a strong contender), and let's > face it, nobody really uses it. It's a "fun project", but it is not > something that we should use to mess up either ACCESS_ONCE() or the > MCS locks. > > Just make PA-RISC use its own locks, not any of the new fancy ones. > > Linus > -- 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/