From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753168Ab1AFGAB (ORCPT ); Thu, 6 Jan 2011 01:00:01 -0500 Received: from e7.ny.us.ibm.com ([32.97.182.137]:37291 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1749667Ab1AFGAA (ORCPT ); Thu, 6 Jan 2011 01:00:00 -0500 Date: Wed, 5 Jan 2011 21:59:56 -0800 From: "Paul E. McKenney" To: Lai Jiangshan Cc: Arnd Bergmann , Ingo Molnar , LKML Subject: Re: [PATCH] rcu: remove SPARSE_RCU_POINTER Message-ID: <20110106055956.GB2506@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <4D22DD95.7050308@cn.fujitsu.com> <201101041136.02514.arnd@arndb.de> <20110104211938.GT2026@linux.vnet.ibm.com> <4D23C9B0.9060803@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4D23C9B0.9060803@cn.fujitsu.com> User-Agent: Mutt/1.5.20 (2009-06-14) X-Content-Scanned: Fidelis XPS MAILER Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 05, 2011 at 09:30:24AM +0800, Lai Jiangshan wrote: > On 01/05/2011 05:19 AM, Paul E. McKenney wrote: > > On Tue, Jan 04, 2011 at 11:36:02AM +0100, Arnd Bergmann wrote: > >> On Tuesday 04 January 2011 09:43:01 Lai Jiangshan wrote: > >>> As I known, __rcu annotations do not effect the result compiled kernel. > >>> > >>> They work only when we use spare("make C=1" or "make C=2"), > >>> So we don't need another new switch for it since we have one > >>> for debugging(use spare or not). > >>> > >>> signed-off-by: Lai Jiangshan > >> > >> The intention of this option was to avoid introducing an excessive > >> number of false positives when using sparse. > >> > >> We should only make that unconditional if we are reasonably convinced > >> that all the majority of warnings caused by it should actually > >> lead to changes in the code. > > > > I agree with Arnd here -- the changes required are extensive in many > > cases, and a number of subsystems are making decent progress. > > > > Thanx, Paul > > I also agree. Most guys like to use direct read to the rcu pointer > on update side or direct read/write when initializing the rcu pointer. > This causes a lot of false positives. And it is good to see some people, most notably Eric Dumazet, making good use of __rcu! We will learn from the experiences of the early adopters, and perhaps be more aggressive pushing __rcu out to the rest of the community in a year or two, depending on how it goes. It is quite possible that __rcu will be something that only some of the maintainers make use of for some time -- and that is OK. Thanx, Paul