From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A2E1AC00319 for ; Thu, 21 Feb 2019 15:11:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7217A20823 for ; Thu, 21 Feb 2019 15:11:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="Tctc8enw" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728197AbfBUPLC (ORCPT ); Thu, 21 Feb 2019 10:11:02 -0500 Received: from mail-qt1-f193.google.com ([209.85.160.193]:44344 "EHLO mail-qt1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727696AbfBUPLB (ORCPT ); Thu, 21 Feb 2019 10:11:01 -0500 Received: by mail-qt1-f193.google.com with SMTP id d2so6157524qti.11 for ; Thu, 21 Feb 2019 07:11:00 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=OfiyWt0nyZYpi1WZA8fh11x04uRedVVor5lXLAWzvDU=; b=Tctc8enw4VBqqUguz44H8pGhWtxEhSCBRy5We/JpX53ACCek7VX4X87rZMixWQkixL D91S1dvDeYq1MZ/3FTCnUPMXJ/j5P32Bml5j0bTFXjKgWcIBAQGQtO7pj1fGe56gOWSm xxecRexVJ6AMCu86e5yHfifSYeNdi2dVAzY1Y= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=OfiyWt0nyZYpi1WZA8fh11x04uRedVVor5lXLAWzvDU=; b=ljhV3LkodG+A/dWoDXh375mM21LsFsXb40gJ27v/5qKGtvQljzuTWVQMRJs5Ro9Xzh ntjWim4EAm6A9To7S56J0k+vcRtLdAsCu0M8uvuA4u6eY/apQq83y+JsfARMZKV3OWM0 l8AoJhZEixrhZeuOwaWyKHHl5wJAk8VAbrt4bRBSMl7aFD2+3kh6zgKMEwxJgZaPGFVy pR/0bNlyo6SoNg1BUmtIn0nMs+NJ4BCPLoEMREcxw3MZeE/4TRTCbAMkv2OUk8IM5yT5 vk6lWyKzH2vzz1RGIBm4ZkT8pdH9uqy/QUeKQqbS1K1kChpXdce9frS/s/Vj8zvnScwO Aufg== X-Gm-Message-State: AHQUAuYjoY296ubFwRv8B6+ahA/ljoYdEPVuj0XeaW7HOQiZHfP7r7SI OimnXBbSYUMfsfK8xyBwYvk7eg== X-Google-Smtp-Source: AHgI3IZ75rH+4g9uggv+XkAvNL2+ZyCxpx+BttoJpwCekhf9VOxkt53FPt9Hyd9gMkLxha5HPuB/Mw== X-Received: by 2002:ac8:2b28:: with SMTP id 37mr10931322qtu.223.1550761860153; Thu, 21 Feb 2019 07:11:00 -0800 (PST) Received: from localhost ([2620:0:1004:1100:cca9:fccc:8667:9bdc]) by smtp.gmail.com with ESMTPSA id s128sm11596624qkh.59.2019.02.21.07.10.58 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 21 Feb 2019 07:10:58 -0800 (PST) Date: Thu, 21 Feb 2019 10:10:57 -0500 From: Joel Fernandes To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Alexei Starovoitov , Christian Brauner , Daniel Borkmann , David Ahern , "David S. Miller" , Ido Schimmel , Ingo Molnar , "moderated list:INTEL ETHERNET DRIVERS" , Jakub Kicinski , Jeff Kirsher , Jesper Dangaard Brouer , John Fastabend , Josh Triplett , keescook@chromium.org, Lai Jiangshan , Martin KaFai Lau , Mathieu Desnoyers , netdev@vger.kernel.org, "Paul E. McKenney" , rcu@vger.kernel.org, Song Liu , Steven Rostedt , xdp-newbies@vger.kernel.org, Yonghong Song Subject: Re: [PATCH RFC 4/5] sched/topology: Annonate RCU pointers properly Message-ID: <20190221151057.GA19213@google.com> References: <20190221054942.132388-1-joel@joelfernandes.org> <20190221054942.132388-5-joel@joelfernandes.org> <20190221091944.GY32477@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190221091944.GY32477@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Hi Peter, Thanks for taking a look. On Thu, Feb 21, 2019 at 10:19:44AM +0100, Peter Zijlstra wrote: > On Thu, Feb 21, 2019 at 12:49:41AM -0500, Joel Fernandes (Google) wrote: > > > Also replace rcu_assign_pointer call on rq->sd with WRITE_ONCE. This > > should be sufficient for the rq->sd initialization. > > > @@ -668,7 +668,7 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu) > > > > rq_attach_root(rq, rd); > > tmp = rq->sd; > > - rcu_assign_pointer(rq->sd, sd); > > + WRITE_ONCE(rq->sd, sd); > > dirty_sched_domain_sysctl(cpu); > > destroy_sched_domains(tmp); > > Where did the RELEASE barrier go? > > That was a publish operation, now it is not. Funny thing is, initially I had written this patch with smp_store_release() instead of WRITE_ONCE, but checkpatch complaints with that since it needs a comment on top of it, and I wasn't sure if RELEASE barrier was the intent of using rcu_assign_pointer (all the more reason to replace it with something more explicit). I will replace it with the following and resubmit it then: /* Release barrier */ smp_store_release(&rq->sd, sd); Or do we want to just drop the "Release barrier" comment and live with the checkpatch warning? (my same response applies to patch 5/5). thanks, - Joel