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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,T_DKIMWL_WL_HIGH 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 ABF14C282DC for ; Sun, 2 Jun 2019 21:02:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7FBD52412E for ; Sun, 2 Jun 2019 21:02:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1559509348; bh=QRRvQ5Cdm8o+ysb3bFXNhac8aAWSvjgYaFEeZiTAgCg=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=2vxQVlLfjknDB8FVC7xn6Yy5Hm5uJx61flZglJIeS1noOjyTm2Wq+TOOdE4/A9/Zh jC9+OFeHKh5kJf4oi7fki0E2Jd90O8rvae74xaeX+T/0d7pBfdxpiWBnk2XyIlHA5i yVLW7WdQq7kEKeJuIFqpW0O84TwMB91uViRNNG6M= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726980AbfFBVC1 (ORCPT ); Sun, 2 Jun 2019 17:02:27 -0400 Received: from mail-io1-f46.google.com ([209.85.166.46]:40572 "EHLO mail-io1-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726305AbfFBVC1 (ORCPT ); Sun, 2 Jun 2019 17:02:27 -0400 Received: by mail-io1-f46.google.com with SMTP id n5so12645942ioc.7 for ; Sun, 02 Jun 2019 14:02:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=HC8vtrRsh50Ohc3EaIB0NoebMSo23njywbCwxitxUSo=; b=G05oV6yGANfGUrsafNDMFdY+sdiwhud8O9hlc5blEpxavx9e8NMec2fjDyxse4N94X 2a89tU71cAzexNCkHgP9PRg5MZKqWwfvM5tdRQOUzBE+IVLhk0nxFDg1nKUAGhNgYJWK OTOxrwoH4oo/4pDSoZ0Fkojiw/sCTsCbJPv9w= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=HC8vtrRsh50Ohc3EaIB0NoebMSo23njywbCwxitxUSo=; b=FTcHSl3nz+Mv/4Y4+d9/gYI1rRZ+WQNXh90HXKh+RXO2KnqFXo7NwwkKtt+1dkD9Nq xJUrptdw+ZShPAr2JpKwDmu90j/ZbEgyvbVo9Gc+3/tYYxD1axCadeXmatunPPzXtqKs sKAtla7cWGzxrZFHGDkGxhwAKuhtsRNf4wVBcnShf6ayuyWix1HqADowMFTQgr/9zgir SeqvrHUIbSlX59+JdhYSmUhwDCd5ypb9XvHHFMdiIg6wrIa78q6De8VxS5IYprUsqJ0m Dnjrkn8+I0cZrCCT/eik+EqHgAIv10j0pOC++1mdxcrnHVoIuJcVc4Yl2Ei2pHBVriUG z4RA== X-Gm-Message-State: APjAAAWJTlj5Iz4C1Huov3XRjiX3jZmnTdAgKHX0abaQliuMRkqGUBTs rbUTgc6ZCwY4XNdG5UPtuj1dpwUGSK8= X-Google-Smtp-Source: APXvYqxlnw73pTZ9X3LGfQhk4wHkxDI22S6dISiA1Mrh1rHUWpFhM8Ynp9JwrYuQPTbxTvYWg9PiIA== X-Received: by 2002:a05:6602:2285:: with SMTP id d5mr14055239iod.196.1559509346192; Sun, 02 Jun 2019 14:02:26 -0700 (PDT) Received: from mail-it1-f171.google.com (mail-it1-f171.google.com. [209.85.166.171]) by smtp.gmail.com with ESMTPSA id y18sm4154690iob.64.2019.06.02.14.02.25 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 02 Jun 2019 14:02:26 -0700 (PDT) Received: by mail-it1-f171.google.com with SMTP id n189so5150651itd.0 for ; Sun, 02 Jun 2019 14:02:25 -0700 (PDT) X-Received: by 2002:a24:5652:: with SMTP id o79mr15076656itb.164.1559508868756; Sun, 02 Jun 2019 13:54:28 -0700 (PDT) MIME-Version: 1.0 References: <20150910005708.GA23369@wfg-t540p.sh.intel.com> <20150910102513.GA1677@fixme-laptop.cn.ibm.com> <20150910171649.GE4029@linux.vnet.ibm.com> <20150911021933.GA1521@fixme-laptop.cn.ibm.com> <20150921193045.GA13674@lerouge> <20150921204327.GH4029@linux.vnet.ibm.com> <20190602055607.bk5vgmwjvvt4wejd@gondor.apana.org.au> In-Reply-To: <20190602055607.bk5vgmwjvvt4wejd@gondor.apana.org.au> From: Linus Torvalds Date: Sun, 2 Jun 2019 13:54:12 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: rcu_read_lock lost its compiler barrier To: Herbert Xu Cc: "Paul E. McKenney" , Frederic Weisbecker , Boqun Feng , Fengguang Wu , LKP , LKML , Netdev , "David S. Miller" Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jun 1, 2019 at 10:56 PM Herbert Xu wrote: > > You can't then go and decide to remove the compiler barrier! To do > that you'd need to audit every single use of rcu_read_lock in the > kernel to ensure that they're not depending on the compiler barrier. What's the possible case where it would matter when there is no preemption? Linus