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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3C8C6C0015E for ; Thu, 20 Jul 2023 18:54:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229863AbjGTSyR (ORCPT ); Thu, 20 Jul 2023 14:54:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48068 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229633AbjGTSyP (ORCPT ); Thu, 20 Jul 2023 14:54:15 -0400 Received: from mail-pl1-x635.google.com (mail-pl1-x635.google.com [IPv6:2607:f8b0:4864:20::635]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B81C01705; Thu, 20 Jul 2023 11:54:14 -0700 (PDT) Received: by mail-pl1-x635.google.com with SMTP id d9443c01a7336-1bb1baf55f5so8534535ad.0; Thu, 20 Jul 2023 11:54:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20221208; t=1689879254; x=1690484054; h=to:cc:date:message-id:subject:mime-version :content-transfer-encoding:from:from:to:cc:subject:date:message-id :reply-to; bh=fRq4kiOe6o3GCeNturgO6VEAqY0DWx/wr2Uqp7KCQAQ=; b=fNQQbA+N7NG8ROfS0eyXZ4nfFd3AwMKZfpfL9lXlvgIkkHfN/3GoQG+tX3ehHsb8dv wGbxzGoTR581bIPQCfdzJRLm4LeVfm9Kcticw1Jd0mlKfxKfL47vahmEoZ0aeo26qApz tZw3W7WeCo6PYtJqfPkdXYpRjSQjKdveHSHQQZtG5SJWaAtwAVzUxskYt9VVOPmYHvSG m1nLU7HpvcwZCmHKeGfG5qQqvww+eezcjosiQfsJwq9VLeZcPENHUXXbttAxdxyunlqn 0BfdyhYgOUXAij8+5K7/S1BnN2NrWmPUopT0O824l7MoAqrIqkvPPgIVsp1KGXvkbFSi mmmg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1689879254; x=1690484054; h=to:cc:date:message-id:subject:mime-version :content-transfer-encoding:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=fRq4kiOe6o3GCeNturgO6VEAqY0DWx/wr2Uqp7KCQAQ=; b=dvcQo+LFj/gEuYAscUDRHnP9nczYY0lOsYfIZ9mZ5/3rrV6ZjRWIzHep0O7QdkrcZx wJmJgofE4C/IwZTUoXtlMfIlHYPfqLNaMn8DFpHe3dGRKMh6EjUQeVCrDr4dmKWbdI5k GAb3qbnLKyfB7qdIo8Wk+TPUWNk7pd2kPUYJN23KInQhlnKh4lLGdNjq0Z0jLJvJOkyL W3OHOvlOtFfKD8cvmyFIXfotuAWEWM0npOrUm53xy6fvtwmSoIFZkyCiUzV2eZ8wtqhA FrnT62qQNVDOsvrMUTJC3u2DPGcx+92ECRgDt2IrVjV1SssHyR2LUeDFBiezmQeXMYyC ibuQ== X-Gm-Message-State: ABy/qLZTKEzPM68atkk/5TAG/+4SWFWTWyVAZdf7OTCMHLhXmn4uOI75 tv7LyNDktqEjOzKhnwD47ogLwwtT9P0= X-Google-Smtp-Source: APBJJlHzuCcODyNyT6KQ00oY5CFkyrzoStrZfVAbxsa0cZRpGI+a0UvG2ODhZLQ/Id7StLYc9sd8Lg== X-Received: by 2002:a17:902:e883:b0:1b9:de75:d5bb with SMTP id w3-20020a170902e88300b001b9de75d5bbmr217104plg.7.1689879253780; Thu, 20 Jul 2023 11:54:13 -0700 (PDT) Received: from smtpclient.apple ([2402:d0c0:2:a2a::1]) by smtp.gmail.com with ESMTPSA id n7-20020a170902d2c700b001b9c960ff9bsm1762792plc.78.2023.07.20.11.54.09 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 20 Jul 2023 11:54:13 -0700 (PDT) From: Alan Huang Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3731.400.51.1.1\)) Subject: Question about the barrier() in hlist_nulls_for_each_entry_rcu() Message-Id: <04C1E631-725C-47AD-9914-25D5CE04DFF4@gmail.com> Date: Fri, 21 Jul 2023 02:53:53 +0800 Cc: "Paul E. McKenney" , Eric Dumazet , roman.gushchin@linux.dev To: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, rcu@vger.kernel.org X-Mailer: Apple Mail (2.3731.400.51.1.1) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, I noticed a commit c87a124a5d5e(=E2=80=9Cnet: force a reload of first = item in hlist_nulls_for_each_entry_rcu=E2=80=9D) and a related discussion [1]. After reading the whole discussion, it seems like that ptr->field was = cached by gcc even with the deprecated ACCESS_ONCE(), so my question is: Is that a compiler bug? If so, has this bug been fixed today, = ten years later?=20 =09 What about READ_ONCE(ptr->field)? [1] = https://lore.kernel.org/all/1369699930.3301.494.camel@edumazet-glaptop/ Thanks, Alan=