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=-5.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 06214C33C9E for ; Fri, 17 Jan 2020 18:16:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D4EAA2082F for ; Fri, 17 Jan 2020 18:16:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="XAwhFczp" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729014AbgAQSQs (ORCPT ); Fri, 17 Jan 2020 13:16:48 -0500 Received: from mail-pf1-f193.google.com ([209.85.210.193]:33750 "EHLO mail-pf1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726603AbgAQSQs (ORCPT ); Fri, 17 Jan 2020 13:16:48 -0500 Received: by mail-pf1-f193.google.com with SMTP id z16so12318889pfk.0; Fri, 17 Jan 2020 10:16:47 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=aD0tuQOOzQ4oPbILPoDAiI6G2Z70ung0n+DSdMMnNJM=; b=XAwhFczp0KmF7S4+mP+LKpuEITPW8TFrYJjFMPDvKsfwAhoGkynU29aeT7ZqFXq1u7 gVDBjYq8rj1+xwysNNi4G/44MygeUidK4BAC2uI4Ql20Wr2SRsWeirad2G4ygoaU+qIq zQccKK++5t95MmYnFfwAQb8HAZz+3HjAGkOWGyZ6hMfaKAR2MFL690nGCkZZdO56LoSj wjT2dLaloYNNswOOdL322gcruh2L6yUWgp6eL2VohufB2R0dlg9nZUhi+2fpetFEX+Rm GkVJY7CVN2swKSsvPBu0/h4L40vTxHjGYa6t+aAbCILTSKRl3zVO/4W+XhSDCSI7OPrV 70ew== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=aD0tuQOOzQ4oPbILPoDAiI6G2Z70ung0n+DSdMMnNJM=; b=R/HclvEcSkKUb6D87T+EuyhpHZ1pad/q8rhHisvrMHSlEwg9IAVgwr5IJsCaXCWDI8 +8UFJk65gwu0ReyUoO13flbqhUnsnIMyjSxMiaXn9dpHc6Mc3xSvKilYFJq8MKlV4QI/ Tj4i+tbk83IvIYdUn7HOa0E1jXdNs6e8EO+Tj3EvXfhy8TDOEY7aFK/+nMlAM3+Ta7PZ 6G1SV609cHK13XPRGXY8UdDbvJGaQEldEhxyvZ43YPQ7sZsbemvO5OOhCR3vZ5fmJT7v G7ii50Gz7GorxshjljFvUESxsHiABnl8qkbzYCntJRWB6w17sTxZWzaioaHLayXnEj2R diCA== X-Gm-Message-State: APjAAAUZ2RfkeCdlInVp7sI4yTUKPXHaULeKvpOP6XnlqDgO/TwE2Hxl ZmTRyPNQd2W+fu5MYRZaVE8= X-Google-Smtp-Source: APXvYqwmqpjSoPfBdcrHSDgt2evoaybgY+qpc04lufY7AQGAgKNpGRqu1fs3w6huCAqrB5q65VH6hg== X-Received: by 2002:a63:1204:: with SMTP id h4mr45519701pgl.288.1579285007532; Fri, 17 Jan 2020 10:16:47 -0800 (PST) Received: from [192.168.86.235] (c-73-241-150-58.hsd1.ca.comcast.net. [73.241.150.58]) by smtp.gmail.com with ESMTPSA id q63sm30965322pfb.149.2020.01.17.10.16.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 17 Jan 2020 10:16:46 -0800 (PST) Subject: Re: [PATCH] net: optimize cmpxchg in ip_idents_reserve To: Arvind Sankar , Eric Dumazet Cc: Peter Zijlstra , Shaokun Zhang , David Miller , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, jinyuqi@huawei.com, kuznet@ms2.inr.ac.ru, yoshfuji@linux-ipv6.org, edumazet@google.com, guoyang2@huawei.com, Will Deacon References: <1579058620-26684-1-git-send-email-zhangshaokun@hisilicon.com> <20200116.042722.153124126288244814.davem@davemloft.net> <930faaff-4d18-452d-2e44-ef05b65dc858@gmail.com> <1b3aaddf-22f5-1846-90f1-42e68583c1e4@gmail.com> <430496fc-9f26-8cb4-91d8-505fda9af230@hisilicon.com> <20200117123253.GC14879@hirez.programming.kicks-ass.net> <7e6c6202-24bb-a532-adde-d53dd6fb14c3@gmail.com> <20200117180324.GA2623847@rani.riverdale.lan> From: Eric Dumazet Message-ID: <94573cea-a833-9b48-6581-8cc5cdd19b89@gmail.com> Date: Fri, 17 Jan 2020 10:16:45 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: <20200117180324.GA2623847@rani.riverdale.lan> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 1/17/20 10:03 AM, Arvind Sankar wrote: > On Fri, Jan 17, 2020 at 08:35:07AM -0800, Eric Dumazet wrote: >> >> >> On 1/17/20 4:32 AM, Peter Zijlstra wrote: >> >>> >>> That's crazy, just accept that UBSAN is taking bonghits and ignore it. >>> Use atomic_add_return() unconditionally. >>> >> >> Yes, we might simply add a comment so that people do not bug us if >> their compiler is too old. >> >> /* If UBSAN reports an error there, please make sure your compiler >> * supports -fno-strict-overflow before reporting it. >> */ >> return atomic_add_return(segs + delta, p_id) - segs; >> > > Do we need that comment any more? The flag was apparently introduced in > gcc-4.2 and we only support 4.6+ anyway? Wasńt it the case back in 2016 already for linux-4.8 ? What will prevent someone to send another report to netdev/lkml ? -fno-strict-overflow support is not a prereq for CONFIG_UBSAN. Fact that we kept in lib/ubsan.c and lib/test_ubsan.c code for test_ubsan_add_overflow() and test_ubsan_sub_overflow() is disturbing. commit adb03115f4590baa280ddc440a8eff08a6be0cb7 Author: Eric Dumazet Date: Tue Sep 20 18:06:17 2016 -0700 net: get rid of an signed integer overflow in ip_idents_reserve() Jiri Pirko reported an UBSAN warning happening in ip_idents_reserve() [] UBSAN: Undefined behaviour in ./arch/x86/include/asm/atomic.h:156:11 [] signed integer overflow: [] -2117905507 + -695755206 cannot be represented in type 'int' Since we do not have uatomic_add_return() yet, use atomic_cmpxchg() so that the arithmetics can be done using unsigned int. Fixes: 04ca6973f7c1 ("ip: make IP identifiers less predictable") Signed-off-by: Eric Dumazet Reported-by: Jiri Pirko Signed-off-by: David S. Miller