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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 93D7BC33CA1 for ; Mon, 20 Jan 2020 08:19:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6AFBE207E0 for ; Mon, 20 Jan 2020 08:19:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="K242n6o0" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726587AbgATITW (ORCPT ); Mon, 20 Jan 2020 03:19:22 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:41770 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726039AbgATITW (ORCPT ); Mon, 20 Jan 2020 03:19:22 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Transfer-Encoding :Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=lv6mWV+LyBEpHARixm1MrWLqdXwoOkowEDIcmQHZnc0=; b=K242n6o0jAV2chrAfUWM2qOEKD pFQAkqMOBGF2gB/c3h630UEUAffnHDCcvHqDGASyUzUxxwxVonblqWWaxvJLxo1i9mWVjyV6EXhPA uuJ0WhRJF9qk1mpJr29Wc4Hc7MCk/5Uxiz1/8/RLWNPGOLGa84F+8ITD4QwvLQHFht++tuq1qgIfr yOEGRW5/dfMp3nr6gLe+9Tv9boTVIcYaMzjQnaqslvThV91NI7g2SBBLCgUJAjDk/fM5+GL75tcq6 Q8yJi9r7l33dJnKA0zy1gFENHyr2RK4WUdiRw0qik1sGeWRnA24SD9DAWA1GuBMR1jEg+V/hi3mFc kUDCsnVQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1itSH2-0007Y6-TP; Mon, 20 Jan 2020 08:19:05 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 634EC3035D4; Mon, 20 Jan 2020 09:17:20 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 936C820983E34; Mon, 20 Jan 2020 09:18:58 +0100 (CET) Date: Mon, 20 Jan 2020 09:18:58 +0100 From: Peter Zijlstra To: Eric Dumazet Cc: Arvind Sankar , 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 Subject: Re: [PATCH] net: optimize cmpxchg in ip_idents_reserve Message-ID: <20200120081858.GI14879@hirez.programming.kicks-ass.net> References: <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> <94573cea-a833-9b48-6581-8cc5cdd19b89@gmail.com> <20200117183800.GA2649345@rani.riverdale.lan> <45224c36-9941-aae5-aca4-e2c8e3723355@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <45224c36-9941-aae5-aca4-e2c8e3723355@gmail.com> 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 On Fri, Jan 17, 2020 at 10:48:19AM -0800, Eric Dumazet wrote: > > > On 1/17/20 10:38 AM, Arvind Sankar wrote: > > On Fri, Jan 17, 2020 at 10:16:45AM -0800, Eric Dumazet wrote: > >> 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. > >> > > > > No, it was bumped in 2018 in commit cafa0010cd51 ("Raise the minimum > > required gcc version to 4.6"). That raised it from 3.2 -> 4.6. > > > > This seems good to me, for gcc at least. > > Maybe it is time to enfore -fno-strict-overflow in KBUILD_CFLAGS > instead of making it conditional. IIRC there was a bug in UBSAN vs -fwrapv/-fno-strict-overflow that was only fixed in gcc-8 or 9 or so. So while the -fwrapv/-fno-strict-overflow flag has been correctly supported since like forever, UBSAN was buggy until quite recent when used in conjustion with that flag.