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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 D0782C432C0 for ; Tue, 3 Dec 2019 19:58:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A4AC42073F for ; Tue, 3 Dec 2019 19:58:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727457AbfLCT6U (ORCPT ); Tue, 3 Dec 2019 14:58:20 -0500 Received: from shards.monkeyblade.net ([23.128.96.9]:52058 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726564AbfLCT6T (ORCPT ); Tue, 3 Dec 2019 14:58:19 -0500 Received: from localhost (unknown [IPv6:2601:601:9f00:1c3::3d5]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) (Authenticated sender: davem-davemloft) by shards.monkeyblade.net (Postfix) with ESMTPSA id BA0EE1510CE16; Tue, 3 Dec 2019 11:58:18 -0800 (PST) Date: Tue, 03 Dec 2019 11:58:18 -0800 (PST) Message-Id: <20191203.115818.1902434596879929857.davem@davemloft.net> To: liuhangbin@gmail.com Cc: netdev@vger.kernel.org, ja@ssi.bg, marcelo.leitner@gmail.com, dsahern@gmail.com, edumazet@google.com Subject: Re: [PATCHv2 net] ipv6/route: should not update neigh confirm time during PMTU update From: David Miller In-Reply-To: <20191203102534.GK18865@dhcp-12-139.nay.redhat.com> References: <20191202.184704.723174427717421022.davem@davemloft.net> <20191203101536.GJ18865@dhcp-12-139.nay.redhat.com> <20191203102534.GK18865@dhcp-12-139.nay.redhat.com> X-Mailer: Mew version 6.8 on Emacs 26.1 Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.12 (shards.monkeyblade.net [149.20.54.216]); Tue, 03 Dec 2019 11:58:19 -0800 (PST) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: Hangbin Liu Date: Tue, 3 Dec 2019 18:25:35 +0800 > > Hi David, > On Tue, Dec 03, 2019 at 06:15:36PM +0800, Hangbin Liu wrote: >> On Mon, Dec 02, 2019 at 06:47:04PM -0800, David Miller wrote: >> > From: Hangbin Liu >> > Date: Tue, 3 Dec 2019 10:11:37 +0800 >> > >> > > Fix it by removing the dst_confirm_neigh() in __ip6_rt_update_pmtu() as >> > > there is no two-way communication during PMTU update. >> > > >> > > v2: remove dst_confirm_neigh directly as David Miller pointed out. >> > >> > That's not what I said. >> > >> > I said that this interface is designed for situations where the neigh >> > update is appropriate, and that's what happens for most callers _except_ >> > these tunnel cases. >> > >> > The tunnel use is the exception and invoking the interface >> > inappropriately. >> > >> > It is important to keep the neigh reachability fresh for TCP flows so >> > you cannot remove this dst_confirm_neigh() call. > > I have one question here. Since we have the .confirm_neigh fuction in > struct dst_ops. How about do a dst->ops->confirm_neigh() separately after > dst->ops->update_pmtu()? Why should we mix the confirm_neigh() in > update_pmtu(), like ip6_rt_update_pmtu()? Two indirect calls which have high cost due to spectre mitigation?