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=-2.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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 CF10FC433E0 for ; Thu, 28 Jan 2021 01:40:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7D82164DCE for ; Thu, 28 Jan 2021 01:40:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231440AbhA1Bk3 (ORCPT ); Wed, 27 Jan 2021 20:40:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47436 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231377AbhA1Bjx (ORCPT ); Wed, 27 Jan 2021 20:39:53 -0500 Received: from mail-pj1-x102f.google.com (mail-pj1-x102f.google.com [IPv6:2607:f8b0:4864:20::102f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AA7A8C061573; Wed, 27 Jan 2021 17:38:56 -0800 (PST) Received: by mail-pj1-x102f.google.com with SMTP id p15so2912656pjv.3; Wed, 27 Jan 2021 17:38:56 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=mhj94VplAFkADQfm7BXxj5A1TW1GeKrFb8pkt/UHLlo=; b=NZO020QXNtYDc4PTbzqPCFpYJQy0RYANuzcRyVB9u/s6BMK/fGUB4ejWb2+tBKJYgE h2KOusHIU8giTq4BgXMUzucQFLZmg4sm1M3T2w9Z9MuIp0m/ZGrV1N7CRImRf60BXgaS 8kbCAtsREpDW4V650VdxJIzr6GCAmg1bBcmMnQ75cAQPsEQoZ4xoKmqtzdNoR+ZeGALv rik77Ik/Ao0DBEE2TnTH4w/xkUqLFxNNmZ+DoF6IyK6OWnh4wjNsXDe6f7n6RTQYhp4w j6IeNTSDepsq7jdjTgWiDw0GMYMGswzNMyIOYDfV91xwHPM7TvC45buWJjBolUGLOyFt FmIw== 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=mhj94VplAFkADQfm7BXxj5A1TW1GeKrFb8pkt/UHLlo=; b=n0TLn8LGeF2OlKs9iaWEwzPjYBAi2sLBcutYvRL2SjboQx846ugy5nH6GMqdbuGteV vXprk964JVmGfDFr3N/39IKujgK+ipxwh9yWtcoYgeAYN/cQB8FBpPG3KXCNdKXJGNNs Zu5uPnjCUBH591QZiBTFwIVM3OkNMEm9FKmbJdLUeRTBVKIIoyBX6IcWjjLUzakUnYJ3 s6XnTG/ogAZ8X/awIjqlAyCiJCVJQXyY1gngeo4ksn8XsvFu8hZo2QAadq/lls3dFxUy 1/9AwAqWQ1bln5lsojN1Cl1O2+uEQgJbOzd18Yw0huY7ZrG2MfWkVxp51wHtHKUJRv08 tpdQ== X-Gm-Message-State: AOAM530sHokyOXhcNO1xzA2nEuscxFtoHO0gGrrmKgw5d6lGFyqNATMy VODRT8uXQjKZFa2o2xm6HK5ZTsgQg8fM4GRN0AC38+36Qcssdw== X-Google-Smtp-Source: ABdhPJxdzuuOQjc4/lTsSK3XjKXtdKFUFZjKJ6Bi17WmwFbXt++FSnSVg7++TFCMO/7S+td0Hf7tXHZG3TybaGbpF+I= X-Received: by 2002:a17:90a:f98c:: with SMTP id cq12mr8495343pjb.191.1611797936230; Wed, 27 Jan 2021 17:38:56 -0800 (PST) MIME-Version: 1.0 References: <20210127165602.610b10c0@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> In-Reply-To: <20210127165602.610b10c0@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> From: Cong Wang Date: Wed, 27 Jan 2021 17:38:44 -0800 Message-ID: Subject: Re: BUG: Incorrect MTU on GRE device if remote is unspecified To: Jakub Kicinski Cc: Slava Bacherikov , Willem de Bruijn , open list , Linux Kernel Network Developers , Xie He Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 27, 2021 at 4:56 PM Jakub Kicinski wrote: > > On Mon, 25 Jan 2021 22:10:10 +0200 Slava Bacherikov wrote: > > Hi, I'd like to report a regression. Currently, if you create GRE > > interface on the latest stable or LTS kernel (5.4 branch) with > > unspecified remote destination it's MTU will be adjusted for header size > > twice. For example: > > > > $ ip link add name test type gre local 127.0.0.32 > > $ ip link show test | grep mtu > > 27: test@NONE: mtu 1452 qdisc noop state DOWN mode DEFAULT group > > default qlen 1000 > > > > or with FOU > > > > $ ip link add name test2 type gre local 127.0.0.32 encap fou > > encap-sport auto encap-dport 6666 > > $ ip link show test2 | grep mtu > > 28: test2@NONE: mtu 1436 qdisc noop state DOWN mode DEFAULT > > group default qlen 1000 > > > > The same happens with GUE too (MTU is 1428 instead of 1464). > > As you can see that MTU in first case is 1452 (1500 - 24 - 24) and with > > FOU it's 1436 (1500 - 32 - 32), GUE 1428 (1500 - 36 - 36). If remote > > address is specified MTU is correct. > > > > This regression caused by fdafed459998e2be0e877e6189b24cb7a0183224 commit. > > Cong is this one on your radar? Yeah, I guess ipgre_link_update() somehow gets called twice, but I will need to look into it. Thanks.