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 EEAD9C433F5 for ; Sat, 16 Apr 2022 06:56:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229691AbiDPG7J (ORCPT ); Sat, 16 Apr 2022 02:59:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54192 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229445AbiDPG7I (ORCPT ); Sat, 16 Apr 2022 02:59:08 -0400 Received: from mail-qk1-x734.google.com (mail-qk1-x734.google.com [IPv6:2607:f8b0:4864:20::734]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 183B715FC5; Fri, 15 Apr 2022 23:56:38 -0700 (PDT) Received: by mail-qk1-x734.google.com with SMTP id e10so7960933qka.6; Fri, 15 Apr 2022 23:56:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=punmqzR82m/ivhuuKbOeeSpij9rdVwj6dBLRCcjDN2k=; b=i9cqRmdeTs/dXZI7D8kVcvX7nKhAwVdRcsrrwV0udpeEz8u7vILSkXeM6Y4ILBwLw8 8vo5kZ1OpuvzjvqTf1HFeDTKoIjZ3dPKmhQboel8qI974hmxHwWLFUgsJNBUVEjw+Tc6 kL2AsD9EAsTN+etwV5KUcpvxVUXCVNLj7No/z6ySWd/UQPvsJXld/Ne2ur4Qh5dZkDMs NVMTGlHHChISbR5xF6QAxi1kd9sFXWZxFSvDrV+fzbtmH4ROgYXbxibN+7iaiBKKMlo7 csRB5we2ap8f6joUB0iF3pPQT1DiNQCDPjN73JxXkn/llWZ2F5PBI5wzgrcfeC3Jkjmb uaqg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=punmqzR82m/ivhuuKbOeeSpij9rdVwj6dBLRCcjDN2k=; b=d9YExKATJmhUa09dPHJ6Zmh2X3Dg+7fJZ4rHiZNQMVK++ND8lNUV91qrN7+RJSjat5 AMeM6xFXjyuvTwUJupKy8iO71JvPrahGF0S1kKV5WpK08H+UPVS1jD1V3eAy4OwNDUVC OyF949SW77fTndSDnBNfhvyyqH0CfvSSTnD+RCGMAAIB8VBAJ0tF2JOL2u03YCWr2Hem KsPyDVfG90k+g1Jf3DP5YUblO3sGiwQgIEXOQvRsA0aXGix54qMROc26sPUi/w9EUA7a oFUmPl3PTRdm4pMNxAed6lrAuaUE7A/qxhRxpJenevJUrCNy6ESKnG8IdFGN1VtDOscV oNlw== X-Gm-Message-State: AOAM532Udbm/PoQV6QYLG3oULQK7xiscRQNbniZpbnPH/e6s/AUkCk6t RxaX/RRC6uTmwXE3If8gDQ== X-Google-Smtp-Source: ABdhPJze666BWXOZ7v9o1b6NG80dduEFjgHheOq3DDDAfADinL6HdmzmCwEKN6ASVTQtu2Maih3mqA== X-Received: by 2002:a05:620a:bd4:b0:47b:4c75:894e with SMTP id s20-20020a05620a0bd400b0047b4c75894emr1303721qki.425.1650092197189; Fri, 15 Apr 2022 23:56:37 -0700 (PDT) Received: from bytedance (ec2-13-57-97-131.us-west-1.compute.amazonaws.com. [13.57.97.131]) by smtp.gmail.com with ESMTPSA id d8-20020ac85d88000000b002f18ecfd221sm4087252qtx.82.2022.04.15.23.56.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 15 Apr 2022 23:56:36 -0700 (PDT) Date: Fri, 15 Apr 2022 23:56:33 -0700 From: Peilin Ye To: Jakub Kicinski Cc: "David S. Miller" , Hideaki YOSHIFUJI , David Ahern , Peilin Ye , Cong Wang , Feng Zhou , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net 2/2] ip6_gre: Fix skb_under_panic in __gre6_xmit() Message-ID: <20220416065633.GA10882@bytedance> References: <9cd9ca4ac2c19be288cb8734a86eb30e4d9e2050.1649715555.git.peilin.ye@bytedance.com> <20220414131424.744aa842@kernel.org> <20220414200854.GA2729@bytedance> <20220415191133.0597a79a@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220415191133.0597a79a@kernel.org> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Fri, Apr 15, 2022 at 07:11:33PM +0200, Jakub Kicinski wrote: > On Thu, 14 Apr 2022 13:08:54 -0700 Peilin Ye wrote: > > > We should also reject using SEQ with collect_md, but that's a separate > > > issue. > > > > Could you explain this a bit more? It seems that commit 77a5196a804e > > ("gre: add sequence number for collect md mode.") added this > > intentionally. > > Interesting. Maybe a better way of dealing with the problem would be > rejecting SEQ if it's not set on the device itself. According to ip-link(8), the 'external' option is mutually exclusive with the '[o]seq' option. In other words, a collect_md mode IP6GRETAP device should always have the TUNNEL_SEQ flag off in its 'tunnel->parms.o_flags'. (However, I just tried: $ ip link add dev ip6gretap11 type ip6gretap oseq external ^^^^ ^^^^^^^^ ...and my 'ip' executed it with no error. I will take a closer look at iproute2 later; maybe it's undefined behavior...) How about: 1. If 'external', then 'oseq' means "always turn off NETIF_F_LLTX, so it's okay to set TUNNEL_SEQ in e.g. eBPF"; 2. Otherwise, if 'external' but NOT 'oseq', then whenever we see a TUNNEL_SEQ in skb's tunnel info, we do something like WARN_ONCE() then return -EINVAL. ? > When the device is set up without the SEQ bit enabled it disables Tx > locking (look for LLTX). This means that multiple CPUs can try to do > the tunnel->o_seqno++ in parallel. Not catastrophic but racy for sure. Thanks for the explanation! At first glance, I was wondering why don't we make 'o_seqno' atomic until I found commit b790e01aee74 ("ip_gre: lockless xmit"). I quote: """ Even using an atomic_t o_seq, we would increase chance for packets being out of order at receiver. """ I don't fully understand this out-of-order yet, but it seems that making 'o_seqno' atomic is not an option? Thanks, Peilin Ye