From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shmulik Ladkani Subject: Re: [PATCH net v3] ipv4: allow local fragmentation in ip_finish_output_gso() Date: Thu, 3 Nov 2016 22:27:51 +0200 Message-ID: <20161103222751.5ae120ed@halley> References: <1478118977-19608-1-git-send-email-lrichard@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, jtluka@redhat.com To: Lance Richardson , fw@strlen.de, hannes@stressinduktion.org Return-path: Received: from mail-wm0-f65.google.com ([74.125.82.65]:34516 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750970AbcKCU2C (ORCPT ); Thu, 3 Nov 2016 16:28:02 -0400 Received: by mail-wm0-f65.google.com with SMTP id p190so749533wmp.1 for ; Thu, 03 Nov 2016 13:28:02 -0700 (PDT) In-Reply-To: <1478118977-19608-1-git-send-email-lrichard@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: Hi Hannes, Lance, On Wed, 2 Nov 2016 16:36:17 -0400 Lance Richardson wrote: > > - if (skb_iif && !(df & htons(IP_DF))) { > - /* Arrived from an ingress interface, got encapsulated, with > - * fragmentation of encapulating frames allowed. > - * If skb is gso, the resulting encapsulated network segments > - * may exceed dst mtu. > - * Allow IP Fragmentation of segments. > - */ > - IPCB(skb)->flags |= IPSKB_FRAG_SEGS; > - } Thinking this over, I'm concerned of this change. Few months back, we discussed this and got to the conclusion that in the "ingress,tunnel,egress" scenario, segments are allowed to be fragmented if the original inner ip packet does NOT have the DF. See https://patchwork.ozlabs.org/patch/657132/ https://patchwork.ozlabs.org/patch/661219/ I think you expressed that those tunneled skbs already having DF set should go through pmtu discovery. Suggested patch unconditionally calls skb_gso_validate_mtu(). Thus we're changing behavior for "ingress,tunnel,egress" scenario of the tunneled packets having DF set in the inner iph. WDYT?