From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH net] net: Correctly set segment mac_len in skb_segment(). Date: Thu, 31 Jul 2014 22:29:12 -0700 (PDT) Message-ID: <20140731.222912.1916841568774711697.davem@davemloft.net> References: <1406817186-17844-1-git-send-email-vyasevic@redhat.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, edumazet@google.com To: vyasevic@redhat.com Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:54472 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750851AbaHAF3N (ORCPT ); Fri, 1 Aug 2014 01:29:13 -0400 In-Reply-To: <1406817186-17844-1-git-send-email-vyasevic@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: From: Vlad Yasevich Date: Thu, 31 Jul 2014 10:33:06 -0400 > When performing segmentation, the mac_len value is copied right > out of the original skb. However, this value is not always set correctly > (like when the packet is VLAN-tagged) and we'll end up copying a bad > value. > > One way to demonstrate this is to configure a VM which tags > packets internally and turn off VLAN acceleration on the forwarding > bridge port. The packets show up corrupt like this: > 16:18:24.985548 52:54:00:ab:be:25 > 52:54:00:26:ce:a3, ethertype 802.1Q > (0x8100), length 1518: vlan 100, p 0, ethertype 0x05e0, > 0x0000: 8cdb 1c7c 8cdb 0064 4006 b59d 0a00 6402 ...|...d@.....d. > 0x0010: 0a00 6401 9e0d b441 0a5e 64ec 0330 14fa ..d....A.^d..0.. > 0x0020: 29e3 01c9 f871 0000 0101 080a 000a e833)....q.........3 > 0x0030: 000f 8c75 6e65 7470 6572 6600 6e65 7470 ...unetperf.netp > 0x0040: 6572 6600 6e65 7470 6572 6600 6e65 7470 erf.netperf.netp > 0x0050: 6572 6600 6e65 7470 6572 6600 6e65 7470 erf.netperf.netp > 0x0060: 6572 6600 6e65 7470 6572 6600 6e65 7470 erf.netperf.netp > ... > > This also leads to awful throughput as GSO packets are dropped and > cause retransmissions. > > The solution is to set the mac_len using the values already available > in then new skb. We've already adjusted all of the header offset, so we > might as well correctly figure out the mac_len using skb_reset_mac_len(). > After this change, packets are segmented correctly and performance > is restored. > > CC: Eric Dumazet > Signed-off-by: Vlad Yasevich Applied, and I'm assuming this is meant to go to -stable too right?