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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 04C07C282D0 for ; Tue, 29 Jan 2019 06:04:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D05A92177E for ; Tue, 29 Jan 2019 06:04:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727347AbfA2GEq (ORCPT ); Tue, 29 Jan 2019 01:04:46 -0500 Received: from szxga06-in.huawei.com ([45.249.212.32]:54782 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726314AbfA2GEp (ORCPT ); Tue, 29 Jan 2019 01:04:45 -0500 Received: from DGGEMS404-HUB.china.huawei.com (unknown [172.30.72.59]) by Forcepoint Email with ESMTP id A03147361EA0CCB011CD; Tue, 29 Jan 2019 14:04:43 +0800 (CST) Received: from [127.0.0.1] (10.177.96.96) by DGGEMS404-HUB.china.huawei.com (10.3.19.204) with Microsoft SMTP Server id 14.3.408.0; Tue, 29 Jan 2019 14:04:41 +0800 Subject: Re: [PATCH net-next] net: udp Allow CHECKSUM_UNNECESSARY packets to do GRO. To: Tom Herbert References: <1548214428-114642-1-git-send-email-maowenan@huawei.com> CC: Linux Kernel Network Developers , "David S. Miller" , Eric Dumazet From: maowenan Message-ID: <038cf844-ca2f-8db2-7ed6-fee39cbcfc7d@huawei.com> Date: Tue, 29 Jan 2019 14:04:40 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.177.96.96] X-CFilter-Loop: Reflected Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2019/1/29 12:01, Tom Herbert wrote: > On Mon, Jan 28, 2019 at 7:00 PM maowenan wrote: >> >> Hi all， >> Do you have any comments about this change? >> >> >> On 2019/1/23 11:33, Mao Wenan wrote: >>> When udp4_gro_receive() get one packet that uh->check=0, >>> skb_gro_checksum_validate_zero_check() will set the >>> skb->ip_summed = CHECKSUM_UNNECESSARY; >>> skb->csum_level = 0; >>> Then udp_gro_receive() will flush the packet which is not CHECKSUM_PARTIAL, >>> It is not our expect, because check=0 in udp header indicates this >>> packet is no need to caculate checksum, we should go further to do GRO. >>> >>> This patch changes the value of csum_cnt according to skb->csum_level. >>> --- >>> include/linux/netdevice.h | 1 + >>> 1 file changed, 1 insertion(+) >>> >>> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h >>> index 1377d08..9c819f1 100644 >>> --- a/include/linux/netdevice.h >>> +++ b/include/linux/netdevice.h >>> @@ -2764,6 +2764,7 @@ static inline void skb_gro_incr_csum_unnecessary(struct sk_buff *skb) >>> * during GRO. This saves work if we fallback to normal path. >>> */ >>> __skb_incr_checksum_unnecessary(skb); >>> + NAPI_GRO_CB(skb)->csum_cnt = skb->csum_level + 1; > > That doesn't look right. This would be reinitializing the GRO > checksums from the beginning. > >>> } >>> } >>> >>> >> > I assume the code is bailing on this conditional: > > if (NAPI_GRO_CB(skb)->encap_mark || > (skb->ip_summed != CHECKSUM_PARTIAL && > NAPI_GRO_CB(skb)->csum_cnt == 0 && > !NAPI_GRO_CB(skb)->csum_valid) || > !udp_sk(sk)->gro_receive) > goto out_unlock; > > I am trying to remember why this needs to check csum_cnt. If there was > a csum_cnt for the UDP csum being zero from checksum-unnecessary, it > was consumed by skb_gro_checksum_validate_zero_check in UDP4 GRO > received. We have met the scene about two VMs in different host with vxlan packets, when udp4_gro_receive receives one packet with ip_summed=CHECKSUM_NONE,csum_cnt=0,csum_valid=0,and udp->check=0, then skb_gro_checksum_validate_zero_check()-> skb_gro_incr_csum_unnecessary() validate it and set ip_summed=CHECKSUM_UNNECESSARY,csum_level=0, but csum_cnt and csum_valid keep zero value. Then it will be flushed in udp_gro_receive(), the codes as you have showed. so I think it forgets to modify csum_cnt since csum_level is changed in skb_gro_incr_csum_unnecessary()->__skb_incr_checksum_unnecessary(). > > . >