netdev - IP ID check (flush_id) in inet_gro_receive is necessary or not？

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Message-ID: <5771FFA1.3050306@huawei.com>
Date:	Tue, 28 Jun 2016 12:40:01 +0800
From:	Tan Xiaojun <tanxiaojun@...wei.com>
To:	<davem@...emloft.net>, <kuznet@....inr.ac.ru>, <jmorris@...ei.org>,
	<yoshfuji@...ux-ipv6.org>, <kaber@...sh.net>,
	<aduyck@...antis.com>, <hkchu@...gle.com>
CC:	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: IP ID check (flush_id) in inet_gro_receive is necessary or not？

Hi everyone,

	I'm sorry to bother you. But I was confused.

	The IP ID check (flush_id) in inet_gro_receive is only used by tcp_gro_receive, and in tcp_gro_receive we have tcphdr check to ensure the order of skbs,
	like below:

	flush |= (__force int)(th->ack_seq ^ th2->ack_seq);
	flush |= (ntohl(th2->seq) + skb_gro_len(p)) ^ ntohl(th->seq);

	So if I remove the IP ID check in inet_gro_receive, there will be a problem ? And under what circumstances ?


Thanks.
Xiaojun.