netdev - Re: [PATCH][net-next] net: slightly optimize eth_type

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Message-Id: <20181117.165138.801331179496411533.davem@davemloft.net>
Date:   Sat, 17 Nov 2018 16:51:38 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     eric.dumazet@...il.com
Cc:     lirongqing@...du.com, netdev@...r.kernel.org
Subject: Re: [PATCH][net-next] net: slightly optimize eth_type_trans

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Sat, 17 Nov 2018 14:37:12 -0800

> 
> 
> On 11/15/2018 03:11 PM, David Miller wrote:
> 
>> 
>> Applied.
>> 
> 
> While reviewing this stuff, I found we have a bug.
> 
> If napi_reuse_skb() is called, we might inherit from prior skb->pkt_type value.
> 
> It seems that GRO could aggregate packets with pkt_type != PACKET_HOST, right ?
> 
> David, any objection if I submit the following fix ?

Oh weird, so we do GRO frags accumulation using SKB which never goes through
eth_type_trans()?

I don't understand how we can, in this circumstance, assume PACKET_HOST?

Because that is what your suggested patch does.

Frame could be UDP multicast, and we could legitimately GRO accumulate it.
In that situations setting PACKET_HOST doesn't seem correct.