netdev - Re: [PATCH net-next] udp: Fix kernel panic in UDP GSO path

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Message-ID: <CAF=yD-LgpWrrhXuySMsF2sgJ9EUNZbQjQw2SQsLasF9Q1LG4aA@mail.gmail.com>
Date:   Mon, 14 May 2018 19:07:37 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Sean Tranchetti <stranche@...eaurora.org>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Willem de Bruijn <willemb@...gle.com>,
        David Miller <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>
Subject: Re: [PATCH net-next] udp: Fix kernel panic in UDP GSO path

>> Paged skbuffs is an optimization for gso, but the feature should
>> continue to work even if gso skbs are linear, indeed (if at the cost
>> of copying during skb_segment).
>>
>> We need to make paged contingent on scatter-gather. Rough
>> patch below. That is for ipv4 only, the same will be needed for ipv6.
>>
>> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
>> index b5e21eb198d8..b38731d8a44f 100644
>> --- a/net/ipv4/ip_output.c
>> +++ b/net/ipv4/ip_output.c
>> @@ -884,7 +884,7 @@ static int __ip_append_data(struct sock *sk,
>>
>>         exthdrlen = !skb ? rt->dst.header_len : 0;
>>         mtu = cork->gso_size ? IP_MAX_MTU : cork->fragsize;
>> -       paged = !!cork->gso_size;
>> +       paged = cork->gso_size && (rt->dst.dev->features & NETIF_F_SG);
>
>
> Hi Willem. That's definitely a much cleaner patch than ours since it allows
> the GSO to continue without failure.
> We tried it on both the IPv4 and IPv6 path and didn't see the crash in
> either case.

Thanks for testing. I have a small set of fixes to udp gso, including
this one. Let me send them right away.