netdev - Re: [RFC PATCH bpf-next v5 2/2] net: Add additional bit to support clockid

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Message-ID: <6eb5b283-a9bd-4081-8bce-a60d72af430c@quicinc.com>
Date: Tue, 30 Apr 2024 12:16:35 -0700
From: "Abhishek Chauhan (ABC)" <quic_abchauha@...cinc.com>
To: Martin KaFai Lau <martin.lau@...ux.dev>,
        Willem de Bruijn
	<willemdebruijn.kernel@...il.com>
CC: "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni
	<pabeni@...hat.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Andrew Halaney <ahalaney@...hat.com>,
        "Martin
 KaFai Lau" <martin.lau@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, bpf <bpf@...r.kernel.org>,
        <kernel@...cinc.com>
Subject: Re: [RFC PATCH bpf-next v5 2/2] net: Add additional bit to support
 clockid_t timestamp type



On 4/26/2024 4:50 PM, Martin KaFai Lau wrote:
> On 4/26/24 11:46 AM, Abhishek Chauhan (ABC) wrote:
>>>> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
>>>> index 591226dcde26..f195b31d6e75 100644
>>>> --- a/net/ipv4/ip_output.c
>>>> +++ b/net/ipv4/ip_output.c
>>>> @@ -1457,7 +1457,7 @@ struct sk_buff *__ip_make_skb(struct sock *sk,
>>>>          skb->priority = (cork->tos != -1) ? cork->priority: READ_ONCE(sk->sk_priority);
>>>>        skb->mark = cork->mark;
>>>> -    skb->tstamp = cork->transmit_time;
>>>> +    skb_set_tstamp_type_frm_clkid(skb, cork->transmit_time, sk->sk_clockid);
>>> hmm... I think this will break for tcp. This sequence in particular:
>>>
>>> tcp_v4_timewait_ack()
>>>    tcp_v4_send_ack()
>>>      ip_send_unicast_reply()
>>>        ip_push_pending_frames()
>>>          ip_finish_skb()
>>>            __ip_make_skb()
>>>              /* sk_clockid is REAL but cork->transmit_time should be in mono */
>>>              skb_set_tstamp_type_frm_clkid(skb, cork->transmit_time, sk->sk_clockid);;
>>>
>>> I think I hit it from time to time when running the test in this patch set.
>>>
>> do you think i need to check for protocol type here . since tcp uses Mono and the rest according to the new design is based on
>> sk->sk_clockid
>> if (iph->protocol == IPPROTO_TCP)
>>     skb_set_tstamp_type_frm_clkid(skb, cork->transmit_time, CLOCK_MONOTONIC);
>> else
>>     skb_set_tstamp_type_frm_clkid(skb, cork->transmit_time, sk->sk_clockid);
> 
> Looks ok. iph->protocol is from sk->sk_protocol. I would defer to Willem input here.
> 
> There is at least one more place that needs this protocol check, __ip6_make_skb().

Sounds good. I will wait for Willem to comment here.