Re: [RFC PATCH bpf-next v5 2/2] net: Add additional bit to support clockid_t timestamp type

[Martin KaFai Lau]

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().