Subject: Re: [RFC PATCH bpf-next v6 2/3] net: Add additional bit to support clockid_t timestamp type

From: Martin KaFai Lau <[email-masked]>
Date: Mon, 6 May 2024 17:44:56 -0700

On 5/3/24 8:13 PM, Abhishek Chauhan wrote:
> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
> index fe86cadfa85b..c3d852eecb01 100644
> --- a/net/ipv4/ip_output.c
> +++ b/net/ipv4/ip_output.c
> @@ -1457,7 +1457,10 @@ 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;
> +	if (sk_is_tcp(sk))

This seems not catching all IPPROTO_TCP case. In particular, the percpu 
"ipv4_tcp_sk" is SOCK_RAW. sk_is_tcp() is checking SOCK_STREAM:

void __init tcp_v4_init(void)
{

	/* ... */
	res = inet_ctl_sock_create(&sk, PF_INET, SOCK_RAW,
				   IPPROTO_TCP, &init_net);

	/* ... */
}

"while :; do ./test_progs -t tc_redirect/tc_redirect_dtime || break; done" 
failed pretty often exactly in this case.

> +		skb_set_delivery_type_by_clockid(skb, cork->transmit_time, CLOCK_MONOTONIC);
> +	else
> +		skb_set_delivery_type_by_clockid(skb, cork->transmit_time, sk->sk_clockid);
>   	/*
>   	 * Steal rt from cork.dst to avoid a pair of atomic_inc/atomic_dec
>   	 * on dst refcount

[ ... ]

> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index 05067bd44775..797a9764e8fe 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -1924,7 +1924,10 @@ struct sk_buff *__ip6_make_skb(struct sock *sk,
>   
>   	skb->priority = READ_ONCE(sk->sk_priority);
>   	skb->mark = cork->base.mark;
> -	skb->tstamp = cork->base.transmit_time;
> +	if (sk_is_tcp(sk))
> +		skb_set_delivery_type_by_clockid(skb, cork->base.transmit_time, CLOCK_MONOTONIC);
> +	else
> +		skb_set_delivery_type_by_clockid(skb, cork->base.transmit_time, sk->sk_clockid);
>   
>   	ip6_cork_steal_dst(skb, cork);
>   	IP6_INC_STATS(net, rt->rt6i_idev, IPSTATS_MIB_OUTREQUESTS);