netdev - Re: [PATCH v12 net-next 12/15] tcp: accecn: AccECN option send control

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Message-ID: <e3bef5ed-535f-4ce3-9ea4-f6a40df448ff@redhat.com>
Date: Mon, 14 Jul 2025 17:12:20 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: chia-yu.chang@...ia-bell-labs.com, edumazet@...gle.com,
 linux-doc@...r.kernel.org, corbet@....net, horms@...nel.org,
 dsahern@...nel.org, kuniyu@...zon.com, bpf@...r.kernel.org,
 netdev@...r.kernel.org, dave.taht@...il.com, jhs@...atatu.com,
 kuba@...nel.org, stephen@...workplumber.org, xiyou.wangcong@...il.com,
 jiri@...nulli.us, davem@...emloft.net, andrew+netdev@...n.ch,
 donald.hunter@...il.com, ast@...erby.net, liuhangbin@...il.com,
 shuah@...nel.org, linux-kselftest@...r.kernel.org, ij@...nel.org,
 ncardwell@...gle.com, koen.de_schepper@...ia-bell-labs.com,
 g.white@...lelabs.com, ingemar.s.johansson@...csson.com,
 mirja.kuehlewind@...csson.com, cheshire@...le.com, rs.ietf@....at,
 Jason_Livingood@...cast.com, vidhi_goel@...le.com
Subject: Re: [PATCH v12 net-next 12/15] tcp: accecn: AccECN option send
 control

On 7/4/25 10:53 AM, chia-yu.chang@...ia-bell-labs.com wrote:
> @@ -1151,7 +1155,10 @@ static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb
>  	}
>  
>  	if (tcp_ecn_mode_accecn(tp) &&
> -	    READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option)) {
> +	    READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option) &&
> +	    (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option) >= TCP_ACCECN_OPTION_FULL ||
> +	     tp->accecn_opt_demand ||
> +	     tcp_accecn_option_beacon_check(sk))) {
>  		opts->use_synack_ecn_bytes = 0;
>  		size += tcp_options_fit_accecn(opts, tp->accecn_minlen,
>  					       MAX_TCP_OPTION_SPACE - size);

whoops, I almost missed it...

Please call READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option) only
once, i.e.:

	if (tcp_ecn_mode_accecn(tp)) {
		int ecn_opt = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option);

		if (ecn_opt && (ecn_opt >= TCP_ACCECN_OPTION_FULL || // ...

/P