netdev - Re: [PATCH net-next 2/4] tcp_metrics: properly set tp->snd_ssthresh in tcp_init

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Date: Sat, 23 Sep 2023 13:08:57 +0200
From: David Ahern <dsahern@...nel.org>
To: Eric Dumazet <edumazet@...gle.com>, "David S . Miller"
 <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>
Cc: Neal Cardwell <ncardwell@...gle.com>, Yuchung Cheng <ycheng@...gle.com>,
 netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net-next 2/4] tcp_metrics: properly set tp->snd_ssthresh
 in tcp_init_metrics()

On 9/22/23 4:03 PM, Eric Dumazet wrote:
> We need to set tp->snd_ssthresh to TCP_INFINITE_SSTHRESH
> in the case tcp_get_metrics() fails for some reason.
> 
> Fixes: 9ad7c049f0f7 ("tcp: RFC2988bis + taking RTT sample from 3WHS for the passive open side")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> ---
>  net/ipv4/tcp_metrics.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/net/ipv4/tcp_metrics.c b/net/ipv4/tcp_metrics.c
> index 4bfa2fb27de5481ca3d1300d7e7b2c80d1577a31..0c03f564878ff0a0dbefd9b631f54697346c8fa9 100644
> --- a/net/ipv4/tcp_metrics.c
> +++ b/net/ipv4/tcp_metrics.c
> @@ -470,6 +470,10 @@ void tcp_init_metrics(struct sock *sk)
>  	u32 val, crtt = 0; /* cached RTT scaled by 8 */
>  
>  	sk_dst_confirm(sk);
> +	/* ssthresh may have been reduced unnecessarily during.
> +	 * 3WHS. Restore it back to its initial default.
> +	 */
> +	tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;

This would read easier with newlines after sk_dst_confirm and again here.
>  	if (!dst)
>  		goto reset;
>  
> @@ -489,11 +493,6 @@ void tcp_init_metrics(struct sock *sk)
>  		tp->snd_ssthresh = val;
>  		if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
>  			tp->snd_ssthresh = tp->snd_cwnd_clamp;
> -	} else {
> -		/* ssthresh may have been reduced unnecessarily during.
> -		 * 3WHS. Restore it back to its initial default.
> -		 */
> -		tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
>  	}
>  	val = tcp_metric_get(tm, TCP_METRIC_REORDERING);
>  	if (val && tp->reordering != val)

Reviewed-by: David Ahern <dsahern@...nel.org>