netdev - Re: [PATCH v3 net] ipv6: tcp: drop silly ICMPv6 packet too big messages

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Message-ID: <20220315161907.653379f8@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Tue, 15 Mar 2022 16:19:07 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Maciej Żenczykowski <maze@...gle.com>,
        Martin KaFai Lau <kafai@...com>, ntspring@...com
Subject: Re: [PATCH v3 net] ipv6: tcp: drop silly ICMPv6 packet too big
 messages

On Thu,  8 Jul 2021 00:21:09 -0700 Eric Dumazet wrote:
> +	/* Drop requests trying to increase our current mss.
> +	 * Check done in __ip6_rt_update_pmtu() is too late.
> +	 */
> +	if (tcp_mtu_to_mss(sk, mtu) >= tcp_sk(sk)->mss_cache)
> +		return;

Hi Eric! I think this breaks TFO + pMTU.

mss_cache is 1208 but TFO seems to use tp->rx_opt.mss_clamp
to size the packet. So we ignore the incoming PTB. Should we 
init mss_cache for TFO?