linux-kernel - Re: [PATCH v7 bpf-next 06/11] tcp: Migrate TCP_NEW_SYN_RECV requests at retransmitting SYN+ACKs.

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Date:   Thu, 10 Jun 2021 22:21:00 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Kuniyuki Iwashima <kuniyu@...zon.co.jp>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>
Cc:     Benjamin Herrenschmidt <benh@...zon.com>,
        Kuniyuki Iwashima <kuni1840@...il.com>, bpf@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 bpf-next 06/11] tcp: Migrate TCP_NEW_SYN_RECV requests
 at retransmitting SYN+ACKs.



On 5/21/21 8:20 PM, Kuniyuki Iwashima wrote:
> As with the preceding patch, this patch changes reqsk_timer_handler() to
> call reuseport_migrate_sock() and inet_reqsk_clone() to migrate in-flight
> requests at retransmitting SYN+ACKs. If we can select a new listener and
> clone the request, we resume setting the SYN+ACK timer for the new req. If
> we can set the timer, we call inet_ehash_insert() to unhash the old req and
> put the new req into ehash.
> 

...

>  static void reqsk_migrate_reset(struct request_sock *req)
>  {
> +	req->saved_syn = NULL;
> +	inet_rsk(req)->ireq_opt = NULL;
>  #if IS_ENABLED(CONFIG_IPV6)
> -	inet_rsk(req)->ipv6_opt = NULL;
> +	inet_rsk(req)->pktopts = NULL;
>  #endif
>  }

This is fragile. 

Maybe instead :

#if IS_ENABLED(CONFIG_IPV6)
	inet_rsk(req)->ipv6_opt = NULL;
	inet_rsk(req)->pktopts = NULL;
#else
	inet_rsk(req)->ireq_opt = NULL;
#endif