linux-kernel - Re: [PATCH v5 bpf-next 07/11] tcp: Migrate TCP_NEW_SYN_RECV requests at receiving the final ACK.

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Message-ID: <20210515011305.eeblnqnov4xlcjfy@kafai-mbp>
Date:   Fri, 14 May 2021 18:13:05 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Kuniyuki Iwashima <kuniyu@...zon.co.jp>
CC:     "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>,
        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 v5 bpf-next 07/11] tcp: Migrate TCP_NEW_SYN_RECV requests
 at receiving the final ACK.

On Mon, May 10, 2021 at 12:44:29PM +0900, Kuniyuki Iwashima wrote:
> diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> index e690d1cff36e..fe666dc5c621 100644
> --- a/net/ipv4/inet_connection_sock.c
> +++ b/net/ipv4/inet_connection_sock.c
> @@ -1075,10 +1075,38 @@ struct sock *inet_csk_complete_hashdance(struct sock *sk, struct sock *child,
>  	if (own_req) {
>  		inet_csk_reqsk_queue_drop(sk, req);
>  		reqsk_queue_removed(&inet_csk(sk)->icsk_accept_queue, req);
In the migration case 'sk != req->rsk_listener', is sk the right
one to pass in the above two functions?

> -		if (inet_csk_reqsk_queue_add(sk, req, child))
> +
> +		if (sk != req->rsk_listener) {
> +			/* another listening sk has been selected,
> +			 * migrate the req to it.
> +			 */
> +			struct request_sock *nreq;
> +
> +			/* hold a refcnt for the nreq->rsk_listener
> +			 * which is assigned in reqsk_clone()
> +			 */
> +			sock_hold(sk);
> +			nreq = reqsk_clone(req, sk);
> +			if (!nreq) {
> +				inet_child_forget(sk, req, child);
> +				goto child_put;
> +			}
> +
> +			refcount_set(&nreq->rsk_refcnt, 1);
> +			if (inet_csk_reqsk_queue_add(sk, nreq, child)) {
> +				reqsk_migrate_reset(req);
> +				reqsk_put(req);
> +				return child;
> +			}
> +
> +			reqsk_migrate_reset(nreq);
> +			__reqsk_free(nreq);
> +		} else if (inet_csk_reqsk_queue_add(sk, req, child)) {
>  			return child;
> +		}
>  	}
>  	/* Too bad, another child took ownership of the request, undo. */
> +child_put:
>  	bh_unlock_sock(child);
>  	sock_put(child);
>  	return NULL;