netdev - Re: [PATCH net-next 2/2] net/tcp: optimise io

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Message-ID: <99faed2d-8ea6-fc85-7f21-e15b24d041f1@kernel.org>
Date: Mon, 15 May 2023 11:29:56 -0600
From: David Ahern <dsahern@...nel.org>
To: Pavel Begunkov <asml.silence@...il.com>, io-uring@...r.kernel.org,
 netdev@...r.kernel.org, edumazet@...gle.com, davem@...emloft.net,
 kuba@...nel.org, pabeni@...hat.com
Subject: Re: [PATCH net-next 2/2] net/tcp: optimise io_uring zc ubuf
 refcounting

On 5/15/23 10:06 AM, Pavel Begunkov wrote:
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 40f591f7fce1..3d18e295bb2f 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -1231,7 +1231,6 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
>  	if ((flags & MSG_ZEROCOPY) && size) {
>  		if (msg->msg_ubuf) {
>  			uarg = msg->msg_ubuf;
> -			net_zcopy_get(uarg);
>  			zc = sk->sk_route_caps & NETIF_F_SG;
>  		} else if (sock_flag(sk, SOCK_ZEROCOPY)) {
>  			skb = tcp_write_queue_tail(sk);
> @@ -1458,7 +1457,9 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
>  		tcp_push(sk, flags, mss_now, tp->nonagle, size_goal);
>  	}
>  out_nopush:
> -	net_zcopy_put(uarg);
> +	/* msg->msg_ubuf is pinned by the caller so we don't take extra refs */
> +	if (uarg && !msg->msg_ubuf)
> +		net_zcopy_put(uarg);
>  	return copied + copied_syn;
>  
>  do_error:
> @@ -1467,7 +1468,9 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
>  	if (copied + copied_syn)
>  		goto out;
>  out_err:
> -	net_zcopy_put_abort(uarg, true);
> +	/* msg->msg_ubuf is pinned by the caller so we don't take extra refs */
> +	if (uarg && !msg->msg_ubuf)
> +		net_zcopy_put_abort(uarg, true);
>  	err = sk_stream_error(sk, flags, err);
>  	/* make sure we wake any epoll edge trigger waiter */
>  	if (unlikely(tcp_rtx_and_write_queues_empty(sk) && err == -EAGAIN)) {

Both net_zcopy_put_abort and net_zcopy_put have an `if (uarg)` check.