netdev - Re: [PATCH net-next v1 3/9] net: devmem: preserve sockc

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Message-ID: <aCtMgDGQBbs0KkxZ@mini-arch>
Date: Mon, 19 May 2025 08:21:36 -0700
From: Stanislav Fomichev <stfomichev@...il.com>
To: Mina Almasry <almasrymina@...gle.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	Ilias Apalodimas <ilias.apalodimas@...aro.org>,
	Neal Cardwell <ncardwell@...gle.com>,
	Kuniyuki Iwashima <kuniyu@...zon.com>,
	David Ahern <dsahern@...nel.org>,
	Andrew Lunn <andrew+netdev@...n.ch>, Shuah Khan <shuah@...nel.org>,
	sdf@...ichev.me, ap420073@...il.com, praan@...gle.com,
	shivajikant@...gle.com
Subject: Re: [PATCH net-next v1 3/9] net: devmem: preserve sockc_err

On 05/19, Mina Almasry wrote:
> Preserve the error code returned by sock_cmsg_send and return that on
> err.
> 
> Signed-off-by: Mina Almasry <almasrymina@...gle.com>
> ---
>  net/ipv4/tcp.c | 24 ++++++++++--------------
>  1 file changed, 10 insertions(+), 14 deletions(-)
> 
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index b7b6ab41b496..45abe5772157 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -1067,7 +1067,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
>  	int flags, err, copied = 0;
>  	int mss_now = 0, size_goal, copied_syn = 0;
>  	int process_backlog = 0;
> -	bool sockc_valid = true;
> +	int sockc_err = 0;
>  	int zc = 0;
>  	long timeo;
>  
> @@ -1075,13 +1075,10 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
>  
>  	sockc = (struct sockcm_cookie){ .tsflags = READ_ONCE(sk->sk_tsflags) };
>  	if (msg->msg_controllen) {
> -		err = sock_cmsg_send(sk, msg, &sockc);
> -		if (unlikely(err))
> -			/* Don't return error until MSG_FASTOPEN has been
> -			 * processed; that may succeed even if the cmsg is
> -			 * invalid.
> -			 */
> -			sockc_valid = false;
> +		sockc_err = sock_cmsg_send(sk, msg, &sockc);
> +		/* Don't return error until MSG_FASTOPEN has been processed;
> +		 * that may succeed even if the cmsg is invalid.
> +		 */
>  	}
>  
>  	if ((flags & MSG_ZEROCOPY) && size) {
> @@ -1092,7 +1089,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
>  		} else if (sock_flag(sk, SOCK_ZEROCOPY)) {
>  			skb = tcp_write_queue_tail(sk);
>  			uarg = msg_zerocopy_realloc(sk, size, skb_zcopy(skb),
> -						    sockc_valid && !!sockc.dmabuf_id);
> +						    !sockc_err && !!sockc.dmabuf_id);

Why have these extra !! here? Other places below simply do '&& sockc.dmabuf_id',
why not the same here? 

>  			if (!uarg) {
>  				err = -ENOBUFS;
>  				goto out_err;
> @@ -1102,7 +1099,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
>  			else
>  				uarg_to_msgzc(uarg)->zerocopy = 0;
>  
> -			if (sockc_valid && sockc.dmabuf_id) {
> +			if (!sockc_err && sockc.dmabuf_id) {
>  				binding = net_devmem_get_binding(sk, sockc.dmabuf_id);
>  				if (IS_ERR(binding)) {
>  					err = PTR_ERR(binding);
> @@ -1116,7 +1113,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
>  			zc = MSG_SPLICE_PAGES;
>  	}
>  
> -	if (sockc_valid && sockc.dmabuf_id &&
> +	if (!sockc_err && sockc.dmabuf_id &&
>  	    (!(flags & MSG_ZEROCOPY) || !sock_flag(sk, SOCK_ZEROCOPY))) {
>  		err = -EINVAL;
>  		goto out_err;
> @@ -1160,9 +1157,8 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
>  		/* 'common' sending to sendq */
>  	}
>  
> -	if (!sockc_valid) {
> -		if (!err)
> -			err = -EINVAL;
> +	if (!!sockc_err) {

Same here, I don't think we need these extra !! ?