netdev - Re: [PATCH net 3/5] net/smc: allow cdc msg send rather than drop it with NULL sndbuf

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Date: Wed, 11 Oct 2023 22:37:35 +0200
From: Wenjia Zhang <wenjia@...ux.ibm.com>
To: "D. Wythe" <alibuda@...ux.alibaba.com>, kgraul@...ux.ibm.com,
        jaka@...ux.ibm.com, wintera@...ux.ibm.com
Cc: kuba@...nel.org, davem@...emloft.net, netdev@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: Re: [PATCH net 3/5] net/smc: allow cdc msg send rather than drop it
 with NULL sndbuf_desc



On 11.10.23 09:33, D. Wythe wrote:
> From: "D. Wythe" <alibuda@...ux.alibaba.com>
> 
> This patch re-fix the issues memtianed by commit 22a825c541d7
> ("net/smc: fix NULL sndbuf_desc in smc_cdc_tx_handler()").
> 
> Blocking sending message do solve the issues though, but it also
> prevents the peer to receive the final message. Besides, in logic,
> whether the sndbuf_desc is NULL or not have no impact on the processing
> of cdc message sending.
> 
Agree.

> Hence that, this patch allow the cdc message sending but to check the
> sndbuf_desc with care in smc_cdc_tx_handler().
> 
> Fixes: 22a825c541d7 ("net/smc: fix NULL sndbuf_desc in smc_cdc_tx_handler()")
> Signed-off-by: D. Wythe <alibuda@...ux.alibaba.com>
> ---
>   net/smc/smc_cdc.c | 9 ++++-----
>   1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/net/smc/smc_cdc.c b/net/smc/smc_cdc.c
> index 01bdb79..3c06625 100644
> --- a/net/smc/smc_cdc.c
> +++ b/net/smc/smc_cdc.c
> @@ -28,13 +28,15 @@ static void smc_cdc_tx_handler(struct smc_wr_tx_pend_priv *pnd_snd,
>   {
>   	struct smc_cdc_tx_pend *cdcpend = (struct smc_cdc_tx_pend *)pnd_snd;
>   	struct smc_connection *conn = cdcpend->conn;
> +	struct smc_buf_desc *sndbuf_desc;
>   	struct smc_sock *smc;
>   	int diff;
>   
> +	sndbuf_desc = conn->sndbuf_desc;
>   	smc = container_of(conn, struct smc_sock, conn);
>   	bh_lock_sock(&smc->sk);
> -	if (!wc_status) {
> -		diff = smc_curs_diff(cdcpend->conn->sndbuf_desc->len,
> +	if (!wc_status && sndbuf_desc) {
> +		diff = smc_curs_diff(sndbuf_desc->len,
How could this guarantee that the sndbuf_desc would not be NULL?

>   				     &cdcpend->conn->tx_curs_fin,
>   				     &cdcpend->cursor);
>   		/* sndbuf_space is decreased in smc_sendmsg */
> @@ -114,9 +116,6 @@ int smc_cdc_msg_send(struct smc_connection *conn,
>   	union smc_host_cursor cfed;
>   	int rc;
>   
> -	if (unlikely(!READ_ONCE(conn->sndbuf_desc)))
> -		return -ENOBUFS;
> -
>   	smc_cdc_add_pending_send(conn, pend);
>   
>   	conn->tx_cdc_seq++;