linux-kernel - Re: [PATCH net] net/smc: Send out the remaining data in sndbuf before close

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Date:   Mon, 28 Mar 2022 17:04:11 +0800
From:   "dust.li" <dust.li@...ux.alibaba.com>
To:     Wen Gu <guwen@...ux.alibaba.com>, kgraul@...ux.ibm.com,
        davem@...emloft.net, kuba@...nel.org
Cc:     linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net/smc: Send out the remaining data in sndbuf
 before close

On Mon, Mar 28, 2022 at 02:10:36PM +0800, Wen Gu wrote:
>The current autocork algorithms will delay the data transmission
>in BH context to smc_release_cb() when sock_lock is hold by user.
>
>So there is a possibility that when connection is being actively
>closed (sock_lock is hold by user now), some corked data still
>remains in sndbuf, waiting to be sent by smc_release_cb(). This
>will cause:
>
>- smc_close_stream_wait(), which is called under the sock_lock,
>  has a high probability of timeout because data transmission is
>  delayed until sock_lock is released.
>
>- Unexpected data sends may happen after connction closed and use
>  the rtoken which has been deleted by remote peer through
>  LLC_DELETE_RKEY messages.
>
>So this patch will try to send out the remaining corked data in
>sndbuf before active close process, to ensure data integrity and
>avoid unexpected data transmission after close.

I think this issue should also happen if TCP_CORK is set and
autocorking is not enabled ?

Autocorking and delaying the TX from BH to smc_release_cb() greatly
increased the probability of this problem.

>
>Reported-by: Guangguan Wang <guangguan.wang@...ux.alibaba.com>
>Fixes: 6b88af839d20 ("net/smc: don't send in the BH context if sock_owned_by_user")
>Signed-off-by: Wen Gu <guwen@...ux.alibaba.com>
>---
> net/smc/smc_close.c | 3 +++
> 1 file changed, 3 insertions(+)
>
>diff --git a/net/smc/smc_close.c b/net/smc/smc_close.c
>index 292e4d9..676cb23 100644
>--- a/net/smc/smc_close.c
>+++ b/net/smc/smc_close.c
>@@ -57,6 +57,9 @@ static void smc_close_stream_wait(struct smc_sock *smc, long timeout)
> 	if (!smc_tx_prepared_sends(&smc->conn))
> 		return;
> 
>+	/* Send out corked data remaining in sndbuf */
>+	smc_tx_pending(&smc->conn);
>+
> 	smc->wait_close_tx_prepared = 1;
> 	add_wait_queue(sk_sleep(sk), &wait);
> 	while (!signal_pending(current) && timeout) {
>-- 
>1.8.3.1