netdev - Re: [PATCH net-next v5 2/5] net/smc: Limit backlog connections

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Date:   Wed, 9 Feb 2022 15:11:12 +0800
From:   "D. Wythe" <alibuda@...ux.alibaba.com>
To:     Karsten Graul <kgraul@...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-next v5 2/5] net/smc: Limit backlog connections


There are indirectly limits on smc accept queue with following code.

+	if (sk_acceptq_is_full(&smc->sk)) {
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
+		goto drop;
+	}


In fact, we treat the connections in smc accept queue as Full 
establisted connection. As I wrote in patch commits, there are 
trade-offs to this implemets.

Thanks.

在 2022/2/9 上午1:13, Karsten Graul 写道:
> On 08/02/2022 13:53, D. Wythe wrote:
>> From: "D. Wythe" <alibuda@...ux.alibaba.com>
>>
>> Current implementation does not handling backlog semantics, one
>> potential risk is that server will be flooded by infinite amount
>> connections, even if client was SMC-incapable.
> 
> In this patch you count the number of inflight SMC handshakes as pending and
> check them against the defined max_backlog. I really like this improvement.
> 
> There is another queue in af_smc.c, the smc accept queue and any new client
> socket that completed the handshake process is enqueued there (in smc_accept_enqueue() )
> and is waiting to get accepted by the user space application. To apply the correct
> semantics here, I think the number of sockets waiting in the smc accept queue
> should also be counted as backlog connections, right? I see no limit for this queue
> now. What do you think?