netdev - Re: [PATCH net-next 1/2] tcp: TCP experimental option for SMC

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Date:   Mon, 16 Oct 2017 09:13:27 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Ursula Braun <ubraun@...ux.vnet.ibm.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        linux-s390@...r.kernel.org, jwi@...ux.vnet.ibm.com,
        schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
        raspl@...ux.vnet.ibm.com
Subject: Re: [PATCH net-next 1/2] tcp: TCP experimental option for SMC

On Mon, 2017-10-16 at 17:42 +0200, Ursula Braun wrote:
...

> +static void smc_set_capability(struct inet_request_sock *ireq,
> +			       const struct tcp_options_received *rx_opt)
> +{
> +#if IS_ENABLED(CONFIG_SMC)
> +	if (!static_key_false(&tcp_have_smc))
> +		return;
> +
> +	if (rx_opt->smc_ok)
> +		ireq->smc_ok = 1;
> +	else
> +		ireq->smc_ok = 0;
> +#endif
> +}


I do not think this static_key_false(&tcp_have_smc)) makes sense here.

1) If you have a SYN packet while the key is not set
2) Then tcp_have_smc is changed
3) ACK packets comes,  and finds random value in ireq->smc_ok

So really here you have to set this field.

static void smc_set_capability(struct inet_request_sock *ireq,
                              const struct tcp_options_received *rx_opt)
{
#if IS_ENABLED(CONFIG_SMC)
       ireq->smc_ok = rx_opt->smc_ok;
#endif
}