netdev - Re: [PATCH] net/smc: loop in smc

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Date:   Mon, 22 Nov 2021 11:19:18 +0800
From:   Tony Lu <tonylu@...ux.alibaba.com>
To:     Daxing Guo <guodaxing@...wei.com>
Cc:     netdev@...r.kernel.org, chenzhe@...wei.com,
        linux-s390@...r.kernel.org, greg@...ah.com
Subject: Re: [PATCH] net/smc: loop in smc_listen

On Sat, Nov 20, 2021 at 03:54:51PM +0800, Daxing Guo wrote:
> From: Guo DaXing <guodaxing@...wei.com>
> 
> The kernel_listen function in smc_listen will fail when all the available
> ports are occupied.  At this point smc->clcsock->sk->sk_data_ready has 
> been changed to smc_clcsock_data_ready.  When we call smc_listen again, 
> now both smc->clcsock->sk->sk_data_ready and smc->clcsk_data_ready point 
> to the smc_clcsock_data_ready function.
> 
> The smc_clcsock_data_ready() function calls lsmc->clcsk_data_ready which 
> now points to itself resulting in an infinite loop.
> 
> This patch restores smc->clcsock->sk->sk_data_ready with the old value.

Hi Guo,

This indeed seems to be an issue. When listen fails, the original
clcsock's sk_data_ready overwrites by smc_clcsock_data_ready and can't
be recovered. I will also test it in my environment, thanks.

Cheers,
Tony Lu

> 
> Signed-off-by: Guo DaXing <guodaxing@...wei.com>
> ---
>  net/smc/af_smc.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
> index 59284da9116d..078f5edf6d4d 100644
> --- a/net/smc/af_smc.c
> +++ b/net/smc/af_smc.c
> @@ -2120,8 +2120,10 @@ static int smc_listen(struct socket *sock, int backlog)
>  	smc->clcsock->sk->sk_user_data =
>  		(void *)((uintptr_t)smc | SK_USER_DATA_NOCOPY);
>  	rc = kernel_listen(smc->clcsock, backlog);
> -	if (rc)
> +	if (rc) {
> +		smc->clcsock->sk->sk_data_ready = smc->clcsk_data_ready;
>  		goto out;
> +	}
>  	sk->sk_max_ack_backlog = backlog;
>  	sk->sk_ack_backlog = 0;
>  	sk->sk_state = SMC_LISTEN;
> -- 
> 2.20.1