netdev - Re: [PATCH net] net/smc: fix unexpected SMC_CLC_DECL_ERR

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Message-ID: <cc0678b3-304c-0841-db15-ffb2117b63f6@linux.alibaba.com>
Date:   Wed, 2 Mar 2022 19:44:15 +0800
From:   "D. Wythe" <alibuda@...ux.alibaba.com>
To:     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] net/smc: fix unexpected SMC_CLC_DECL_ERR_REGRMB error



在 2022/3/1 下午9:17, D. Wythe 写道:
> From: "D. Wythe" <alibuda@...ux.alibaba.com>
> 
> Remove connections from link group is not synchronous with handling
> SMC_LLC_DELETE_RKEY, which means that even the number of connections is
> less that SMC_RMBS_PER_LGR_MAX, it does not mean that the connection can
> register rtoken successfully later, in other words, the rtoken entry may
> have not been released. This will cause an unexpected
> SMC_CLC_DECL_ERR_REGRMB to be reported, and then ths smc connection have
> to fallback to TCP.
> 
> We found that the main reason for the problem dues to following execution
> sequence:
> 
> Server Conn A:           Server Conn B:			Client Conn B:
> 
> smc_lgr_unregister_conn
>                          smc_lgr_register_conn
>                          smc_clc_send_accept     ->
>                                                          smc_rtoken_add
> smcr_buf_unuse
> 		->		Client Conn A:
> 				smc_rtoken_delete
> 
> smc_lgr_unregister_conn() makes current link available to assigned to new
> incoming connection, while smcr_buf_unuse() has not executed yet, which
> means that smc_rtoken_add may fail because of insufficient rtoken_entry,
> reversing their execution order will avoid this problem.
> 
> Fixes: 3e034725c0d8 ("net/smc: common functions for RMBs and send buffers")
> Signed-off-by: D. Wythe <alibuda@...ux.alibaba.com>
> ---
>   net/smc/smc_core.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
> index 2f321d2..c9c3a68 100644
> --- a/net/smc/smc_core.c
> +++ b/net/smc/smc_core.c
> @@ -1161,8 +1161,8 @@ void smc_conn_free(struct smc_connection *conn)
>   			cancel_work_sync(&conn->abort_work);
>   	}
>   	if (!list_empty(&lgr->list)) {
> -		smc_lgr_unregister_conn(conn);
>   		smc_buf_unuse(conn, lgr); /* allow buffer reuse */
> +		smc_lgr_unregister_conn(conn);
>   	}
>   
>   	if (!lgr->conns_num)

I have two patch for this issue, and i missed one, I'll post it in v2 
series.