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

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Message-Id: <1646140644-121649-1-git-send-email-alibuda@linux.alibaba.com>
Date:   Tue,  1 Mar 2022 21:17:24 +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: [PATCH net] net/smc: fix unexpected SMC_CLC_DECL_ERR_REGRMB error

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)
-- 
1.8.3.1