netdev - Re: [PATCH net v1] net/smc: avoid data corruption caused by decline

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Message-ID: <05c29431-c941-45d1-8e14-0527accc3993@linux.ibm.com>
Date: Wed, 8 Nov 2023 14:00:58 +0100
From: Wenjia Zhang <wenjia@...ux.ibm.com>
To: "D. Wythe" <alibuda@...ux.alibaba.com>, kgraul@...ux.ibm.com,
        jaka@...ux.ibm.com, wintera@...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 v1] net/smc: avoid data corruption caused by decline



On 08.11.23 10:48, D. Wythe wrote:
> From: "D. Wythe" <alibuda@...ux.alibaba.com>
> 
> We found a data corruption issue during testing of SMC-R on Redis
> applications.
> 
> The benchmark has a low probability of reporting a strange error as
> shown below.
> 
> "Error: Protocol error, got "\xe2" as reply type byte"
> 
> Finally, we found that the retrieved error data was as follows:
> 
> 0xE2 0xD4 0xC3 0xD9 0x04 0x00 0x2C 0x20 0xA6 0x56 0x00 0x16 0x3E 0x0C
> 0xCB 0x04 0x02 0x01 0x00 0x00 0x20 0x00 0x00 0x00 0x00 0x00 0x00 0x00
> 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0xE2
> 
> It is quite obvious that this is a SMC DECLINE message, which means that
> the applications received SMC protocol message.
> We found that this was caused by the following situations:
> 
> client			server
> 	   proposal
> 	------------->
> 	   accept
> 	<-------------
> 	   confirm
> 	------------->
> wait confirm
> 
> 	 failed llc confirm
> 	    x------
> (after 2s)timeout
> 			wait rsp
> 
> wait decline
> 
> (after 1s) timeout
> 			(after 2s) timeout
> 	    decline
> 	-------------->
> 	    decline
> 	<--------------
> 
> As a result, a decline message was sent in the implementation, and this
> message was read from TCP by the already-fallback connection.
> 
> This patch double the client timeout as 2x of the server value,
> With this simple change, the Decline messages should never cross or
> collide (during Confirm link timeout).
> 
> This issue requires an immediate solution, since the protocol updates
> involve a more long-term solution.
> 
> Fixes: 0fb0b02bd6fd ("net/smc: adapt SMC client code to use the LLC flow")
> Signed-off-by: D. Wythe <alibuda@...ux.alibaba.com>
> ---
>   net/smc/af_smc.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
> index abd2667..5b91f55 100644
> --- a/net/smc/af_smc.c
> +++ b/net/smc/af_smc.c
> @@ -599,7 +599,7 @@ static int smcr_clnt_conf_first_link(struct smc_sock *smc)
>   	int rc;
>   
>   	/* receive CONFIRM LINK request from server over RoCE fabric */
> -	qentry = smc_llc_wait(link->lgr, NULL, SMC_LLC_WAIT_TIME,
> +	qentry = smc_llc_wait(link->lgr, NULL, 2 * SMC_LLC_WAIT_TIME,
>   			      SMC_LLC_CONFIRM_LINK);
>   	if (!qentry) {
>   		struct smc_clc_msg_decline dclc;
I'm wondering if the double time (if sufficient) of timeout could be for 
waiting for CLC_DECLINE on the client's side. i.e.

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index 35ddebae8894..9b1feef1013d 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -605,7 +605,7 @@ static int smcr_clnt_conf_first_link(struct smc_sock 
*smc)
                 struct smc_clc_msg_decline dclc;

                 rc = smc_clc_wait_msg(smc, &dclc, sizeof(dclc),
-                                     SMC_CLC_DECLINE, CLC_WAIT_TIME_SHORT);
+                                     SMC_CLC_DECLINE, 2 * 
CLC_WAIT_TIME_SHORT);
                 return rc == -EAGAIN ? SMC_CLC_DECL_TIMEOUT_CL : rc;
         }
         smc_llc_save_peer_uid(qentry);

Because the purpose is to let the server have the control to deline.