netdev - Re: [PATCH net v4] net/smc: avoid data corruption caused by decline

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Date: Wed, 22 Nov 2023 09:54:20 +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, guwen@...ux.alibaba.com
Cc: kuba@...nel.org, davem@...emloft.net, netdev@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-rdma@...r.kernel.org,
        tonylu@...ux.alibaba.com, pabeni@...hat.com, edumazet@...gle.com
Subject: Re: [PATCH net v4] net/smc: avoid data corruption caused by decline



On 22.11.23 03:37, 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
>          ¦  clc proposal
>          ------------->
>          ¦  clc accept
>          <-------------
>          ¦  clc confirm
>          ------------->
> wait llc confirm
> 			send llc confirm
>          ¦failed llc confirm
>          ¦   x------
> (after 2s)timeout
>                          wait llc confirm 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>
> ---

Looks good to me! Thank you, D.Wythe!
Reviewed-by: Wenjia Zhang <wenjia@...ux.ibm.com>