netdev - Re: [PATCH net v2] net/smc: avoid data corruption caused by decline

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Message-ID: <7fe3a213-3d2e-42d5-b44b-bbd761a01bba@linux.ibm.com>
Date: Fri, 17 Nov 2023 13:35:56 +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 v2] net/smc: avoid data corruption caused by decline



On 17.11.23 05:59, 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.
> 

Hi D.Wythe,

I think you understood me wrong. I mean we don't need sysctl. I like the 
first version more, where you just need to add some comments in the code.

Thanks,
Wenjia