netdev - Re: [PATCH net] mctp i3c: fix MCTP I3C driver multi-thread issue

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Message-ID: <20250102180845.30742771@kernel.org>
Date: Thu, 2 Jan 2025 18:08:45 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Leo Yang <leo.yang.sy0@...il.com>
Cc: jk@...econstruct.com.au, matt@...econstruct.com.au,
 andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com,
 pabeni@...hat.com, netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 Leo Yang <Leo-Yang@...ntatw.com>
Subject: Re: [PATCH net] mctp i3c: fix MCTP I3C driver multi-thread issue

On Thu, 26 Dec 2024 10:53:19 +0800 Leo Yang wrote:
> We found a timeout problem with the pldm command on our system.  The
> reason is that the MCTP-I3C driver has a race condition when receiving
> multiple-packet messages in multi-thread, resulting in a wrong packet
> order problem.
> 
> We identified this problem by adding a debug message to the
> mctp_i3c_read function.
> 
> According to the MCTP spec, a multiple-packet message must be composed
> in sequence, and if there is a wrong sequence, the whole message will be
> discarded and wait for the next SOM.
> For example, SOM → Pkt Seq #2 → Pkt Seq #1 → Pkt Seq #3 → EOM.
> 
> Therefore, we try to solve this problem by adding a mutex to the
> mctp_i3c_read function.  Before the modification, when a command
> requesting a multiple-packet message response is sent consecutively, an
> error usually occurs within 100 loops.  After the mutex, it can go
> through 40000 loops without any error, and it seems to run well.
> 
> But I'm a little worried about the performance of mutex in high load
> situation (as spec seems to allow different endpoints to respond at the
> same time), do you think this is a feasible solution?

I don't see any obvious problem, Tx seems to hold this lock already.
Could you repost with a Fixes tag added?
-- 
pw-bot: cr