Re: [PATCH net v2] mctp i3c: fix MCTP I3C driver multi-thread issue

[Paolo Abeni]

On 1/7/25 4:15 AM, 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?

For the record, I'm taking the liberty of dropping the above paragraph
from the changelog, as the question IMHO should have been placed after
the --- separator, has been already replied and repost just for this
change would consume more time from everyone.

Cheers,

Paolo