Re: [PATCH mptcp-next v4] mptcp: honour configured min/max RTO in retransmit paths

Hi Matt,

Thank you for the review!

> I guess we can remove these two lines because it was about fixes related
> to the route checks that are no longer used, and this might be confusing
> for others, right?

Yes, please drop both lines when applying.

> Also, usually there is no Reported-by tags when addressing review
> comments: (...)

Understood, I will make sure to follow this next time.

And thanks again to Li for the reviews on the earlier versions.

Cheers,
Kalpan Jani


From: Matthieu Baerts (NGI0) <[email protected]>
To: "Kalpan Jani"<[email protected]>
Cc: <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, "Li Xiasong"<[email protected]>
Date: Wed, 05 Aug 2026 14:56:42 +0530
Subject: Re: [PATCH mptcp-next v4] mptcp: honour configured min/max RTO in retransmit paths

 > Hi Kalpan,
 > 
 > > The MPTCP-level retransmit timers (DATA_FIN retransmissions and the
 > > fallback timeout) used the hard-coded TCP_RTO_MIN / TCP_RTO_MAX
 > > constants, ignoring the tcp_rto_min_us and tcp_rto_max_ms sysctls.
 > >
 > > Make them follow the sysctls instead: seed icsk_rto_min / icsk_rto_max
 > > on the MPTCP socket from the per-netns sysctls in __mptcp_init_sock()
 > > -- the msk does not go through tcp_init_sock(), so these fields would
 > > otherwise stay zero -- and read them directly where the constants were
 > > used:
 > >
 > > - mptcp_set_datafin_timeout(): both the backoff cap computation and
 > >   the resulting timer_ival. The two sysctls are validated
 > >   independently, so rto_min > rto_max is a valid configuration; keep
 > >   a max_t() guard so ilog2() is never called with 0.
 > >
 > > - __mptcp_set_timeout(): the fallback when no subflow timeout is
 > >   available.
 > >
 > > The icsk fields are read directly instead of using the
 > > tcp_rto_min()/tcp_rto_max() helpers: the MPTCP socket does not perform
 > > routing lookups in these paths, so the rto_min route metric checked by
 > > tcp_rto_min() can never apply here. The TCP_RTO_MIN_US /
 > > TCP_RTO_MAX_MS socket options are not supported by MPTCP setsockopt()
 > > either; this can be revisited if they get supported on MPTCP sockets.
 > >
 > > The remaining uses of TCP_RTO_MAX in net/mptcp/ctrl.c (default
 > > add_addr_timeout) and net/mptcp/subflow.c (MP_FAIL timeout) are
 > > intentionally left unchanged: they use the constant as a default
 > > duration, not as an RTO bound on a retransmit timer.
 > >
 > > Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/618
 > > Reported-by: Li Xiasong <[email protected]>
 > > Closes: https://lore.kernel.org/all/[email protected]/
 > 
 > I guess we can remove these two lines because it was about fixes related
 > to the route checks that are no longer used, and this might be confusing
 > for others, right?
 > 
 > If yes, no need to send a new version, I can remove them when applying
 > the patch. The rest looks good to me:
 > 
 > Reviewed-by: Matthieu Baerts (NGI0) <[email protected]>
 > 
 > Also, usually there is no Reported-by tags when addressing review
 > comments: you can either use 'Suggested-by' when the whole idea was
 > given by someone else, mention a person in the commit message if a part
 > of the idea is coming from someone else, or only in the changelog.
 > 
 > BTW, thank you, Li, for the previous review!
 > 
 > -- 
 > Matthieu Baerts (NGI0) <[email protected]>
 >