Re: [PATCH v5 mptcp-next 00/10] mptcp: introduce backlog processing

[Geliang Tang <geliang@kernel.org>]

Hi Paolo,

On Fri, 2025-10-10 at 10:21 +0200, Paolo Abeni wrote:
> On 10/9/25 3:58 PM, Paolo Abeni wrote:
> > @Geliang: if you reproduce the issue multiple times, are there any
> > common patterns ? i.e. sender files considerably larger than the
> > client
> > one, or only a specific subsets of all the test-cases failing, or
> > ...
> 
> Other questions:
> - Can you please share your setup details (VM vs baremetal, debug
> config
> vs non debug, vmg vs plain qemu, number of [v]cores...)? I can't
> repro
> the issue locally.

Here are my modifications:

https://git.kernel.org/pub/scm/linux/kernel/git/geliang/mptcp_net-next.git/log/?h=splice_new

I used mptcp-upstream-virtme-docker normal config to reproduce it:

docker run \
	-e INPUT_NO_BLOCK=1 \
	-e INPUT_PACKETDRILL_NO_SYNC=1 \
	-v "${PWD}:${PWD}:rw" -w "${PWD}" --privileged --rm -it \
        --pull always ghcr.io/multipath-tcp/mptcp-upstream-virtme-
docker:latest \
	auto-normal

$ cat .virtme-exec-run 
run_loop run_selftest_one ./mptcp_connect_splice.sh

Running mptcp_connect_splice.sh in a loop dozens of times should
reproduce the test failure.

> - Can you please share a pcap capture _and_ the selftest text output
> for
> the same failing  test?
> 
> In the log shared previously the sender had data queued at the
> mptcp-level, but not at TCP-level. In the shared pcap capture the
> receiver sends a couple of acks opening the tcp-level and mptcp-level
> window, but the sender never replies.
> 
> In such scenario the incoming ack should reach ack_update_msk() ->
> __mptcp_check_push() -> __mptcp_subflow_push_pending() (or
> mptcp_release_cb -> __mptcp_push_pending() ) -> mptcp_sendmsg_frag()
> but
> such chain is apparently broken somewhere in the failing scenario.
> Could
> you please add probe points the the mentioned funtions and perf
> record
> the test, to try to see where the mentioned chain is interrupted?

Thank you for your suggestion. I will proceed with testing accordingly.

-Geliang

> 
> Thanks,
> 
> Paolo
>