Re: [PATCH net 4/4] selftests: net: add SCTP I-FORWARD-TSN tests with message interleaving

[Tim Budding <tim.budding@gmail.com>]

On Sun, 25 Oct 2026 12:08:49 +0000, netdev-bot+sashiko@kernel.org wrote:
> [Severity: Low]
> This isn't a bug, but the deadline check and the poll() timeout use two
> separate now_ms() samples. If end - now_ms() comes out negative, poll()
> blocks with no timeout.

Agreed, I'll fix it in v2.

> [Severity: Low]
> Does the reset case check that queued I-DATA is discarded on reset?

[...]

> The test does show that MIDs restart at 0, because the marker is
> delivered. Could the test leave stale fragments, or a message in partial
> delivery, pending on the server when the reset is issued?

Agreed. As it stands, the reset test only shows that the reset
completes and that MIDs start again from 0. A reset is only performed
when the data sender has nothing outstanding, so in v2 the pending data
will come from two PR-SCTP messages that the client abandons while nft
drops the I-FORWARD-TSN: one partly received on stream 0 and one in
partial delivery on stream 1. The reset is requested once by the server
and once by the client, so that both new abort_pd() calls are covered.
The test then checks for SCTP_PARTIAL_DELIVERY_ABORTED on stream 1,
that RX_QUEUE is 0, and that a new fragmented message on stream 0,
which reuses MID 0, is delivered intact.

> [Severity: Medium]
> Can the RX_QUEUE check fail on a correct kernel in the ordered and
> unordered tests?

[...]

> Should this poll assoc_rx_queue() until it reaches 0, with a timeout?
> Or wait for some sign on the server that the I-FORWARD-TSN was
> processed?

Yes, confirmed. Lowering net.core.wmem_default alone wasn't enough:
there were no failures in 140 runs between 212992 and 66000. small is
then sent after all of big, but Nagle holds the marker back until small
is abandoned, and it then goes out in the same packet as the
I-FORWARD-TSN, behind it. With SCTP_NODELAY on the client and
wmem_default=70000, the ordered and unordered tests fail 10 times out
of 10 with "2464 bytes left queued on the association": the marker
goes out right after small, and the I-FORWARD-TSN follows one RTO
(300 ms) later.

Rather than poll RX_QUEUE, v2 will have the client wait (with a
timeout) until all of its data has been acked, i.e. until SCTP_STATUS
sstat_unackdata is 0, and then check RX_QUEUE once. The server's
cumulative TSN can only move past the abandoned TSN once it has
processed the I-FORWARD-TSN, so the check no longer depends on timing.