Re: [PATCH net-next] selftests: drv-net: devmem: set reuseaddr on the sender's source port

[netdev-bot+sashiko@kernel.org]

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Critical: 0 · High: 0 · Medium: 1 · Low: 0

- [Medium] Incomplete fix: the sibling helper socat_listen() in the same
  file still has no reuse option, so the EADDRINUSE/TIME_WAIT flake the…

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selftests: drv-net: devmem: set reuseaddr on the sender's source port

The devmem selftest's sender has to bind an explicit source port on the
remote host because ncdevmem installs a 5-tuple flow rule. The port is
picked by rand_port() on the DUT, so lingering TIME_WAIT sockets on the
remote can make the bind fail with EADDRINUSE; this adds reuseaddr to the
socat bind option.

> diff --git a/tools/testing/selftests/drivers/net/hw/devmem_lib.py b/tools/testing/selftests/drivers/net/hw/devmem_lib.py
> index 3554954a6691..b6e52fa9dda5 100644
> --- a/tools/testing/selftests/drivers/net/hw/devmem_lib.py
> +++ b/tools/testing/selftests/drivers/net/hw/devmem_lib.py
> @@ -201,7 +201,7 @@ def socat_send(cfg, port, buf_size=0):
>      else:
>          addr = cfg.baddr
>  
> -    suffix = f",bind={cfg.remote_baddr}:{port}"
> +    suffix = f",bind={cfg.remote_baddr}:{port},reuseaddr"
>  
>      buf = ""
>      if buf_size:

[Severity: Medium]
Should socat_listen() in the same file get the same treatment?  It builds
the remote listener for the TX tests without any reuse option:

tools/testing/selftests/drivers/net/hw/devmem_lib.py:
    def socat_listen(cfg, port):
        """Socat listen command for TX tests."""
        return f"socat -U - TCP{cfg.addr_ipver}-LISTEN:{port}"

That command also runs on cfg.remote, and the port again comes from
rand_port(), which only binds a probe socket on the DUT.  The RX sub-tests
are what leave the TIME_WAIT sockets described in the changelog, and they
sit on remote_baddr:<port> in the same ephemeral range that rand_port()
draws from.

If run_tx() or run_tx_chunks() then draws a colliding port, the wildcard
bind of the listener conflicts with the lingering TIME_WAIT socket without
SO_REUSEADDR, socat exits, and:

    with bkg(listen_cmd, host=cfg.remote, exit_wait=True) as socat:
        wait_port_listen(port, host=cfg.remote)

times out, failing the sub-test.  Is that the same failure mode the patch
removes for the sender, just on the listener side?

For reference, the other socat listeners under drivers/net (ping.py, tso.py,
uso.py, xdp.py, xdp_metadata.py, ntuple.py) all pass ",reuseport"
explicitly, so devmem_lib.py's socat_listen() looks like the only bare one.

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Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260908183420.1369630-1-kuba%40kernel.org