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

[Bobby Eshleman <bobbyeshleman@gmail.com>]

On Tue, Sep 08, 2026 at 11:34:20AM -0700, Jakub Kicinski wrote:
> devmem.py fails on the HW runners with:
> 
>   CMD[remote]: dd if=/dev/zero bs=512 count=1 2>/dev/null | socat -b 512 \
>     -u - TCP6:[fd00:2::1]:50051,bind=[fd00:2::2]:50051,nodelay
>     STDERR: socat[41018] W bind(5, {AF=10 [fd00:2::2]:50051}, 28): \
>             Address already in use
> 
> ncdevmem installs a 5-tuple flow rule which matches the source port, so
> socat has to bind it explicitly. The port comes from rand_port(), which
> checks availability on the DUT - but we bind on the remote...
> That said the failure rate seems to high to be random collisions
> (~2% per sub-test). It's probably TIME_WAIT sockets on the remote,
> run_rx_hds() alone creates 12 of them.
> 
> Set reuseaddr so a TIME_WAIT socket does not fail the bind. Collisions
> with a live socket are still possible, we'll see if they are frequent
> enough to care.
> 
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> ---
> CC: shuah@kernel.org
> CC: bobbyeshleman@meta.com
> CC: sdf@fomichev.me
> CC: leitao@debian.org
> CC: razor@blackwall.org
> CC: linux-kselftest@vger.kernel.org
> ---
>  tools/testing/selftests/drivers/net/hw/devmem_lib.py | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> 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 ncdevmem_rx(cfg, port, verify=True, fail_on_linear=False, flow_steer=False,
>      else:
>          addr = cfg.baddr
>  
> -    suffix = f",bind={cfg.remote_baddr}:{port}"
> +    suffix = f",bind={cfg.remote_baddr}:{port},reuseaddr"
>  
>      buf = ""
>      if buf_size:
> -- 
> 2.55.0
> 

Reviewed-by: Bobby Eshleman <bobbyeshleman@meta.com>