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

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

[Jakub Kicinski]

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

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

[Breno Leitao]

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>

Reviewed-by: Breno Leitao <leitao@debian.org>

> --- 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"

socat_listen(), used by run_tx() and run_tx_chunks(), still builds
without reuseaddr. From my reading, I understand we don't need it given
ncdevmem does the active close on those tests. Leaving it alone seems
right.

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

[netdev-bot+sashiko]

Thank you for your contribution! Sashiko AI review found 1 potential
issue(s) to consider:

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…

--

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.

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

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

[Bobby Eshleman]

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>