[PATCH net-next] selftests: drv-net: Wait for bkg socat to start

[PATCH net-next] selftests: drv-net: Wait for bkg socat to start

[Mohsin Bashir]

Currently, UDP exchange is prone to failure when cmd attempt to send data
while socat in bkg is not ready. Since, the behavior is probabilistic, this
can result in flakiness for XDP tests. While testing
test_xdp_native_tx_mb() on netdevsim, a failure rate of around 1% in 500
500 iterations was observed.

Use wait_port_listen() to ensure that the bkg socat is started and ready to
receive before cmd start sending. With proposed changes, a re-run of the
same test passed 100% of time.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Mohsin Bashir <mohsin.bashr@gmail.com>
---
 tools/testing/selftests/drivers/net/xdp.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/drivers/net/xdp.py b/tools/testing/selftests/drivers/net/xdp.py
index 887d662ad128..1dd8bf3bf6c9 100755
--- a/tools/testing/selftests/drivers/net/xdp.py
+++ b/tools/testing/selftests/drivers/net/xdp.py
@@ -13,7 +13,7 @@ from enum import Enum
 
 from lib.py import ksft_run, ksft_exit, ksft_eq, ksft_ne, ksft_pr
 from lib.py import KsftFailEx, NetDrvEpEnv, EthtoolFamily, NlError
-from lib.py import bkg, cmd, rand_port
+from lib.py import bkg, cmd, rand_port, wait_port_listen
 from lib.py import ip, bpftool, defer
 
 
@@ -70,6 +70,7 @@ def _exchg_udp(cfg, port, test_string):
     tx_udp_cmd = f"echo -n {test_string} | socat -t 2 -u STDIN UDP:{cfg.baddr}:{port}"
 
     with bkg(rx_udp_cmd, exit_wait=True) as nc:
+        wait_port_listen(port, proto="udp")
         cmd(tx_udp_cmd, host=cfg.remote, shell=True)
 
     return nc.stdout.strip()
@@ -310,6 +311,7 @@ def test_xdp_native_tx_mb(cfg):
     tx_udp = f"echo {test_string} | socat -t 2 -u STDIN UDP:{cfg.baddr}:{port}"
 
     with bkg(rx_udp, host=cfg.remote, exit_wait=True) as rnc:
+        wait_port_listen(port, proto="udp", host=cfg.remote)
         cmd(tx_udp, host=cfg.remote, shell=True)
 
     stats = _get_stats(prog_info['maps']['map_xdp_stats'])
-- 
2.47.3

Re: [PATCH net-next] selftests: drv-net: Wait for bkg socat to start

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 24 Jul 2025 16:51:40 -0700 you wrote:
> Currently, UDP exchange is prone to failure when cmd attempt to send data
> while socat in bkg is not ready. Since, the behavior is probabilistic, this
> can result in flakiness for XDP tests. While testing
> test_xdp_native_tx_mb() on netdevsim, a failure rate of around 1% in 500
> 500 iterations was observed.
> 
> Use wait_port_listen() to ensure that the bkg socat is started and ready to
> receive before cmd start sending. With proposed changes, a re-run of the
> same test passed 100% of time.
> 
> [...]

Here is the summary with links:
  - [net-next] selftests: drv-net: Wait for bkg socat to start
    https://git.kernel.org/netdev/net-next/c/d1f3dbad6f0d

You are awesome, thank you!
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