Describe the bug

FYI - since kernel 6.15 there may be a lot of network connectivity issues (transmit queue lockup) on the Pi4/CM4 triggered by having traffic coming from both the kernel and a user space application at the same time - like if the pi is setup as a router and file server.

I don't have time to look into it myself, but I have notified the maintainers of the bcmgenet driver and as far as I know it has not yet been fixed - https://lists.openwall.net/netdev/2025/06/27/261

Steps to reproduce the behaviour

Configure Pi as a router (or something where the kernel sends packets)
Setup a file server or iperf3 (some user space application that can send packets)
Transmit kernel and user space traffic out of the BCM interface at gigabit speed

Device (s)

Raspberry Pi CM4, Raspberry Pi CM4 Lite, Raspberry Pi 4 Mod. B

System

Raspberry Pi reference 2024-11-19
Generated using pi-gen, https://github.com/RPi-Distro/pi-gen, 891df1e21ed2b6099a2e6a13e26c91dea44b34d4, stage2

Mar 19 2025 18:24:21
Copyright (c) 2012 Broadcom
version ca6e8171a80ea46924ffaa629250bfb482f3a02c (clean) (release) (start)

Linux router.localnet 6.12.25-v8-ZAK+ #1 SMP PREEMPT Sat Apr 26 13:37:08 BST 2025 aarch64 GNU/Linux

Logs

Jun 26 14:32:06 router.localnet kernel: bcmgenet fd580000.ethernet
lan0: NETDEV WATCHDOG: CPU: 1: transmit queue 0 timed out 2004 ms
Jun 26 14:32:08 router.localnet kernel: bcmgenet fd580000.ethernet
lan0: NETDEV WATCHDOG: CPU: 1: transmit queue 4 timed out 2004 ms
Jun 26 14:32:09 router.localnet kernel: bcmgenet fd580000.ethernet
lan0: NETDEV WATCHDOG: CPU: 2: transmit queue 3 timed out 2004 ms
Jun 26 14:32:10 router.localnet kernel: bcmgenet fd580000.ethernet
lan0: NETDEV WATCHDOG: CPU: 1: transmit queue 3 timed out 2892 ms
Jun 26 14:32:11 router.localnet kernel: bcmgenet fd580000.ethernet
lan0: NETDEV WATCHDOG: CPU: 2: transmit queue 3 timed out 3884 ms
Jun 26 14:32:12 router.localnet kernel: bcmgenet fd580000.ethernet
lan0: NETDEV WATCHDOG: CPU: 0: transmit queue 1 timed out 2208 ms
Jun 26 14:32:13 router.localnet kernel: bcmgenet fd580000.ethernet
lan0: NETDEV WATCHDOG: CPU: 1: transmit queue 1 timed out 3232 ms
Jun 26 14:32:14 router.localnet kernel: bcmgenet fd580000.ethernet
lan0: NETDEV WATCHDOG: CPU: 1: transmit queue 1 timed out 4224 ms
Jun 26 14:32:15 router.localnet kernel: bcmgenet fd580000.ethernet
lan0: NETDEV WATCHDOG: CPU: 2: transmit queue 1 timed out 5216 ms

Additional context

No response