topic 回复： imx8mp router loopback, causing NETDEV WATCHDOG to reset and unable to restore the mac in i.MX Processors

imx8mp router loopback, causing NETDEV WATCHDOG to reset and unable to restore the mac

yrj — Fri, 25 Jul 2025 01:38:05 GMT

Hello, may I ask if our A board and B board are connected to the switch at the same time, and then A-B mutual ping, the switch has a ring network due to misoperation (both ends of a network cable are connected to the switch), there is a problem with the kernel (direct restart, or debug is stuck, etc.), the detailed log is in the attachment.

[ 314.850236] ------------[ cut here ]------------
[ 314.854871] NETDEV WATCHDOG: ens3 (fec): transmit queue 0 timed out 3384 ms
[ 314.861910] WARNING: CPU: 0 PID: 15 at net/sched/sch_generic.c:525 dev_watchdog+0x234/0x23c
[ 314.870271] Modules linked in:
[ 314.873329] CPU: 0 PID: 15 Comm: ksoftirqd/0 Not tainted 6.6.3-g9d3450dbcab9-dirty #71
[ 314.881246] Hardware name: NXP i.MX8MPlus EVK board (DT)
[ 314.886555] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 314.893516] pc : dev_watchdog+0x234/0x23c
[ 314.897528] lr : dev_watchdog+0x234/0x23c
[ 314.901538] sp : ffff8000823e3c20
[ 314.904850] x29: ffff8000823e3c20 x28: 0000000000000100 x27: ffff8000823e3cd0
[ 314.911989] x26: ffff8000820d69c0 x25: 0000000000000d38 x24: ffff8000820d6000
[ 314.919128] x23: 0000000000000000 x22: ffff0000055503dc x21: ffff000005550000
[ 314.926266] x20: ffff00000589c400 x19: ffff000005550488 x18: 0000000000000006
[ 314.933404] x17: ffff8000821b62e8 x16: 0000000073e4d9ea x15: ffff8000823e3640
[ 314.940541] x14: 0000000000000000 x13: ffff8000820f0da0 x12: 0000000000000672
[ 314.947679] x11: 0000000000000226 x10: ffff800082148da0 x9 : ffff8000820f0da0
[ 314.954818] x8 : 00000000ffffefff x7 : ffff800082148da0 x6 : 80000000fffff000
[ 314.961956] x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000000000
[ 314.969093] x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff00000412d880

回复： imx8mp router loopback, causing NETDEV WATCHDOG to reset and unable to restore the mac

yrj — Fri, 25 Jul 2025 01:45:52 GMT

内核版本是：6.6.3

回复： imx8mp router loopback, causing NETDEV WATCHDOG to reset and unable to restore the mac

Zhiming_Liu — Fri, 25 Jul 2025 02:49:12 GMT

Hi @yrj

这个问题更多得是和交换机有关，建议通过交换机的环路检测功能解决环网问题。

Best Regards,
Zhiming

回复： imx8mp router loopback, causing NETDEV WATCHDOG to reset and unable to restore the mac

yrj — Fri, 25 Jul 2025 02:54:49 GMT

Hi @Zhiming_Liu

不小心造成环路，imx8mp可以预防吗

回复： imx8mp router loopback, causing NETDEV WATCHDOG to reset and unable to restore the mac

Zhiming_Liu — Fri, 25 Jul 2025 05:35:18 GMT

Hi,

最佳的方法是交换机侧设置防御，一般都有这种功能，可以参考这个：

https://www.cisco.com/c/zh_cn/support/docs/smb/switches/cisco-250-series-smart-switches/smb5794-enable-loopback-detection-on-a-switch.html

当然也可以在驱动层添加广播检测统计，但是目前fec驱动不支持这项功能。

你可以通过一个脚本在用户层监测广播，如果出现大量广播，就把网卡down掉。

Best Regards,
Zhiming

回复： imx8mp router loopback, causing NETDEV WATCHDOG to reset and unable to restore the mac

yrj — Fri, 25 Jul 2025 09:16:19 GMT

Hi @Zhiming_Liu

网络风暴发生时，系统有概率直接重启，或者debug调试口卡死，或者系统跑飞（如b.log），需要重启才能恢复。