Pi3b+: "kevent 4 may have been dropped" with lan78xx

[jens-maus]

Every second or third boot with a 4.14.26 kernel where the LAN78XX support had been enabled I receive the following notices in dmesg:

...
[   16.345186] lan78xx 1-1.1.1:1.0 eth0: kevent 4 may have been dropped
[   16.346150] lan78xx 1-1.1.1:1.0 eth0: kevent 4 may have been dropped
[   16.347155] lan78xx 1-1.1.1:1.0 eth0: kevent 4 may have been dropped
[   16.348168] lan78xx 1-1.1.1:1.0 eth0: kevent 4 may have been dropped
[   16.349165] lan78xx 1-1.1.1:1.0 eth0: kevent 4 may have been dropped
[   16.350173] lan78xx 1-1.1.1:1.0 eth0: kevent 4 may have been dropped
[   16.351150] lan78xx 1-1.1.1:1.0 eth0: kevent 4 may have been dropped
[   16.352149] lan78xx 1-1.1.1:1.0 eth0: kevent 4 may have been dropped
[   16.353164] lan78xx 1-1.1.1:1.0 eth0: kevent 4 may have been dropped
[   16.354165] lan78xx 1-1.1.1:1.0 eth0: kevent 4 may have been dropped
[   16.355150] lan78xx 1-1.1.1:1.0 eth0: kevent 4 may have been dropped
...

Sometimes the system still continues and is able to setup eth0 properly. However, every now and then the system is not able to bring up eth0 and thus the boot up process is interrupted.

Any idea where this might come from or how to debug this situation?

[JamesH65]

Bugger, thought the kevent issue was ancient history. IIRC, it is because an event is stuck on the system event queue and then another one turns up before it is serviced. But it's not been reported for a couple of years, and that was on the smsc75xx driver. Not sure this is the same thing though, might be a systemd initialisation issue.

[jens-maus]

The system I am developing and compiling the raspberrypi kernel for is not using systemd at all but is based on buildroot without systemd.

[JamesH65]

OK, do you get the same problem with Raspbian?

[jens-maus]

Haven‘t tested it yet with Raspbian. However, this is the kernel defconfig I am using:

https://github.com/jens-maus/RaspberryMatic/blob/master/buildroot-external/board/raspberrypi3/kernel_defconfig

[Bilg21]

I have the same issue with Compute Module 3. But it looks like a hardware issue. It's not happening on another setup which is identical.

[danijelt]

I am also using Buildroot to make my own image, and I managed to resolve this issue by disabling VLAN support in kernel.
In my case, I do have systemd, and this message appears after systemd starts hostname service:

[  OK  ] Started Hostname Service.
[   17.326467] lan78xx 1-1.1.1:1.0 eth0: kevent 4 may have been dropped
[   17.326507] 8021q: adding VLAN 0 to HW filter on device eth0
[   17.338617] lan78xx 1-1.1.1:1.0 eth0: kevent 4 may have been dropped
[   17.345081] lan78xx 1-1.1.1:1.0 eth0: kevent 4 may have been dropped

After disabling VLAN support (CONFIG_BRIDGE_VLAN_FILTERING, CONFIG_VLAN_8021Q and CONFIG_VLAN_8021Q_GVRP) in latest rpi-4.14-y (4.14.33) this message stopped appearing almost completely, and I don't have the lockup bug anymore.

Firmware is ae9a493932e47e08cabb25a2728037298075fd00 and userland is a343dcad1dae4e93f4bfb99496697e207f91027e.

[JamesH65]

@danijelt @jens-maus We have committed three or four fixes to VLAN support in the lan78xx driver since 4.14.33, so its probably worth getting the latest kernel and seeing if it has fixed the kevent issue with VLAN enabled. There are also other lan78xx fixes in there, so well worth trying to see if the kevent issues has gone.

If you do find it has gone, please close this issue.

[JamesH65]

@danijelt @jens-maus If no further reports/updates are forthcoming, I'm inclined to close this report.

[danijelt]

We have released a stable production image without VLAN and I'm currently occupied with another project.

I'll keep this in mind during the next update and report here if kevent/VLAN issue persists.

[fhunleth]

I was able to easily reproduce this issue with the VLAN options disabled when running Linux 4.14.29 at commit c117a8b. I just tried updating to the latest rpi-4.14-y (4.14.44) at commit 4fca48b, and I can no longer reproduce the kevent 4 issue.

[bcutter]

I also saw this some times on my Pi 3 B+. Currently the Pi is completely dead, on console screen the

"** 1 printk messages dropped ** [ 3808.632569] lan78xx 1-1.1.1:1.0 eth0: kevent 4 may have been dropped"

messages go wild meaning every second about 50 of those lines are shown. Only one option: hard reset of the system. Resulting in fsck errors and so on.

Raspbian Stretch by the way. 1 Gbit/s ethernet port.
Anything I can do on this? Will there be a fix? A workaround?

[JamesH65]

@bcutter Are you using the latest kernel? You can apt update, to get an official release, or rpi-update to get the latest bleeding edge one. You might need rpi-update, but backup first. There have been a number of kernel updates so worth trying.