Re: [EVL] Kernel WARNING: notifier callback netevent_handler already registered

On 16.05.26 10:48, Hannes Diethelm wrote:
> Am 27.04.26 um 11:18 schrieb Florian Bezdeka:
>> On Sun, 2026-04-26 at 23:32 +0200, Hannes Diethelm wrote:
>>> Am 26.04.26 um 21:24 schrieb Philippe Gerum:
>>>> Hannes Diethelm <[email protected]> writes:
>>>>
>>>>> Am 25.04.26 um 20:50 schrieb Philippe Gerum:
>>>>>> Hannes Diethelm <[email protected]> writes:
>>>>>>
>>>>>>> Hello
>>>>>>>
>>>>>>> There is a Kernel WARNING: "notifier callback netevent_handler
>>>>>>> already registered right after boot". It is repeated 5 times.
>>>>>>>
>>>>>>> Config:
>>>>>>> Debian Trixie with xfce4 Desktop
>>>>>>> libevl: r56
>>>>>>> linux-evl: v6.12.67-evl2-rebase
>>>>>>>
>>>>>>> I traced the issue already trough the following code:
>>>>>>> net/core/net_namespace.c:355
>>>>>>> kernel/evl/net/net.c:35
>>>>>>> kernel/evl/net/ipv4/ipv4.c:41
>>>>>>> kernel/evl/net/ipv4/arp.c:323
>>>>>>>
>>>>>>> However, I lack the knowledge to do a proper fix. One way would
>>>>>>> be to just check in evl_net_init_arp() if it is already
>>>>>>> registered and don't do it more than once but that doesn't feel
>>>>>>> right.
>>>>>> It looks like the system is instantiating multiple network
>>>>>> namespaces,
>>>>>> for each of which we set up an ARP front cache by calling
>>>>>> evl_net_init_arp(). Bad idea to hook a system-wide handler there as
>>>>>> well. Could you confirm this fix [1] works for you?
>>>>>> Thanks for reporting this.
>>>>>> [1]
>>>>>> https://gitlab.com/Xenomai/xenomai4/linux-evl/-/
>>>>>> commit/569beef061321c2c00d775b13ad0aec1a1d2a416
>>>>>>
>>>>>
>>>>> Thanks, that was fast. The WARNING is gone now.
>>>>>
>>>>> But now after just updating to the kernel including your fix, I
>>>>> have a different behavior on
>>>>> incoming packages. It seams that the default when no filter is set
>>>>> has changed from EVL_RX_SKIP to EVL_RX_ACCEPT.
>>>>>
>>>>> linux-evl: v6.12.67-evl2-rebase
>>>>> -After evl net -ei enp7s0, I can ping another host.
>>>>> -oob-net-icmp does only receive packages when I use an eBPF filter
>>>>> with EVL_RX_ACCEPT
>>>>> -After that, ping doesn't work any more
>>>>>
>>>>> linux-evl: v6.12.y-cip-evl-rebase
>>>>> -After evl net -ei enp7s0, I can NOT ping another host.
>>>>> -oob-net-icmp does receive packages
>>>>> -If I use an eBPF filter returning EVL_RX_SKIP, I can ping again
>>>>>
>>>>> I am not using VLAN's.
>>>>>
>>>>> Was that changed on purpose?
>>>>
>>>> Yes, this is implemented by this commit [1]. The rationale here is that
>>>> if you turn on the oob port directly on a base device, then the evl net
>>>> stack may assume that the device is entirely dedicated to oob traffic,
>>>> as opposed to enabling such port on some upper device based on the
>>>> former (e.g. a VLAN interface). As a result, all ingress traffic
>>>> received by such base device is diverted (RX_ACCEPT) to the evl net
>>>> stack.
>>>>
>>>> [1] https://gitlab.com/Xenomai/xenomai4/linux-evl/-/
>>>> commit/3026e69cee2a1de047818fa06ad8c44623461a0d
>>>>
>>>
>>> This makes sense. It took me some time to get evl reading packages by
>>> activating an eBPF filter and it's mostly save to assume that you don't
>>> have mixed traffic on an real time network interface. With this change,
>>> a filter is not needed any more.
>>>
>>> A bit off topic:
>>>
>>> Is there anything like rtping for evl? I have seen oob-net-icmp.c but
>>> this is answering requests.
>>>
>>> In Xenomai3, there is a debian package configuration. Any interest in
>>> one for libevl? I have one working but it's still very basic. If it's
>>> presentable, I can send a patch.
>>
>> There is a debianization for x4 in xenomai-images already. See [1].
>> Can't tell why it hasn't been upstreamed yet. Maybe Tobias or Philippe
>> can comment on that.
>>
>> [1] https://gitlab.com/Xenomai/xenomai-images/-/tree/master/recipes-
>> xenomai/libevl/files/debian
> 
> Thanks for the hint. This debianization is also basic, looks like it is
> only built for
> CI purpose. But it helps to improve my version.
> 
> There are a few things missing:
> - Build dependency's

Which one? We are building the package in a clean sbuild env, so missing
build dependencies should have been revealed.

Note that Build-Depends is templated so that we could adjust it to
different libevl versions (not needed right now, though).

> - Optional: evl group + udev rules to allow non-root usage
> - Probably much more for being a install & use debian package
> 

Always open for patches to improve things. We might also move
debianization to libevl (like done for Xenomai 3) if that brings more
value to users.

Jan

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