[OpenWrt-Devel] [PATCH] netifd: Improve handling of device rename

[Kristian Evensen]

Hi,

On Wed, Mar 11, 2020 at 2:13 PM Kristian Evensen
<kristian.evensen at gmail.com> wrote:
>
> After an interface has been renamed on a "fast" device (for example
> x86_64), the interface is sometimes not handled correctly by netifd.
> Looking in the logs, I see the following messages when renaming fails:
>
> Wed Mar 11 08:52:44 2020 kern.info kernel: [68383.522038] igb 0000:03:00.0 nlw_1: renamed from eth2
> Wed Mar 11 08:52:44 2020 daemon.err netifd[2739]: __device_add_user(710): Add user for device 'nlw_1', refcount=2
> Wed Mar 11 08:52:44 2020 daemon.err netifd[2739]: device_claim(413): Claim Network device nlw_1, new active count: 2
> Wed Mar 11 08:52:44 2020 daemon.err netifd[2739]: device_claim(432): claim Network device nlw_1 failed: -1
>
> Instrumenting netifd further reveals that there is a race between the hotplug
> "@move" event and ioctl(SIOCGIFINDEX). When the above error happens, the
> ioctl-call fails with ENODEV. Looking closer at the kernel code, it seems the
> hotplug-event is triggered before the renaming is completed. The easiest way to
> trigger the race, is if an interface name with the old name is not handled by
> netifd and an interface with the new name is. If only the old name is handled,
> or both names, I was not able to provoke the race.
>
> When the renaming is complete, a NEWLINK-message is generated. This patch
> modifies the logic surrounding renaming, so that we wait for the
> NEWLINK-message before marking an interface as present. The changes made are:
>
> * We only handle move-events for interfaces we know, and we return after
> device has been set as not present.
> * When we receive a NEWLINK message for an interface managed by netifd,
> we call device_set_present. device_set_present is guarded by the same
> checks as the add hotplug-event.
>
> After these changes, renaming works properly on both "fast" and "slow"
> devices. Removing a device is also handled correctly.
>
> Signed-off-by: Kristian Evensen <kristian.evensen at gmail.com>

I was wondering if anyone has had time to look at this patch and have
any opinions? I've been running the change in production since the
change was submitted, and all my renaming issues have been resolved
(and no new ones have appeared :)).

BR,
Kristian

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