Re: [PATCH net-next 6/6] net: document NETDEV_UNREGISTER unlocked rationale

[Stanislav Fomichev <sdf.kernel@gmail.com>]

On 06/30, Jakub Kicinski wrote:
> On Tue, 30 Jun 2026 11:21:29 -0700 Stanislav Fomichev wrote:
> > +Many ``NETDEV_UNREGISTER`` handlers release their lowers with
> > +``dev_close()``, which takes the instance lock itself. Holding
> > +the lock across UNREGISTER would deadlock.
> > +
> > +Moving UNREGISTER under the lock is mechanical: switch those
> > +callers to the ``netif_*()`` lock-held variants. Deferred to
> > +limit churn.


> Doing anything with the device that is sending the UNREGISTER
> sounds odd, since it's going away..

Looking at __bond_release_one, it does try to restore a few original
settings, mostly mtu, I think? (And it does call dev_close unconditionally,
that's fixable).

bond_netdev_event
  bond_slave_netdev_event(slave_dev=event_dev)
    __bond_release_one
      {__netif,dev}_set_mtu(slave_dev, slave->original_mtu)

Or am I misreading this part?

> Not following TBH. Let's say there's a UNREGISTER ntf for eth0.
> Are you saying that eg. vlan which closes their own vlan0 devices
> on top of eth0 needs to be switched to netif_ ? That wouldn't make
> sense since the notification is holding netdev_lock(eth0) and
> we're talking about netif_close(vlan0)?

Maybe rewording it to `... UNREGISTER handlers interact with their
lowers using dev_xxx handlers which take the instance lock` ?

I'm mainly looking for an excuse/explanation on why UNREGISTER
is not converted in this series. Or should I bite the bullet and
add a few patches to make UNREGISTER ops locked as well?