Re: [PATCH net v2] net: Lock lower level devices when updating features

[Stanislav Fomichev <stfomichev@gmail.com>]

On 05/08, Cosmin Ratiu wrote:
> On Thu, 2025-05-08 at 09:12 -0700, Stanislav Fomichev wrote:
> > > --- a/net/core/dev.c
> > > +++ b/net/core/dev.c
> > > @@ -10454,7 +10454,9 @@ static void
> > > netdev_sync_lower_features(struct net_device *upper,
> > >  			netdev_dbg(upper, "Disabling feature %pNF
> > > on lower dev %s.\n",
> > >  				   &feature, lower->name);
> > >  			lower->wanted_features &= ~feature;
> > > +			netdev_lock_ops(lower);
> > >  			__netdev_update_features(lower);
> > > +			netdev_unlock_ops(lower);
> > >  
> > >  			if (unlikely(lower->features & feature))
> > >  				netdev_WARN(upper, "failed to
> > > disable %pNF on %s!\n",
> > 
> > Any reason not to cover the whole section under the if()? For
> > example,
> > looking at netdev_features_change, most of its invocations are under
> > the
> > lock, so keeping the lock around it might help with consistency (and
> > we can clarify it as such in
> > Documentation/networking/netdevices.rst).
> > Plus, wanted_features is already sort of ops-protected (looking at
> > netif_disable_lro+dev_disable_lro).
> 
> The critical section could be extended for the whole if, but there are
> a lot of netdev_features_change() calls in many drivers, which I am not
> sure are ops protected. So I'd be reluctant to state that
> NETDEV_FEAT_CHANGE is ops-protected in
> Documentation/networking/netdevices.rst, even though all core
> invocations would be made with the ops lock held.

Ack, I don't think the calls in drivers/ matter, none of these are
ops-protected drivers, but we can do that separately.