Re: [PATCH net-next v7 04/12] net: hold netdev instance lock during rtnetlink operations

[Stanislav Fomichev <stfomichev@gmail.com>]

On 02/25, Jakub Kicinski wrote:
> On Mon, 24 Feb 2025 10:08:00 -0800 Stanislav Fomichev wrote:
> > +static inline int netdev_lock_cmp_fn(const struct lockdep_map *a,
> > +				     const struct lockdep_map *b)
> > +{
> > +	/* Only lower devices currently grab the instance lock, so no
> > +	 * real ordering issues can occur. In the near future, only
> > +	 * hardware devices will grab instance lock which also does not
> > +	 * involve any ordering. Suppress lockdep ordering warnings
> > +	 * until (if) we start grabbing instance lock on pure SW
> > +	 * devices (bond/team/veth/etc).
> > +	 */
> > +	return -1;
> 
> Does this no kill all lockdep warnings?

Initially I was gonna say "no" because I've seen (and do see) deadlock
warnings with netdevsim, but looking at the code I think you're right.

And netdevsim doesn't call netdev_lockdep_set_classes :-/ I think we want
to add that as well?

I will make cmp_fn be:
if (a == b)
	return 0;
return -1;

That should bring back deadlock detection for the rest for the sw
drivers.