Re: [PATCH net] ieee802154: hwsim: free PIB after unregistering hardware

Hello Miquel,

After ieee802154_unregister_hw() returns, the driver callbacks that
can replace phy->pib have been quiesced, and hwsim_del() has exclusive
ownership of the final teardown. The pointer is no longer being
fetched inside an RCU read-side critical section, so rcu_dereference()
is not appropriate there.

rcu_dereference_protected(phy->pib, 1) expresses that there can no
longer be a concurrent updater at that point; the protection condition
is the completed unregister rather than a locally held lock. The value
is only fetched so the final object can be passed to kfree_rcu().

rcu_access_pointer() would also be sufficient for that limited use if
you prefer it, and I can use that spelling in a v2.

Thanks,
Yousef

On Fri, 03 Jul 2026 13:15:46 +0200, Miquel Raynal
<[email protected]> wrote:
> Hello Yousef,
>
> > @@ -1004,12 +1004,11 @@ static void hwsim_del(struct hwsim_phy *phy)
> > list_del_rcu(&e->list);
> > hwsim_free_edge(e);
> > }
> > - pib =3D rcu_dereference(phy->pib);
> > rcu_read_unlock();
> >
> > - kfree_rcu(pib, rcu);
> > -
> > ieee802154_unregister_hw(phy->hw);
> > + pib =3D rcu_dereference_protected(phy->pib, 1);
> > + kfree_rcu(pib, rcu);
> > ieee802154_free_hw(phy->hw);
> > }
>
> Would you mind justifying the choice for the _protected() version,
> please?
>
> Thanks,
> Miqu=C3=A8l