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

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hello Yousef,

On 03/07/2026 at 04:19:42 -07, Yousef Alhouseen <alhouseenyousef@gmail.com> wrote:

> 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.

That's right.

> 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().

While I believe this is indeed true, it actually feels slightly overkill
since there is no updater anymore and, as far as I understand, the only
thing that we need here is to get the pointer value for freeing, right?

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

If you don't mind, I feel like rcu_access_pointer() is exactly what we
need here. It is also more understandable, even though I agree in
practice there are no differences in this case.

Thanks,
Miquèl