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

[Yousef Alhouseen]

Agreed. I'll use rcu_access_pointer() in v2; it expresses the final
pointer fetch more directly once unregister has quiesced the updaters.

Thanks,
Yousef

On Mon, 06 Jul 2026 17:10:35 +0200, Miquel Raynal
<miquel.raynal@xxxxxxxxxxx> wrote:
> Hello Yousef,
>
> On 03/07/2026 at 04:19:42 -07, Yousef Alhouseen <alhouseenyousef@xxxxxxxxx> 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