Re: [Update][RFC/RFT][PATCH v3 2/5] driver core: Functional dependencies tracking support

[Lukas Wunner]

On Tue, Sep 20, 2016 at 12:46:30AM +0200, Lukas Wunner wrote:
> On Fri, Sep 16, 2016 at 02:33:55PM +0200, Rafael J. Wysocki wrote:
> > +void device_links_unbind_consumers(struct device *dev)
> > +{
> > +	struct device_link *link;
> > +	int idx;
> > +
> > + start:
> > +	idx = device_links_read_lock();
> > +
> > +	list_for_each_entry_rcu(link, &dev->links_to_consumers, s_node) {
> > +		enum device_link_status status;
> > +
> > +		if (link->flags & DEVICE_LINK_STATELESS)
> > +			continue;
> > +
> > +		spin_lock(&link->lock);
> > +		status = link->status;
> > +		if (status == DEVICE_LINK_CONSUMER_PROBE) {
> > +			spin_unlock(&link->lock);
> > +
> > +			device_links_read_unlock(idx);
> > +
> > +			wait_for_device_probe();
> > +			goto start;
> > +		}
> > +		link->status = DEVICE_LINK_SUPPLIER_UNBIND;
> > +		if (status == DEVICE_LINK_ACTIVE) {
> > +			struct device *consumer = link->consumer;
> > +
> > +			get_device(consumer);
> 
> As long as the struct device_link exists, a ref is held on the
> supplier and consumer.  Why acquire another ref here?

I'm withdrawing this particular comment as I failed to see that
device_links_read_unlock() is called next, so nothing prevents
the device link from being deleted, same for the consumer, thus
the ref needs to be acquired for device_release_driver_internal()
and this portion of Rafael's code seems perfectly correct.

Thanks & sorry for the noise,

Lukas