Re: [PATCH net] net: usb: lan78xx: only stop phylink if the interface is running

[YuanZhe Liu]

On Fri, Oct 30, 2026 at 04:02:36PM +0000, sashiko-bot@xxxxxxxxxx wrote:
> Does calling phylink_stop() and phylink_disconnect_phy() before
> unregister_netdev(net) in drivers/net/usb/lan78xx.c:lan78xx_disconnect()
> cause out-of-order teardown, a duplicate phylink_stop() call, and a race
> window when rtnl_lock() is dropped?

Yes, the ordering is wrong. v2 drops the explicit phylink_stop() from the
disconnect path and unregisters the net device first:

	unregister_netdev(net);

	rtnl_lock();
	phylink_disconnect_phy(dev->phylink);
	rtnl_unlock();

unregister_netdev() closes a running device, so phylink_stop() is done by
lan78xx_stop() with dev->dev_mutex held and after the TX/RX URBs have been
terminated, which is the same sequence as a normal ifdown. When the
interface was never started no phylink_stop() happens at all, and that is
exactly the case phy_stop() complains about with "called from state READY".

This also removes the second phylink_stop() invocation and the window in
which the net device was still registered with no PHY attached.

On the remaining points:

- The duplicate phylink_stop() was harmless in practice, because after
  phylink_disconnect_phy() pl->phydev is NULL and PHYLINK_DISABLE_STOPPED
  is already set. It is gone now anyway.

- The PHY interrupt is not released by phylink_disconnect_phy(). The virq
  created by irq_create_mapping() is disposed in lan78xx_remove_irq_domain(),
  called from lan78xx_unbind(), which also clears dev->domain_data.phyirq;
  lan78xx_status() tests that field before generic_handle_irq_safe(). The
  intr URB is killed later in lan78xx_disconnect(), and that ordering is
  unchanged by this patch.

- Andrew also asked why the Fixes tag points at e110bc825897: that commit
  added both the phylink instance and the unconditional phylink_stop() call
  in lan78xx_disconnect(), and

    git log -S'phylink_stop(dev->phylink)' -- drivers/net/usb/lan78xx.c

  shows that the line has not been touched since.

v2 is sent as a separate thread.

Thanks,
YuanZhe