Re: [PATCH net] net: phy: allow phy_detach() before netdev registration

[Chenguang Zhao <chenguang.zhao@linux.dev>]

On Wed, Sep 16, 2026 at 02:12:27PM +0200, Andrew Lunn wrote:
> On Wed, Sep 16, 2026 at 10:15:05AM +0800, Chenguang Zhao wrote:
> > From: Chenguang Zhao <zhaochenguang@kylinos.cn>
> > 
> > phylink_connect_phy() may be called from probe without RTNL while the
> > net_device is still NETREG_UNINITIALIZED. If PHY bring-up fails,
> > phy_detach() uses rtnl_dereference(dev->hwprov) and lockdep reports
> > suspicious RCU usage.
> 
> What do you mean by PHY bring-up?
> 
>      Andrew
Hi Andrew

PHY bring-up refers to phylink_bringup_phy(). The call chain is as follows:

usbnet_probe
  -> ax88772_bind
       -> ax88772_init_phy
            -> phylink_connect_phy
                 -> phylink_attach_phy / phy_attach_direct   // suceess 
                 -> phylink_bringup_phy                      // fail 
                 -> phy_detach                               // No RTNL
                      -> rtnl_dereference(dev->hwprov)       // lockdep warning

Because RTNL is not held when phy_detach() is called, rtnl_dereference() triggers a lockdep warning.

Thanks
Chenguang