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

[Andrew Lunn <andrew@lunn.ch>]

On Thu, Sep 17, 2026 at 03:06:46PM +0800, Chenguang Zhao wrote:
> 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.

Lets zoom out and look at the big picture....

Why is phy_detach() not symmetric with phy_attach()?

Why is phy_detach() touching dev->hwprov, when phy_attach() does not?

Where is dev->hwprov set and why is the mirror function not dealing
with this?

     Andrew