Re: [PATCH net-next v3] net: phy: Fix suspicious rcu_dereference usage

[Kory Maincent <kory.maincent@bootlin.com>]

On Mon, 20 Jan 2025 11:12:28 -0800
Jakub Kicinski <kuba@kernel.org> wrote:

> On Mon, 20 Jan 2025 15:19:25 +0100 Kory Maincent wrote:
> > The path reported to not having RTNL lock acquired is the suspend path of
> > the ravb MAC driver. Without this fix we got this warning:  
> 
> I maintain that ravb is buggy, plenty of drivers take rtnl_lock 
> from the .suspend callback. We need _some_ write protection here,
> the patch as is only silences a legitimate warning.

Indeed if the suspend path is buggy we should fix it. Still there is lots of
ethernet drivers calling phy_disconnect without rtnl (IIUC) if probe return an
error or in the remove path. What should we do about it?

About ravb suspend, I don't have the board, Claudiu could you try this instead
of the current fix:

diff --git a/drivers/net/ethernet/renesas/ravb_main.c
b/drivers/net/ethernet/renesas/ravb_main.c index bc395294a32d..c9a0d2d6f371
100644 --- a/drivers/net/ethernet/renesas/ravb_main.c
+++ b/drivers/net/ethernet/renesas/ravb_main.c
@@ -3215,15 +3215,22 @@ static int ravb_suspend(struct device *dev)
        if (!netif_running(ndev))
                goto reset_assert;
 
+       rtnl_lock();
        netif_device_detach(ndev);
 
-       if (priv->wol_enabled)
-               return ravb_wol_setup(ndev);
+       if (priv->wol_enabled) {
+               ret = ravb_wol_setup(ndev);
+               rtnl_unlock();
+               return ret;
+       }
 
        ret = ravb_close(ndev);
-       if (ret)
+       if (ret) {
+               rtnl_unlock();
                return ret;
+       }
 
+       rtnl_unlock();
        ret = pm_runtime_force_suspend(&priv->pdev->dev);
        if (ret)
                return ret;

Regards,
-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com