netdev - Re: [PATCH net-next v3] net: phy: Fix suspicious rcu

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Message-ID: <20250121103845.6e135477@kmaincent-XPS-13-7390>
Date: Tue, 21 Jan 2025 10:38:45 +0100
From: Kory Maincent <kory.maincent@...tlin.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, Claudiu Beznea
 <claudiu.beznea.uj@...renesas.com>, thomas.petazzoni@...tlin.com, Andrew
 Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>, Russell King
 <linux@...linux.org.uk>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni
 <pabeni@...hat.com>
Subject: Re: [PATCH net-next v3] net: phy: Fix suspicious rcu_dereference
 usage

On Mon, 20 Jan 2025 11:12:28 -0800
Jakub Kicinski <kuba@...nel.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