linux-kernel - Re: [PATCH v2 net 1/2] net: phylink: add lock for serializing concurrent pl->phydev writes with resolver

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Message-ID: <20250903153120.4oiwyz6bxfj3fuuv@skbuf>
Date: Wed, 3 Sep 2025 18:31:20 +0300
From: Vladimir Oltean <vladimir.oltean@....com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
	Heiner Kallweit <hkallweit1@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 net 1/2] net: phylink: add lock for serializing
 concurrent pl->phydev writes with resolver

On Wed, Sep 03, 2025 at 04:26:35PM +0100, Russell King (Oracle) wrote:
> On Wed, Sep 03, 2025 at 06:23:47PM +0300, Vladimir Oltean wrote:
> > @@ -2305,6 +2314,7 @@ void phylink_disconnect_phy(struct phylink *pl)
> >  
> >  	phy = pl->phydev;
> >  	if (phy) {
> > +		mutex_lock(&pl->phy_lock);
> 
> If we can, I think it would be better to place this a couple of lines
> above and move the unlock.

Sorry for potentially misunderstanding, do you mean like this?

	mutex_lock(&pl->phy_lock);
	phy = pl->phydev;
	if (phy) {
		mutex_lock(&phy->lock);
		mutex_lock(&pl->state_mutex);
		pl->phydev = NULL;
		pl->phy_enable_tx_lpi = false;
		pl->mac_tx_clk_stop = false;
		mutex_unlock(&pl->state_mutex);
		mutex_unlock(&phy->lock);
		mutex_unlock(&pl->phy_lock);
		flush_work(&pl->resolve);

		phy_disconnect(phy);
	} else {
		mutex_unlock(&pl->phy_lock);
	}

move the unlock where? because flush_work(&pl->resolve) needs to happen
unlocked, otherwise we'll deadlock with phylink_resolve().

Additionally, dereferincing pl->phydev under rtnl_lock() is already safe,
and doesn't need the secondary clock.