netdev - [PATCH net 1/2] net: phylink: fix ethtool -A with attached PHYs

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Message-Id: <E1jnm4x-0005hV-U6@rmk-PC.armlinux.org.uk>
Date:   Tue, 23 Jun 2020 17:47:23 +0100
From:   Russell King <rmk+kernel@...linux.org.uk>
To:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH net 1/2] net: phylink: fix ethtool -A with attached PHYs

Fix a phylink's ethtool set_pauseparam support deadlock caused by phylib
interacting with phylink: we must not hold the state lock while calling
phylib functions that may call into phylink_phy_change().

Fixes: f904f15ea9b5 ("net: phylink: allow ethtool -A to change flow control advertisement")
Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>
---
 drivers/net/phy/phylink.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
index 0ab65fb75258..453f9a399bb1 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c
@@ -1502,18 +1502,20 @@ int phylink_ethtool_set_pauseparam(struct phylink *pl,
 	linkmode_set_pause(config->advertising, pause->tx_pause,
 			   pause->rx_pause);
 
-	/* If we have a PHY, phylib will call our link state function if the
-	 * mode has changed, which will trigger a resolve and update the MAC
-	 * configuration.
+	if (!pl->phydev && !test_bit(PHYLINK_DISABLE_STOPPED,
+				     &pl->phylink_disable_state))
+		phylink_pcs_config(pl, true, &pl->link_config);
+
+	mutex_unlock(&pl->state_mutex);
+
+	/* If we have a PHY, a change of the pause frame advertisement will
+	 * cause phylib to renegotiate (if AN is enabled) which will in turn
+	 * call our phylink_phy_change() and trigger a resolve.  Note that
+	 * we can't hold our state mutex while calling phy_set_asym_pause().
 	 */
-	if (pl->phydev) {
+	if (pl->phydev)
 		phy_set_asym_pause(pl->phydev, pause->rx_pause,
 				   pause->tx_pause);
-	} else if (!test_bit(PHYLINK_DISABLE_STOPPED,
-			     &pl->phylink_disable_state)) {
-		phylink_pcs_config(pl, true, &pl->link_config);
-	}
-	mutex_unlock(&pl->state_mutex);
 
 	return 0;
 }
-- 
2.20.1