Subject: [PATCH 30/49] net: phylink: fix ethtool -A with attached PHYs

From: Russell King <[email-masked]>
Date: Tue, 23 Jun 2020 17:47:23 +0100

[ Upstream commit c718af2d00a37587b09e5958d142da7569f3d55b ]

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 <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 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 34ca12aec61b..b0ddeab2a8d2 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c
@@ -1519,18 +1519,20 @@ 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;
 }
-- 
2.26.2