[PATCH net] net: phy: mscc: fix deadlock in phy_ethtool_{get,set}_wol()

[Vladimir Oltean]

Since the blamed commit, phy_ethtool_get_wol() and phy_ethtool_set_wol()
acquire phydev->lock, but the mscc phy driver implementations,
vsc85xx_wol_get() and vsc85xx_wol_set(), acquire the same lock as well,
resulting in a deadlock.

$ ip link set swp3 down
============================================
WARNING: possible recursive locking detected
mscc_felix 0000:00:00.5 swp3: Link is Down
--------------------------------------------
ip/375 is trying to acquire lock:
ffff3d7e82e987a8 (&dev->lock){+.+.}-{4:4}, at: vsc85xx_wol_get+0x2c/0xf4

but task is already holding lock:
ffff3d7e82e987a8 (&dev->lock){+.+.}-{4:4}, at: phy_ethtool_get_wol+0x3c/0x6c

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&dev->lock);
  lock(&dev->lock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by ip/375:
 #0: ffffd43b2a955788 (rtnl_mutex){+.+.}-{4:4}, at: rtnetlink_rcv_msg+0x144/0x58c
 #1: ffff3d7e82e987a8 (&dev->lock){+.+.}-{4:4}, at: phy_ethtool_get_wol+0x3c/0x6c

Call trace:
 __mutex_lock+0x98/0x454
 mutex_lock_nested+0x2c/0x38
 vsc85xx_wol_get+0x2c/0xf4
 phy_ethtool_get_wol+0x50/0x6c
 phy_suspend+0x84/0xcc
 phy_state_machine+0x1b8/0x27c
 phy_stop+0x70/0x154
 phylink_stop+0x34/0xc0
 dsa_port_disable_rt+0x2c/0xa4
 dsa_slave_close+0x38/0xec
 __dev_close_many+0xc8/0x16c
 __dev_change_flags+0xdc/0x218
 dev_change_flags+0x24/0x6c
 do_setlink+0x234/0xea4
 __rtnl_newlink+0x46c/0x878
 rtnl_newlink+0x50/0x7c
 rtnetlink_rcv_msg+0x16c/0x58c

Removing the mutex_lock(&phydev->lock) calls from the driver restores
the functionality.

Fixes: 2f987d486610 ("net: phy: Add locks to ethtool functions")
Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
---
 drivers/net/phy/mscc/mscc_main.c | 24 ++++++++----------------
 1 file changed, 8 insertions(+), 16 deletions(-)

diff --git a/drivers/net/phy/mscc/mscc_main.c b/drivers/net/phy/mscc/mscc_main.c
index 8a13b1ad9a33..62bf99e45af1 100644
--- a/drivers/net/phy/mscc/mscc_main.c
+++ b/drivers/net/phy/mscc/mscc_main.c
@@ -280,12 +280,9 @@ static int vsc85xx_wol_set(struct phy_device *phydev,
 	u16 pwd[3] = {0, 0, 0};
 	struct ethtool_wolinfo *wol_conf = wol;
 
-	mutex_lock(&phydev->lock);
 	rc = phy_select_page(phydev, MSCC_PHY_PAGE_EXTENDED_2);
-	if (rc < 0) {
-		rc = phy_restore_page(phydev, rc, rc);
-		goto out_unlock;
-	}
+	if (rc < 0)
+		return phy_restore_page(phydev, rc, rc);
 
 	if (wol->wolopts & WAKE_MAGIC) {
 		/* Store the device address for the magic packet */
@@ -323,7 +320,7 @@ static int vsc85xx_wol_set(struct phy_device *phydev,
 
 	rc = phy_restore_page(phydev, rc, rc > 0 ? 0 : rc);
 	if (rc < 0)
-		goto out_unlock;
+		return rc;
 
 	if (wol->wolopts & WAKE_MAGIC) {
 		/* Enable the WOL interrupt */
@@ -331,22 +328,19 @@ static int vsc85xx_wol_set(struct phy_device *phydev,
 		reg_val |= MII_VSC85XX_INT_MASK_WOL;
 		rc = phy_write(phydev, MII_VSC85XX_INT_MASK, reg_val);
 		if (rc)
-			goto out_unlock;
+			return rc;
 	} else {
 		/* Disable the WOL interrupt */
 		reg_val = phy_read(phydev, MII_VSC85XX_INT_MASK);
 		reg_val &= (~MII_VSC85XX_INT_MASK_WOL);
 		rc = phy_write(phydev, MII_VSC85XX_INT_MASK, reg_val);
 		if (rc)
-			goto out_unlock;
+			return rc;
 	}
 	/* Clear WOL iterrupt status */
 	reg_val = phy_read(phydev, MII_VSC85XX_INT_STATUS);
 
-out_unlock:
-	mutex_unlock(&phydev->lock);
-
-	return rc;
+	return 0;
 }
 
 static void vsc85xx_wol_get(struct phy_device *phydev,
@@ -358,10 +352,9 @@ static void vsc85xx_wol_get(struct phy_device *phydev,
 	u16 pwd[3] = {0, 0, 0};
 	struct ethtool_wolinfo *wol_conf = wol;
 
-	mutex_lock(&phydev->lock);
 	rc = phy_select_page(phydev, MSCC_PHY_PAGE_EXTENDED_2);
 	if (rc < 0)
-		goto out_unlock;
+		goto out_restore_page;
 
 	reg_val = __phy_read(phydev, MSCC_PHY_WOL_MAC_CONTROL);
 	if (reg_val & SECURE_ON_ENABLE)
@@ -377,9 +370,8 @@ static void vsc85xx_wol_get(struct phy_device *phydev,
 		}
 	}
 
-out_unlock:
+out_restore_page:
 	phy_restore_page(phydev, rc, rc > 0 ? 0 : rc);
-	mutex_unlock(&phydev->lock);
 }
 
 #if IS_ENABLED(CONFIG_OF_MDIO)
-- 
2.34.1