[PATCH net] net: dsa: remove redundant netdev_lock_ops() from conduit ethtool ops

[Stanislav Fomichev <sdf.kernel@gmail.com>]

DSA replaces the conduit (master) device's ethtool_ops with its own
wrappers that aggregate stats from both the conduit and DSA switch
ports. Taking the lock again inside the DSA wrappers causes a deadlock.

Stumbled upon this when booting qemu with fbnic and CONFIG_NET_DSA_LOOP=y
(which looks like some kind of testing device that auto-populates the ports
of eth0). `ethtool -i` is enough to deadlock. This means we have basically zero
coverage for DSA stuff with real ops locked devs.

Remove the redundant netdev_lock_ops()/netdev_unlock_ops() calls from
the DSA conduit ethtool wrappers.

Cc: Maxime Chevallier <maxime.chevallier@bootlin.com>
Fixes: 2bcf4772e45a ("net: ethtool: try to protect all callback with netdev instance lock")
Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
(cherry picked from commit 1538c00ab3212273240112bd53692d54d95f2dd5)
---
 net/dsa/conduit.c | 16 +---------------
 1 file changed, 1 insertion(+), 15 deletions(-)

diff --git a/net/dsa/conduit.c b/net/dsa/conduit.c
index a1b044467bd6..8398d72d7e4d 100644
--- a/net/dsa/conduit.c
+++ b/net/dsa/conduit.c
@@ -27,9 +27,7 @@ static int dsa_conduit_get_regs_len(struct net_device *dev)
 	int len;
 
 	if (ops && ops->get_regs_len) {
-		netdev_lock_ops(dev);
 		len = ops->get_regs_len(dev);
-		netdev_unlock_ops(dev);
 		if (len < 0)
 			return len;
 		ret += len;
@@ -60,15 +58,11 @@ static void dsa_conduit_get_regs(struct net_device *dev,
 	int len;
 
 	if (ops && ops->get_regs_len && ops->get_regs) {
-		netdev_lock_ops(dev);
 		len = ops->get_regs_len(dev);
-		if (len < 0) {
-			netdev_unlock_ops(dev);
+		if (len < 0)
 			return;
-		}
 		regs->len = len;
 		ops->get_regs(dev, regs, data);
-		netdev_unlock_ops(dev);
 		data += regs->len;
 	}
 
@@ -115,10 +109,8 @@ static void dsa_conduit_get_ethtool_stats(struct net_device *dev,
 	int count, mcount = 0;
 
 	if (ops && ops->get_sset_count && ops->get_ethtool_stats) {
-		netdev_lock_ops(dev);
 		mcount = ops->get_sset_count(dev, ETH_SS_STATS);
 		ops->get_ethtool_stats(dev, stats, data);
-		netdev_unlock_ops(dev);
 	}
 
 	list_for_each_entry(dp, &dst->ports, list) {
@@ -149,10 +141,8 @@ static void dsa_conduit_get_ethtool_phy_stats(struct net_device *dev,
 		if (count >= 0)
 			phy_ethtool_get_stats(dev->phydev, stats, data);
 	} else if (ops && ops->get_sset_count && ops->get_ethtool_phy_stats) {
-		netdev_lock_ops(dev);
 		count = ops->get_sset_count(dev, ETH_SS_PHY_STATS);
 		ops->get_ethtool_phy_stats(dev, stats, data);
-		netdev_unlock_ops(dev);
 	}
 
 	if (count < 0)
@@ -176,13 +166,11 @@ static int dsa_conduit_get_sset_count(struct net_device *dev, int sset)
 	struct dsa_switch_tree *dst = cpu_dp->dst;
 	int count = 0;
 
-	netdev_lock_ops(dev);
 	if (sset == ETH_SS_PHY_STATS && dev->phydev &&
 	    (!ops || !ops->get_ethtool_phy_stats))
 		count = phy_ethtool_get_sset_count(dev->phydev);
 	else if (ops && ops->get_sset_count)
 		count = ops->get_sset_count(dev, sset);
-	netdev_unlock_ops(dev);
 
 	if (count < 0)
 		count = 0;
@@ -239,7 +227,6 @@ static void dsa_conduit_get_strings(struct net_device *dev, u32 stringset,
 	struct dsa_switch_tree *dst = cpu_dp->dst;
 	int count, mcount = 0;
 
-	netdev_lock_ops(dev);
 	if (stringset == ETH_SS_PHY_STATS && dev->phydev &&
 	    !ops->get_ethtool_phy_stats) {
 		mcount = phy_ethtool_get_sset_count(dev->phydev);
@@ -253,7 +240,6 @@ static void dsa_conduit_get_strings(struct net_device *dev, u32 stringset,
 			mcount = 0;
 		ops->get_strings(dev, stringset, data);
 	}
-	netdev_unlock_ops(dev);
 
 	list_for_each_entry(dp, &dst->ports, list) {
 		if (!dsa_port_is_dsa(dp) && !dsa_port_is_cpu(dp))
-- 
2.52.0