bonding: use rcu_dereference_rtnl when get bonding active slave

bond_option_active_slave_get_rcu() should not be used in rtnl_mutex as it
use rcu_dereference(). Replace to rcu_dereference_rtnl() so we also can use
this function in rtnl protected context.

With this update, we can rmeove the rcu_read_lock/unlock in
bonding .ndo_eth_ioctl and .get_ts_info.

Reported-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Fixes: 94dd016 ("bond: pass get_ts_info and SIOC[SG]HWTSTAMP ioctl to active device")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: liuhangbin

drivers/net/bonding/bond_main.c

@@ -4133,9 +4133,7 @@ static int bond_eth_ioctl(struct net_device *bond_dev, struct ifreq *ifr, int cm
 
 		fallthrough;
 	case SIOCGHWTSTAMP:
-		rcu_read_lock();
 		real_dev = bond_option_active_slave_get_rcu(bond);
-		rcu_read_unlock();
 		if (!real_dev)
 			return -EOPNOTSUPP;
 
@@ -5382,9 +5380,7 @@ static int bond_ethtool_get_ts_info(struct net_device *bond_dev,
 	struct net_device *real_dev;
 	struct phy_device *phydev;
 
-	rcu_read_lock();
 	real_dev = bond_option_active_slave_get_rcu(bond);
-	rcu_read_unlock();
 	if (real_dev) {
 		ops = real_dev->ethtool_ops;
 		phydev = real_dev->phydev;

include/net/bonding.h

@@ -346,7 +346,7 @@ static inline bool bond_uses_primary(struct bonding *bond)
 
 static inline struct net_device *bond_option_active_slave_get_rcu(struct bonding *bond)
 {
-	struct slave *slave = rcu_dereference(bond->curr_active_slave);
+	struct slave *slave = rcu_dereference_rtnl(bond->curr_active_slave);
 
 	return bond_uses_primary(bond) && slave ? slave->dev : NULL;
 }