bonding: use rcu_dereference() to access curr_active_slave

The bond_info_show_master already in RCU read-side critical section,
and the we access curr_active_slave without the curr_slave_lock, we
could not sure whether the curr_active_slave will be changed during
the processing, so use RCU to protected the pointer.

Cc: Jay Vosburgh <fubar@us.ibm.com>
Cc: Veaceslav Falico <vfalico@redhat.com>
Cc: Andy Gospodarek <andy@greyhouse.net>
Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_procfs.c

@@ -69,9 +69,7 @@ static void bond_info_show_master(struct seq_file *seq)
 	struct slave *curr;
 	int i;
 
-	read_lock(&bond->curr_slave_lock);
-	curr = bond->curr_active_slave;
-	read_unlock(&bond->curr_slave_lock);
+	curr = rcu_dereference(bond->curr_active_slave);
 
 	seq_printf(seq, "Bonding Mode: %s",
 		   bond_mode_name(bond->params.mode));