bonding: remove bond read lock for bond_activebackup_arp_mon()

The bond slave list may change when the monitor is running, the slave list is no longer
protected by bond->lock, only protected by rtnl lock(), so we have 3 ways to modify it:
1.add bond_master_upper_dev_link() and bond_upper_dev_unlink() in bond->lock, but it is unsafe
to call call_netdevice_notifiers() in write lock.
2.remove unused bond->lock for monitor function, only use the existing rtnl lock().
3.use rcu_read_lock() to protect it, of course, it will transform bond_for_each_slave to
bond_for_each_slave_rcu() and performance is better, but in slow path, it is ignored.
so I remove the bond->lock and move the rtnl lock to protect the whole monitor function.

Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index a620dfae1c822e77749f96718f502a9a2c07fe12..535570ea8bbc98e8090d189a81f58327eca2cae1 100644 (file)
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -2726,51 +2726,31 @@ void bond_activebackup_arp_mon(struct work_struct *work)
        struct bonding *bond = container_of(work, struct bonding,
                                            arp_work.work);
        bool should_notify_peers = false;
-       int delta_in_ticks;
 
-       read_lock(&bond->lock);
-
-       delta_in_ticks = msecs_to_jiffies(bond->params.arp_interval);
+       if (!rtnl_trylock())
+               goto re_arm;
 
-       if (!bond_has_slaves(bond))
+       if (!bond_has_slaves(bond)) {
+               rtnl_unlock();
                goto re_arm;
+       }
 
        should_notify_peers = bond_should_notify_peers(bond);
 
-       if (bond_ab_arp_inspect(bond)) {
-               read_unlock(&bond->lock);
-
-               /* Race avoidance with bond_close flush of workqueue */
-               if (!rtnl_trylock()) {
-                       read_lock(&bond->lock);
-                       delta_in_ticks = 1;
-                       should_notify_peers = false;
-                       goto re_arm;
-               }
-
-               read_lock(&bond->lock);
-
+       if (bond_ab_arp_inspect(bond))
                bond_ab_arp_commit(bond);
 
-               read_unlock(&bond->lock);
-               rtnl_unlock();
-               read_lock(&bond->lock);
-       }
-
        bond_ab_arp_probe(bond);
 
-re_arm:
-       if (bond->params.arp_interval)
-               queue_delayed_work(bond->wq, &bond->arp_work, delta_in_ticks);
+       if (should_notify_peers)
+               call_netdevice_notifiers(NETDEV_NOTIFY_PEERS, bond->dev);
 
-       read_unlock(&bond->lock);
+       rtnl_unlock();
 
-       if (should_notify_peers) {
-               if (!rtnl_trylock())
-                       return;
-               call_netdevice_notifiers(NETDEV_NOTIFY_PEERS, bond->dev);
-               rtnl_unlock();
-       }
+re_arm:
+       if (bond->params.arp_interval)
+               queue_delayed_work(bond->wq, &bond->arp_work,
+                               msecs_to_jiffies(bond->params.arp_interval));
 }
 
 /*-------------------------- netdev event handling --------------------------*/