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>

1 files changed, 13 insertions, 33 deletions

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index a620dfae1c82..535570ea8bbc 100644
--- 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 --------------------------*/