bonding: remove bond read lock for bond_loadbalance_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 add 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 0a7e3257854006d650cdb5990918c720abd85fc4..a620dfae1c822e77749f96718f502a9a2c07fe12 100644 (file)
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -2396,10 +2396,13 @@ void bond_loadbalance_arp_mon(struct work_struct *work)
        struct list_head *iter;
        int do_failover = 0;
 
-       read_lock(&bond->lock);
+       if (!rtnl_trylock())
+               goto re_arm;
 
-       if (!bond_has_slaves(bond))
+       if (!bond_has_slaves(bond)) {
+               rtnl_unlock();
                goto re_arm;
+       }
 
        oldcurrent = bond->curr_active_slave;
        /* see if any of the previous devices are up now (i.e. they have
@@ -2481,13 +2484,12 @@ void bond_loadbalance_arp_mon(struct work_struct *work)
                write_unlock_bh(&bond->curr_slave_lock);
                unblock_netpoll_tx();
        }
+       rtnl_unlock();
 
 re_arm:
        if (bond->params.arp_interval)
                queue_delayed_work(bond->wq, &bond->arp_work,
                                   msecs_to_jiffies(bond->params.arp_interval));
-
-       read_unlock(&bond->lock);
 }
 
 /*