bonding: 3ad: Fix the conflict between bond_update_slave_arr and the state machine

The bond works in mode 4, and performs down/up operations on the bond
that is normally negotiated. The probability of bond-> slave_arr is NULL

Test commands:
   ifconfig bond1 down
   ifconfig bond1 up

The conflict occurs in the following process：

__dev_open (CPU A)
--bond_open
  --queue_delayed_work(bond->wq,&bond->ad_work,0);
  --bond_update_slave_arr
    --bond_3ad_get_active_agg_info

ad_work(CPU B)
--bond_3ad_state_machine_handler
  --ad_agg_selection_logic

ad_work runs on cpu B. In the function ad_agg_selection_logic, all
agg->is_active will be cleared. Before the new active aggregator is
selected on CPU B, bond_3ad_get_active_agg_info failed on CPU A,
bond->slave_arr will be set to NULL. The best aggregator in
ad_agg_selection_logic has not changed, no need to update slave arr.

The conflict occurred in that ad_agg_selection_logic clears
agg->is_active under mode_lock, but bond_open -> bond_update_slave_arr
is inspecting agg->is_active outside the lock.

Also, bond_update_slave_arr is normal for potential sleep when
allocating memory, so replace the WARN_ON with a call to might_sleep.
Signed-off-by: Njinyiting <jinyiting@huawei.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_main.c

@@ -4391,9 +4391,7 @@ int bond_update_slave_arr(struct bonding *bond, struct slave *skipslave)
 	int agg_id = 0;
 	int ret = 0;
 
-#ifdef CONFIG_LOCKDEP
-	WARN_ON(lockdep_is_held(&bond->mode_lock));
-#endif
+	might_sleep();
 
 	usable_slaves = kzalloc(struct_size(usable_slaves, arr,
 					    bond->slave_cnt), GFP_KERNEL);
@@ -4406,7 +4404,9 @@ int bond_update_slave_arr(struct bonding *bond, struct slave *skipslave)
 	if (BOND_MODE(bond) == BOND_MODE_8023AD) {
 		struct ad_info ad_info;
 
+		spin_lock_bh(&bond->mode_lock);
 		if (bond_3ad_get_active_agg_info(bond, &ad_info)) {
+			spin_unlock_bh(&bond->mode_lock);
 			pr_debug("bond_3ad_get_active_agg_info failed\n");
 			/* No active aggragator means it's not safe to use
 			 * the previous array.
@@ -4414,6 +4414,7 @@ int bond_update_slave_arr(struct bonding *bond, struct slave *skipslave)
 			bond_reset_slave_arr(bond);
 			goto out;
 		}
+		spin_unlock_bh(&bond->mode_lock);
 		agg_id = ad_info.aggregator_id;
 	}
 	bond_for_each_slave(bond, slave, iter) {