bonding: do not set usable_slaves for broadcast mode

After commit e0caeb2 ("net: bonding: update the slave array for broadcast mode"),
broadcast mode will also set all_slaves and usable_slaves during
bond_enslave(). But if we also set updelay, during enslave, the
slave init state will be BOND_LINK_BACK. And later
bond_update_slave_arr() will alloc usable_slaves but add nothing.
This will cause bond_miimon_inspect() to have ignore_updelay
always true. So the updelay will be always ignored. e.g.

[    6.498368] bond0: (slave veth2): link status definitely down, disabling slave
[    7.536371] bond0: (slave veth2): link status up, enabling it in 0 ms
[    7.536402] bond0: (slave veth2): link status definitely up, 10000 Mbps full duplex

To fix it, we can either always call bond_update_slave_arr() on every
place when link changes. Or, let's just not set usable_slaves for
broadcast mode.

Fixes: e0caeb2 ("net: bonding: update the slave array for broadcast mode")
Reported-by: Liang Li <[email protected]>
Signed-off-by: Hangbin Liu <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: liuhangbin

drivers/net/bonding/bond_main.c

@@ -5069,13 +5069,18 @@ static void bond_set_slave_arr(struct bonding *bond,
 {
 	struct bond_up_slave *usable, *all;
 
-	usable = rtnl_dereference(bond->usable_slaves);
-	rcu_assign_pointer(bond->usable_slaves, usable_slaves);
-	kfree_rcu(usable, rcu);
-
 	all = rtnl_dereference(bond->all_slaves);
 	rcu_assign_pointer(bond->all_slaves, all_slaves);
 	kfree_rcu(all, rcu);
+
+	if (BOND_MODE(bond) == BOND_MODE_BROADCAST) {
+		kfree_rcu(usable_slaves, rcu);
+		return;
+	}
+
+	usable = rtnl_dereference(bond->usable_slaves);
+	rcu_assign_pointer(bond->usable_slaves, usable_slaves);
+	kfree_rcu(usable, rcu);
 }
 
 static void bond_reset_slave_arr(struct bonding *bond)