bonding: no longer use RTNL in bonding_show_bonds()

netdev structures are already RCU protected.

Change bond_init() and bond_uninit() to use RCU
enabled list_add_tail_rcu() and list_del_rcu().

Then bonding_show_bonds() can use rcu_read_lock()
while iterating through bn->dev_list.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Jay Vosburgh <jay.vosburgh@canonical.com>
Link: https://lore.kernel.org/r/20240408190437.2214473-2-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/bonding/bond_main.c

@@ -5933,7 +5933,7 @@ static void bond_uninit(struct net_device *bond_dev)
 
 	bond_set_slave_arr(bond, NULL, NULL);
 
-	list_del(&bond->bond_list);
+	list_del_rcu(&bond->bond_list);
 
 	bond_debug_unregister(bond);
 }
@@ -6347,7 +6347,7 @@ static int bond_init(struct net_device *bond_dev)
 	spin_lock_init(&bond->stats_lock);
 	netdev_lockdep_set_classes(bond_dev);
 
-	list_add_tail(&bond->bond_list, &bn->dev_list);
+	list_add_tail_rcu(&bond->bond_list, &bn->dev_list);
 
 	bond_prepare_sysfs_group(bond);
 

drivers/net/bonding/bond_sysfs.c

@@ -37,12 +37,12 @@ static ssize_t bonding_show_bonds(const struct class *cls,
 {
 	const struct bond_net *bn =
 		container_of_const(attr, struct bond_net, class_attr_bonding_masters);
-	int res = 0;
 	struct bonding *bond;
+	int res = 0;
 
-	rtnl_lock();
+	rcu_read_lock();
 
-	list_for_each_entry(bond, &bn->dev_list, bond_list) {
+	list_for_each_entry_rcu(bond, &bn->dev_list, bond_list) {
 		if (res > (PAGE_SIZE - IFNAMSIZ)) {
 			/* not enough space for another interface name */
 			if ((PAGE_SIZE - res) > 10)
@@ -55,7 +55,7 @@ static ssize_t bonding_show_bonds(const struct class *cls,
 	if (res)
 		buf[res-1] = '\n'; /* eat the leftover space */
 
-	rtnl_unlock();
+	rcu_read_unlock();
 	return res;
 }