net: allow netdev_all_upper_get_next_dev_rcu with rtnl lock held

It is useful to be able to walk all upper devices when bringing
a device online where the RTNL lock is held. In this case it
is safe to walk the all_adj_list because the RTNL lock is used
to protect the write side as well.

This patch adds a check to see if the rtnl lock is held before
throwing a warning in netdev_all_upper_get_next_dev_rcu().

Also because we now have a call site for lockdep_rtnl_is_held()
outside COFIG_LOCK_PROVING an inline definition returning 1 is
needed. Similar to the rcu_read_lock_is_held().

Fixes: 2a47fa45d4df ("ixgbe: enable l2 forwarding acceleration for macvlans")
CC: Veaceslav Falico <[e-mail]>
Reported-by: Yuanhan Liu <[e-mail]>
Signed-off-by: John Fastabend <[e-mail]>
Tested-by: Phil Schmitt <[e-mail]>
Signed-off-by: Jeff Kirsher <[e-mail]>

include/linux/rtnetlink.h

···
 extern int rtnl_is_locked(void);
 #ifdef CONFIG_PROVE_LOCKING
 extern int lockdep_rtnl_is_held(void);
+#else
+static inline int lockdep_rtnl_is_held(void)
+{
+	return 1;
+}
 #endif /* #ifdef CONFIG_PROVE_LOCKING */
 
 /**

net/core/dev.c

···
 {
 	struct netdev_adjacent *upper;
 
-	WARN_ON_ONCE(!rcu_read_lock_held());
+	WARN_ON_ONCE(!rcu_read_lock_held() && !lockdep_rtnl_is_held());
 
 	upper = list_entry_rcu((*iter)->next, struct netdev_adjacent, list);