On Tue, Jan 7, 2020 at 3:31 AM Taehee Yoo [off-list ref] wrote:

After "ip link set team0 master team1", the "team1 -> team0" locking path
will be recorded in lockdep key of both team1 and team0.
Then, if "ip link set team1 master team0" is executed, "team0 -> team1"
locking path also will be recorded in lockdep key. At this moment,
lockdep will catch possible deadlock situation and it prints the above
warning message. But, both "team0 -> team1" and "team1 -> team0"
will not be existing concurrently. so the above message is actually wrong.
In order to avoid this message, a recorded locking path should be
removed. So, both lockdep_unregister_key() and lockdep_register_key()
are needed.

So, after you move the key down to each netdevice, they are now treated
as different locks. Is this stacked device scenario the reason why you
move it to per-netdevice? If so, I wonder why not just use nested locks?
Like:

netif_addr_nested_lock(upper, 0);
netif_addr_nested_lock(lower, 1);
netif_addr_nested_unlock(lower);
netif_addr_nested_unlock(upper);

For this case, they could still share a same key.

Thanks for the details!