net: dsa: replay master state events in dsa_tree_{setup,teardown}_master

net: dsa: replay master state events in dsa_tree_{setup,teardown}_master

In order for switch driver to be able to make simple and reliable use of
the master tracking operations, they must also be notified of the
initial state of the DSA master, not just of the changes. This is
because they might enable certain features only during the time when
they know that the DSA master is up and running.

Therefore, this change explicitly checks the state of the DSA master
under the same rtnl_mutex as we were holding during the
dsa_master_setup() and dsa_master_teardown() call. The idea being that
if the DSA master became operational in between the moment in which it
became a DSA master (dsa_master_setup set dev->dsa_ptr) and the moment
when we checked for the master being up, there is a chance that we
would emit a ->master_state_change() call with no actual state change.
We need to avoid that by serializing the concurrent netdevice event with
us. If the netdevice event started before, we force it to finish before
we begin, because we take rtnl_lock before making netdev_uses_dsa()
return true. So we also handle that early event and do nothing on it.
Similarly, if the dev_open() attempt is concurrent with us, it will
attempt to take the rtnl_mutex, but we're holding it. We'll see that
the master flag IFF_UP isn't set, then when we release the rtnl_mutex
we'll process the NETDEV_UP notifier.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>