Re: [PATCH] net: dsa: drop some VLAs in switch.c

[Andrew Lunn <andrew@lunn.ch>]

> > You could make the bitmap part of the dsa_switch structure. This is
> > allocated by dsa_switch_alloc() and is passed the number of ports.
> > Doing the allocation there means you don't need to worry about it
> > failing in dsa_switch_mdb_add() or dsa_switch_vlan_add().
> 
> Are dsa_switch_mdb_add() and dsa_switch_vlan_add() guaranteed to be
> single-threaded?

Yes, that is the interesting question here.... against each other, or
themselves?

They are called from a notifier chain. It is the same notifier chain
for both dsa_switch_mdb_add() and dsa_switch_vlan_add().

notifier_call_chain() itself appears to not provide any guarantees
about the same handler being called in parallel.

It is dsa_port_notify() which is calling the notifier_call_chain().
This is being called by both dsa_port_vlan_add() and
dsa_port_mdb_add() in dsa_slave_port_obj_add(). This is a switchdev
op. switchdev_port_obj_add_now() does have ASSERT_RTNL(); So that
should serialize everything.

     Andrew