On 4/30/2024 12:27 PM, Joseph Huang wrote:

On 4/29/2024 8:59 PM, Vladimir Oltean wrote:

quoted

On Mon, Apr 29, 2024 at 06:07:25PM -0400, Joseph Huang wrote:

quoted

Something like this (some layers omitted for brevity)?

                                       +br_iterator
                                       |  for each mdb
                                       |    _br_switchdev_mdb_notify
 rtnl_lock                             |      without F_DEFER flag
  |                                    |      |
  +switchdev_port_attr_set_deferred    |      +switchdev_port_obj_notify
    |                                  |        |
    +dsa_port_mrouter                  |        +dsa_user_port_obj_a/d
      |                                |          |
      +mv88e6xxx_port_mrouter----------+          
+mv88e6xxx_port_obj_a/d
                                         |
  +--------------------------------------+
  |
rtnl_unlock

At a _very_ superficial glance, I don't think you are properly
accounting for the fact that even with rtnl_lock() held, there are still
SWITCHDEV_OBJ_ID_PORT_MDB events which may be pending on the switchdev
chain. Without a switchdev_deferred_process() flush call, you won't be
getting rid of them, so when you rtnl_unlock(), they will still run.

Even worse, holding rtnl_lock() will not stop the bridge multicast layer
from modifying its br->mdb_list; only br->multicast_lock will.

So you may be better off also acquiring br->multicast_lock, and
notifying the MDB entries to the switchdev chain _with_the F_DEFER flag.

Like this?

                                       +br_iterator(dsa_cb)
                                       |  lock br->multicask_lock
                                       |  for each mdb
                                       |    br_switchdev_mdb_notify
 rtnl_lock                             |      |
  |                                    |      +switchdev_port_obj_._defer
  +switchdev_port_attr_set_deferred    |  unlock br->multicast_lock
    |                                  |
    +dsa_port_mrouter                  |
      |                                |
      +mv88e6xxx_port_mrouter----------+
                                         |
  +--------------------------------------+
  |
rtnl_unlock

(potential task change)

rtnl_lock
  |
  +switchdev_deferred_process
  | flush all queued dfitems in queuing order
  |
rtnl_unlock

I'm not that familiar with the bridge code, but is there any concern 
with potential deadlock here (between rtnl_lock and br->multicast_lock)?

Hi Nik,

Do you know if it's safe to acquire rtnl_lock and br->multicast_lock in 
the following sequence? Is there any potential possibility for a deadlock?

rtnl_lock
spin_lock(br->multicast_lock)
spin_unlock(br->multicast_lock)
rtnl_unlock

If the operation is safe, the next question is should it be spin_lock or 
spin_lock_bh?

Thanks,
Joseph