On Thu, Sep 24, 2015 at 11:57:31PM +0200, Andrew Lunn wrote:

Hi Russell

I tested both of these with my board. It is a Freescale Vybrid, using
the FEC ethernet driver, and i have three switches attached, using
mdio-mux to give three mdio busses.

No obvious regressions, my board boots, the switches are all present
and correct. I built the FEC driver as a module, and it won't unload:

 kernel:unregister_netdevice: waiting for eth1 to become free. Usage count = 1
unregister_netdevice: waiting for eth1 to become free. Usage count = 1

i assume because DSA holds a reference. I've not tried a fully module
build, DSA has issues with that.

Tested-by: Andrew Lunn <andrew@lunn.ch>

Thanks for testing.  Please could you confirm whether the same behaviour
is observed without the patches, just to make absolutely sure that isn't
a regression.

However, I think you are correct - I'm unable to locate where in the
DSA code:
- dst->master_dev's dev_hold() is undone (hence a reference left)
- dst is freed - dsa_probe() allocates it using kzalloc(), but
  dsa_remove() and it's children don't free this structure.

There's no notifier which detects whether the underlying device has
gone away - it registers a netdev notifier (dsa_slave_netdevice_event)
but this only deals with slave devices, not the master device.

Thanks.

-- 
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.