Re: [PATCH v3 0/9] Phy, mdiobus, and netdev struct device fixes

From: Russell King - ARM Linux
Date: Thu Sep 24 2015 - 18:16:12 EST

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@xxxxxxx>

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.


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