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

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Date:	Thu, 24 Sep 2015 23:15:41 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Andrew Lunn <andrew@...n.ch>
Cc:	Florian Fainelli <f.fainelli@...il.com>,
	David Miller <davem@...emloft.net>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	devicetree@...r.kernel.org, Sunil Goutham <sgoutham@...ium.com>,
	Robert Richter <rric@...nel.org>,
	Frank Rowand <frowand.list@...il.com>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	Rob Herring <robh+dt@...nel.org>,
	Michal Simek <michal.simek@...inx.com>, netdev@...r.kernel.org,
	Soren Brinkmann <soren.brinkmann@...inx.com>,
	Iyappan Subramanian <isubramanian@....com>,
	Grant Likely <grant.likely@...aro.org>,
	Li Yang <leoli@...escale.com>,
	Keyur Chudgar <kchudgar@....com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 0/9] Phy, mdiobus, and netdev struct device fixes

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@...n.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.
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