netdev - Re: [RFC net] net: dsa: Add missing reference counting

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Message-ID: <20200507130251.GL208718@lunn.ch>
Date:   Thu, 7 May 2020 15:02:51 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Vivien Didelot <vivien.didelot@...il.com>, netdev@...r.kernel.org,
        olteanv@...il.com, "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC net] net: dsa: Add missing reference counting

On Wed, May 06, 2020 at 02:24:14PM -0700, Florian Fainelli wrote:
> 
> 
> On 5/5/2020 2:23 PM, Vivien Didelot wrote:
> > On Tue,  5 May 2020 14:02:53 -0700, Florian Fainelli <f.fainelli@...il.com> wrote:
> >> If we are probed through platform_data we would be intentionally
> >> dropping the reference count on master after dev_to_net_device()
> >> incremented it. If we are probed through Device Tree,
> >> of_find_net_device() does not do a dev_hold() at all.
> >>
> >> Ensure that the DSA master device is properly reference counted by
> >> holding it as soon as the CPU port is successfully initialized and later
> >> released during dsa_switch_release_ports(). dsa_get_tag_protocol() does
> >> a short de-reference, so we hold and release the master at that time,
> >> too.
> >>
> >> Fixes: 83c0afaec7b7 ("net: dsa: Add new binding implementation")
> >> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> > 
> > Reviewed-by: Vivien Didelot <vivien.didelot@...il.com>
> > 
> Andrew, Vladimir, any thoughts on that?

Hi Florian

Have you looked at how other stacked drivers do this? bond/team, vlan,
bridge, BATMAN?

Do we maybe need to subscribe to the master devices notifier chain,
and do a tear down when the device is removed?

    Andrew