linux-kernel - Re: [PATCH net] net: dsa: Do not leave DSA master with NULL netdev

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Message-ID: <b32f205a-6ff3-e1db-33d1-6518091f90b4@gmail.com>
Date:   Mon, 4 May 2020 13:40:32 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     netdev <netdev@...r.kernel.org>, allen.pais@...cle.com,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] net: dsa: Do not leave DSA master with NULL
 netdev_ops



On 5/4/2020 1:34 PM, Vladimir Oltean wrote:
> Hi Florian,
> 
> On Mon, 4 May 2020 at 23:19, Florian Fainelli <f.fainelli@...il.com> wrote:
>>
>> When ndo_get_phys_port_name() for the CPU port was added we introduced
>> an early check for when the DSA master network device in
>> dsa_master_ndo_setup() already implements ndo_get_phys_port_name(). When
>> we perform the teardown operation in dsa_master_ndo_teardown() we would
>> not be checking that cpu_dp->orig_ndo_ops was successfully allocated and
>> non-NULL initialized.
>>
>> With network device drivers such as virtio_net, this leads to a NPD as
>> soon as the DSA switch hanging off of it gets torn down because we are
>> now assigning the virtio_net device's netdev_ops a NULL pointer.
>>
>> Fixes: da7b9e9b00d4 ("net: dsa: Add ndo_get_phys_port_name() for CPU port")
>> Reported-by: Allen Pais <allen.pais@...cle.com>
>> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
>> ---
> 
> The fix makes complete sense.
> But on another note, if we don't overlay an ndo_get_phys_port_name if
> the master already has one, doesn't that render the entire mechanism
> of having a reliable way for user space to determine the CPU port
> number pointless?

For the CPU port I would consider ndo_get_phys_port_name() to be more
best effort than an absolute need unlike the user facing ports, where
this is necessary for a variety of actions (e.g.: determining
queues/port numbers etc.) which is why there was no overlay being done
in that case. There is not a good way to cascade the information other
than do something like pX.Y and defining what the X and Y are, what do
you think?
-- 
Florian