netdev - Re: [PATCH net-next] mlx4: make sure to always set the port type

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Message-ID: <20200907071939.GK2997@nanopsycho.orion>
Date:   Mon, 7 Sep 2020 09:19:39 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net,
        netdev@...r.kernel.org, kernel-team@...com, tariqt@...lanox.com,
        yishaih@...lanox.com, linux-rdma@...r.kernel.org
Subject: Re: [PATCH net-next] mlx4: make sure to always set the port type

Mon, Sep 07, 2020 at 08:48:30AM CEST, leon@...nel.org wrote:
>On Mon, Sep 07, 2020 at 08:21:35AM +0200, Jiri Pirko wrote:
>> Sun, Sep 06, 2020 at 06:33:05PM CEST, kuba@...nel.org wrote:
>> >On Sun, 6 Sep 2020 10:27:59 +0300 Leon Romanovsky wrote:
>> >> On Fri, Sep 04, 2020 at 01:06:21PM -0700, Jakub Kicinski wrote:
>> >> > Even tho mlx4_core registers the devlink ports, it's mlx4_en
>> >> > and mlx4_ib which set their type. In situations where one of
>> >> > the two is not built yet the machine has ports of given type
>> >> > we see the devlink warning from devlink_port_type_warn() trigger.
>> >> >
>> >> > Having ports of a type not supported by the kernel may seem
>> >> > surprising, but it does occur in practice - when the unsupported
>> >> > port is not plugged in to a switch anyway users are more than happy
>> >> > not to see it (and potentially allocate any resources to it).
>> >> >
>> >> > Set the type in mlx4_core if type-specific driver is not built.
>> >> >
>> >> > Signed-off-by: Jakub Kicinski <kuba@...nel.org>
>> >> > ---
>> >> >  drivers/net/ethernet/mellanox/mlx4/main.c | 11 +++++++++++
>> >> >  1 file changed, 11 insertions(+)
>> >> >
>> >> > diff --git a/drivers/net/ethernet/mellanox/mlx4/main.c b/drivers/net/ethernet/mellanox/mlx4/main.c
>> >> > index 258c7a96f269..70cf24ba71e4 100644
>> >> > --- a/drivers/net/ethernet/mellanox/mlx4/main.c
>> >> > +++ b/drivers/net/ethernet/mellanox/mlx4/main.c
>> >> > @@ -3031,6 +3031,17 @@ static int mlx4_init_port_info(struct mlx4_dev *dev, int port)
>> >> >  	if (err)
>> >> >  		return err;
>> >> >
>> >> > +	/* Ethernet and IB drivers will normally set the port type,
>> >> > +	 * but if they are not built set the type now to prevent
>> >> > +	 * devlink_port_type_warn() from firing.
>> >> > +	 */
>> >> > +	if (!IS_ENABLED(CONFIG_MLX4_EN) &&
>> >> > +	    dev->caps.port_type[port] == MLX4_PORT_TYPE_ETH)
>> >> > +		devlink_port_type_eth_set(&info->devlink_port, NULL);
>> >>                                                                ^^^^^
>> >>
>> >> Won't it crash in devlink_port_type_eth_set()?
>> >> The first line there dereferences pointer.
>> >>   7612         const struct net_device_ops *ops = netdev->netdev_ops;
>> >
>> >Damn, good catch. It's not supposed to be required. I'll patch devlink.
>>
>> When you set the port type to ethernet, you should have the net_device
>> instance. Why wouldn't you?
>
>It is how mlx4 is implemented, see mlx4_dev_cap() function:
>588         for (i = 1; i <= dev->caps.num_ports; ++i) {
>589                 dev->caps.port_type[i] = MLX4_PORT_TYPE_NONE;
>....
>
>The port type is being set to IB or ETH without relation to net_device,
>fixing it will require very major code rewrite for the stable driver
>that in maintenance mode.

Because the eth driver is not loaded, I see. The purpose of the
WARN in devlink_port_type_eth_set is to prevent drivers from registering
particular port without netdev/ibdev. That is what was repeatedly
happening in the past as the driver developers didn't know they need to
do it or were just lazy to do so.

I wonder if there is any possibility to do both...

>
>>
>>
>> >
>> >> And can we call to devlink_port_type_*_set() without IS_ENABLED() check?
>> >
>> >It'll generate two netlink notifications - not the end of the world but
>> >also doesn't feel super clean.
>
>I would say that such a situation is corner case during the driver init and
>not an end of the world to see double netlink message.
>
>Thanks