netdev - Re: [PATCH resend net] net: switchdev: don't set port_obj

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Date:   Fri, 22 Jan 2021 10:05:05 +0100
From:   Horatiu Vultur <horatiu.vultur@...rochip.com>
To:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>
CC:     <netdev@...r.kernel.org>, Jiri Pirko <jiri@...lanox.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Petr Machata <petrm@...lanox.com>,
        Ido Schimmel <idosch@...lanox.com>,
        "David S . Miller" <davem@...emloft.net>,
        Ivan Vecera <ivecera@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH resend net] net: switchdev: don't set
 port_obj_info->handled true when -EOPNOTSUPP

The 01/22/2021 00:43, Rasmus Villemoes wrote:
> 
> It's not true that switchdev_port_obj_notify() only inspects the
> ->handled field of "struct switchdev_notifier_port_obj_info" if
> call_switchdev_blocking_notifiers() returns 0 - there's a WARN_ON()
> triggering for a non-zero return combined with ->handled not being
> true. But the real problem here is that -EOPNOTSUPP is not being
> properly handled.
> 
> The wrapper functions switchdev_handle_port_obj_add() et al change a
> return value of -EOPNOTSUPP to 0, and the treatment of ->handled in
> switchdev_port_obj_notify() seems to be designed to change that back
> to -EOPNOTSUPP in case nobody actually acted on the notifier (i.e.,
> everybody returned -EOPNOTSUPP).
> 
> Currently, as soon as some device down the stack passes the check_cb()
> check, ->handled gets set to true, which means that
> switchdev_port_obj_notify() cannot actually ever return -EOPNOTSUPP.
> 
> This, for example, means that the detection of hardware offload
> support in the MRP code is broken - br_mrp_set_ring_role() always ends
> up setting mrp->ring_role_offloaded to 1, despite not a single
> mainline driver implementing any of the SWITCHDEV_OBJ_ID*_MRP. So
> since the MRP code thinks the generation of MRP test frames has been
> offloaded, no such frames are actually put on the wire.

Just a small correction to what you have said regarding MRP. Is not the
option mrp->ring_role_offload that determines if the MRP Test frames are
generated by the HW but is the return value of the function
'br_mrp_switchdev_send_ring_test' called from function
'br_mrp_start_test'. But everything else looks good.

I have also started to work on a patch series where I try to improve the
way the return values of switchdev calls are handled in MRP. I should be
able to send these patches by the end of week.

> 
> So, continue to set ->handled true if any callback returns success or
> any error distinct from -EOPNOTSUPP. But if all the callbacks return
> -EOPNOTSUPP, make sure that ->handled stays false, so the logic in
> switchdev_port_obj_notify() can propagate that information.
> 
> Fixes: f30f0601eb93 ("switchdev: Add helpers to aid traversal through lower devices")
> Signed-off-by: Rasmus Villemoes <rasmus.villemoes@...vas.dk>
> ---
> Resending with more folks on cc and a tentative fixes tag.
> 
>  net/switchdev/switchdev.c | 23 +++++++++++++----------
>  1 file changed, 13 insertions(+), 10 deletions(-)
> 
> diff --git a/net/switchdev/switchdev.c b/net/switchdev/switchdev.c
> index 23d868545362..2c1ffc9ba2eb 100644
> --- a/net/switchdev/switchdev.c
> +++ b/net/switchdev/switchdev.c
> @@ -460,10 +460,11 @@ static int __switchdev_handle_port_obj_add(struct net_device *dev,
>         extack = switchdev_notifier_info_to_extack(&port_obj_info->info);
> 
>         if (check_cb(dev)) {
> -               /* This flag is only checked if the return value is success. */
> -               port_obj_info->handled = true;
> -               return add_cb(dev, port_obj_info->obj, port_obj_info->trans,
> -                             extack);
> +               err = add_cb(dev, port_obj_info->obj, port_obj_info->trans,
> +                            extack);
> +               if (err != -EOPNOTSUPP)
> +                       port_obj_info->handled = true;
> +               return err;
>         }
> 
>         /* Switch ports might be stacked under e.g. a LAG. Ignore the
> @@ -515,9 +516,10 @@ static int __switchdev_handle_port_obj_del(struct net_device *dev,
>         int err = -EOPNOTSUPP;
> 
>         if (check_cb(dev)) {
> -               /* This flag is only checked if the return value is success. */
> -               port_obj_info->handled = true;
> -               return del_cb(dev, port_obj_info->obj);
> +               err = del_cb(dev, port_obj_info->obj);
> +               if (err != -EOPNOTSUPP)
> +                       port_obj_info->handled = true;
> +               return err;
>         }
> 
>         /* Switch ports might be stacked under e.g. a LAG. Ignore the
> @@ -568,9 +570,10 @@ static int __switchdev_handle_port_attr_set(struct net_device *dev,
>         int err = -EOPNOTSUPP;
> 
>         if (check_cb(dev)) {
> -               port_attr_info->handled = true;
> -               return set_cb(dev, port_attr_info->attr,
> -                             port_attr_info->trans);
> +               err = set_cb(dev, port_attr_info->attr, port_attr_info->trans);
> +               if (err != -EOPNOTSUPP)
> +                       port_attr_info->handled = true;
> +               return err;
>         }
> 
>         /* Switch ports might be stacked under e.g. a LAG. Ignore the
> --
> 2.23.0
> 

-- 
/Horatiu