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

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Date:   Fri, 22 Jan 2021 14:36:08 +0100
From:   Rasmus Villemoes <rasmus.villemoes@...vas.dk>
To:     Horatiu Vultur <horatiu.vultur@...rochip.com>
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

On 22/01/2021 10.05, Horatiu Vultur wrote:
> 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'.

Hm, you're right, but the underlying problem is the same:
br_mrp_switchdev_set_ring_role() (whose return value is what is used to
determine ->ing_role_offloaded) and br_mrp_switchdev_send_ring_test()
both make use of switchdev_port_obj_add(SWITCHDEV_OBJ_ID_*MRP), and that
function is currently unable to return -EOPNOTSUPP, which it must in
order for the MRP logic to work.

Rasmus