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

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Message-ID: <20210123124425.324b8a94@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Sat, 23 Jan 2021 12:44:25 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>
Cc:     Horatiu Vultur <horatiu.vultur@...rochip.com>,
        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>
Subject: Re: [PATCH resend net] net: switchdev: don't set
 port_obj_info->handled true when -EOPNOTSUPP

On Fri, 22 Jan 2021 14:36:08 +0100 Rasmus Villemoes wrote:
> 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.

Could you reword the commit message to avoid confusion for folks
reading git history and repost? You can keep Petr's tag.