netdev - Re: [RFC PATCH net] net: dsa: flush switchdev workqueue before tearing down CPU/DSA ports

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Date:   Sun, 12 Sep 2021 19:06:25 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Vladimir Oltean <vladimir.oltean@....com>, netdev@...r.kernel.org,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [RFC PATCH net] net: dsa: flush switchdev workqueue before
 tearing down CPU/DSA ports



On 9/12/2021 9:33 AM, Vladimir Oltean wrote:
> On Sun, Sep 12, 2021 at 09:24:53AM -0700, Florian Fainelli wrote:
>>
>>
>> On 9/12/2021 9:19 AM, Vladimir Oltean wrote:
>>> On Sun, Sep 12, 2021 at 09:13:36AM -0700, Florian Fainelli wrote:
>>>> Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
>>>>
>>>> Did you post this as a RFC for a particular reason, or just to give
>>>> reviewers some time?
>>>
>>> Both.
>>>
>>> In principle there's nothing wrong with what this patch does, only
>>> perhaps maybe something with what it doesn't do.
>>>
>>> We keep saying that a network interface should be ready to pass traffic
>>> as soon as it's registered, but that "walk dst->ports linearly when
>>> calling dsa_port_setup" might not really live up to that promise.
>>
>> That promise most definitively existed back when Lennert wrote this code and
>> we had an array of ports and the switch drivers brought up their port in
>> their ->setup() method, nowadays, not so sure anymore because of the
>> .port_enable() as much as the list.
>>
>> This is making me wonder whether the occasional messages I am seeing on
>> system suspend from __dev_queue_xmit: Virtual device %s asks to queue
>> packet! might have something to do with that and/or the inappropriate
>> ordering between suspending the switch and the DSA master.
> 
> Sorry, I have never tested the suspend/resume code path, mostly because
> I don't know what would the easiest way be to wake up my systems from
> suspend. If you could give me some pointers there I would be glad to
> look into it.

If your systems support suspend/resume just do:

echo mem > /sys/power/state
or
echo standby > /sys/power/state

if they don't, then maybe a x86 VM with dsa_loop may precipitate the 
problem, but since it uses DSA_TAG_PROTO_NONE, I doubt it, we would need 
to pass traffic on the DSA devices for this warning to show up.
-- 
Florian