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 19:20:23 -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 7:12 PM, Vladimir Oltean wrote:
> On Sun, Sep 12, 2021 at 07:06:25PM -0700, Florian Fainelli wrote:
>>
>>
>> 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.
> 
> I figured out a working combination in the meanwhile, I even found a bug
> in the process:
> https://patchwork.kernel.org/project/netdevbpf/patch/20210912192805.1394305-1-vladimir.oltean@nxp.com/
> 
> However I did not see those messages getting printed while pinging after
> system resume (note that none of the DSA switch drivers I tested with
> did implement .suspend or .resume), with net-next or with linux-stable/linux-5.14.y.
> 
> Is there more to your setup to reproduce this issue?

All switch ports are brought up with a DHCP client, the issue is 
definitively intermittent and not frequent, I don't have suspend/resume 
working on 5.14.y yet, but going as far back as 5.10.y should let you 
see the same kind of messages.
-- 
Florian