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

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Date:   Mon, 13 Sep 2021 05:12:35 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Florian Fainelli <f.fainelli@...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 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?