linux-kernel - Re: [PATCH] Revert "net: linkwatch: add check for netdevice being present to linkwatch_do

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Date:   Mon, 14 Sep 2020 09:40:12 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     David Miller <davem@...emloft.net>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>, Jakub Kicinski <kuba@...nel.org>,
        Gaku Inami <gaku.inami.xh@...esas.com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        netdev <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <nikolay@...dia.com>,
        bridge@...ts.linux-foundation.org
Subject: Re: [PATCH] Revert "net: linkwatch: add check for netdevice being
 present to linkwatch_do_dev"

Hi David,

CC bridge

On Sun, Sep 13, 2020 at 3:34 AM David Miller <davem@...emloft.net> wrote:
> From: Geert Uytterhoeven <geert@...ux-m68k.org>
> Date: Sat, 12 Sep 2020 14:33:59 +0200
>
> > "dev" is not the bridge device, but the physical Ethernet interface, which
> > may already be suspended during s2ram.
>
> Hmmm, ok.
>
> Looking more deeply NETDEV_CHANGE causes br_port_carrier_check() to run which
> exits early if netif_running() is false, which is going to be true if
> netif_device_present() is false:
>
>         *notified = false;
>         if (!netif_running(br->dev))
>                 return;
>
> The only other work the bridge notifier does is:
>
>         if (event != NETDEV_UNREGISTER)
>                 br_vlan_port_event(p, event);
>
> and:
>
>         /* Events that may cause spanning tree to refresh */
>         if (!notified && (event == NETDEV_CHANGEADDR || event == NETDEV_UP ||
>                           event == NETDEV_CHANGE || event == NETDEV_DOWN))
>                 br_ifinfo_notify(RTM_NEWLINK, NULL, p);
>
> So some vlan stuff, and emitting a netlink message to any available
> listeners.
>
> Should we really do all of this for a device which is not even
> present?
>
> This whole situation seems completely illogical.  The device is
> useless, it logically has no link or other state that can be managed
> or used, while it is not present.
>
> So all of these bridge operations should only happen when the device
> transitions back to present again.

Thanks for your analysis!
I'd like to defer this to the bridge people (CC).

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds