netdev - Re: PROBLEM: (DSA/Microchip): 802.1Q-Header lost on KSZ9477-DSA ingress without bridge

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Message-ID: <20200804192933.pe32dhfkrlspdhot@skbuf>
Date:   Tue, 4 Aug 2020 22:29:33 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "Gaube, Marvin (THSE-TL1)" <Marvin.Gaube@...at.de>,
        Florian Fainelli <f.fainelli@...il.com>,
        Woojung Huh <woojung.huh@...rochip.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: PROBLEM: (DSA/Microchip): 802.1Q-Header lost on KSZ9477-DSA
 ingress without bridge

On Tue, Aug 04, 2020 at 07:54:18AM -0700, Eric Dumazet wrote:
> 
> My 2013 commit was a bug fix, and hinted that in the future (eg in
> net-next tree) the stop-the-bleed could be refined.
> 
> +               /* Note: we might in the future use prio bits
> +                * and set skb->priority like in vlan_do_receive()
> +                * For the time being, just ignore Priority Code Point
> +                */
> +               skb->vlan_tci = 0;
> 
> If you believe this can be done, this is great.

Do you have a reproducer for that bug? I am willing to spend some time
understand what is going on. This has nothing to do with priority. You
vaguely described a problem with 802.1p (VLAN 0) and used that as an
excuse to clear the entire vlan hwaccel tag regardless of VLAN ID. I'm
curious because we also now have commit 36b2f61a42c2 ("net: handle
802.1P vlan 0 packets properly") in that general area, and I simply want
to know if your patch still serves a valid purpose or not.

Thanks,
-Vladimir