netdev - RE: [PATCH] net: openvswitch: fix race on port output

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Date:   Tue, 4 Apr 2023 07:25:32 +0000
From:   Felix Hüttner <felix.huettner@...l.schwarz>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "dev@...nvswitch.org" <dev@...nvswitch.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Luca Czesla <Luca.Czesla@...l.schwarz>
Subject: RE: [PATCH] net: openvswitch: fix race on port output

On Mon, 3 Apr 2023 20:50:00 +0000 Jakub Kicinski wrote:
> On Mon, 3 Apr 2023 11:18:46 +0000 Felix Hüttner wrote:
> > On Sat, 1 Apr 2023 6:25:00 +0000 Jakub Kicinski wrote:
> > > On Fri, 31 Mar 2023 06:25:13 +0000 Felix Hüttner wrote:
> > > > diff --git a/net/core/dev.c b/net/core/dev.c
> > > > index 253584777101..6628323b7bea 100644
> > > > --- a/net/core/dev.c
> > > > +++ b/net/core/dev.c
> > > > @@ -3199,6 +3199,7 @@ static u16 skb_tx_hash(const struct net_device *dev,
> > > >         }
> > > >
> > > >         if (skb_rx_queue_recorded(skb)) {
> > > > +               BUG_ON(unlikely(qcount == 0));
> > >
> > > DEBUG_NET_WARN_ON()
> > >
> >
> > However if this condition triggers we will be permanently stuck in the loop below.
> > From my understading this also means that future calls to `synchronize_net` will never
> finish (as the packet never finishes processing).
> > So the user will quite probably need to restart his system.
> > I find DEBUG_NET_WARN_ON_ONCE to offer too little visiblity as CONFIG_DEBUG_NET is not
> necessarily enabled per default.
> > I as the user would see it as helpful to have this information available without
> additional config flags.
> > I would propose to use WARN_ON_ONCE
>
> skb_tx_hash() may get called a lot, we shouldn't slow it down on
> production systems just to catch buggy drivers, IMO.

Thanks for the clarification.
Will then use DEBUG_NET_WARN_ON_ONCE in v2
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