netdev - Re: [PATCH net-next v4 4/4] net: ocelot: add FDMA support

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Date:   Sat, 4 Dec 2021 11:51:52 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Clément Léger <clement.leger@...tlin.com>
CC:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        "UNGLinuxDriver@...rochip.com" <UNGLinuxDriver@...rochip.com>,
        Andrew Lunn <andrew@...n.ch>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Denis Kirjanov <dkirjanov@...e.de>,
        Julian Wiedmann <jwi@...ux.ibm.com>
Subject: Re: [PATCH net-next v4 4/4] net: ocelot: add FDMA support

On Sat, Dec 04, 2021 at 07:52:06AM +0100, Clément Léger wrote:
> > +void ocelot_fdma_netdev_init(struct ocelot *ocelot, struct net_device *dev)
> > +{
> > +	struct ocelot_fdma *fdma = ocelot->fdma;
> > +
> > +	dev->needed_headroom = OCELOT_TAG_LEN;
> > +	dev->needed_tailroom = ETH_FCS_LEN;
> > +
> > +	if (fdma->napi_init)
> > +		return;
> > +
> > +	fdma->napi_init = true;
> > +	netif_napi_add(dev, &ocelot->napi, ocelot_fdma_napi_poll,
> > +		       OCELOT_FDMA_WEIGHT);
> > +}
> > +
> > +void ocelot_fdma_netdev_deinit(struct ocelot *ocelot, struct net_device *dev)
> > +{
> > +	struct ocelot_fdma *fdma = ocelot->fdma;
> > +
> > +	if (fdma->napi_init) {
> > +		netif_napi_del(&ocelot->napi);
> > +		fdma->napi_init = false;
> > +	}
> 
> Using a boolean  is acutally a bad idea, if the last netdev
> registration fails in ocelot, then the napi context will be deleted.
> The net_device should actually be used.

I think that you could try to call netif_napi_del() only if dev == napi->dev.
Because, as you say, if the NAPI structure has been added to the first
net device, and the registration of subsequent net devices fails, that
NAPI might actually even be in use by now, we should not disturb it.