Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 22 Jan 2021 12:47:51 +0100
From:   Marc Kleine-Budde <mkl@pengutronix.de>
To:     Jakub Kicinski <kuba@kernel.org>
Cc:     Oleksij Rempel <o.rempel@pengutronix.de>,
        "David S. Miller" <davem@davemloft.net>,
        Oliver Hartkopp <socketcan@hartkopp.net>,
        Robin van der Gracht <robin@protonic.nl>,
        syzbot+5138c4dd15a0401bec7b@syzkaller.appspotmail.com,
        kernel@pengutronix.de, linux-can@vger.kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH net 1/2] net: introduce CAN specific pointer in the
 struct net_device
Message-ID: <20210122114751.scp23qtyqmsol5h5@hardanger.blackshift.org>
References: <20210115143036.31275-1-o.rempel@pengutronix.de>
 <20210115160723.7abd75ec@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha512;
        protocol="application/pgp-signature"; boundary="7lq5rzmnwt7rxwny"
Content-Disposition: inline
In-Reply-To: <20210115160723.7abd75ec@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Precedence: bulk


--7lq5rzmnwt7rxwny
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Fri, Jan 15, 2021 at 04:07:23PM -0800, Jakub Kicinski wrote:
> On Fri, 15 Jan 2021 15:30:35 +0100 Oleksij Rempel wrote:
> > Since 20dd3850bcf8 ("can: Speed up CAN frame receiption by using
> > ml_priv") the CAN framework uses per device specific data in the AF_CAN
> > protocol. For this purpose the struct net_device->ml_priv is used. Later
> > the ml_priv usage in CAN was extended for other users, one of them being
> > CAN_J1939.
> >=20
> > Later in the kernel ml_priv was converted to an union, used by other
> > drivers. E.g. the tun driver started storing it's stats pointer.
> >=20
> > Since tun devices can claim to be a CAN device, CAN specific protocols
> > will wrongly interpret this pointer, which will cause system crashes.
> > Mostly this issue is visible in the CAN_J1939 stack.
> >=20
> > To fix this issue, we request a dedicated CAN pointer within the
> > net_device struct.
>=20
> No strong objection, others already added their pointers, but=20
> I wonder if we can't save those couple of bytes by adding a
> ml_priv_type, to check instead of dev->type? And leave it 0
> for drivers using stats?

Sounds good.

If we want to save even more bytes, it might be possible, to move the
wireless and wpan pointers to ml_priv.

	struct wireless_dev	*ieee80211_ptr;
	struct wpan_dev		*ieee802154_ptr;

> That way other device types which are limited by all being=20
> ARPHDR_ETHER can start using ml_priv as well?
>=20
> > +#if IS_ENABLED(CONFIG_CAN)
> > +	struct can_ml_priv	*can;
> > +#endif
>=20
> Perhaps put it next to all the _ptr fields?

Makes sense. Oleksij will resping the series.

regards,
Marc

--=20
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |

--7lq5rzmnwt7rxwny
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----

iQEzBAABCgAdFiEEK3kIWJt9yTYMP3ehqclaivrt76kFAmAKu2QACgkQqclaivrt
76nqjgf/WQLZN1prQ6aSfMcYqQnSDRDOM9Ey3xx+A5Fu6VBsf5pbGFkDSykCVVqe
dNXGNgen6JqaJ2woIvKMzR4WOSy/8OIb1A8H3yhY6OCdaCaB0jyqFOx+25wrmGY9
VebJ7qel8Vs/xfijb/N25BQv7HWe6uJZtqpfQBX54rvNyRLpry1jCGkxkp5U8ylC
BrzEyd/ouKIbl5aEJDY5eWyZ7ZRVJ+scBc8JkHK7Ls4m1lj3z4isRR31X7h5cB2j
4PgCO/OEkvOiePj9K1NeziKwE6IY8HBlm3Ryop/EJeVcwg5T/plcM8RLi8+r0rKc
UqAdUnwgSZnPF4wWagZXe+PtPj80bA==
=6QPW
-----END PGP SIGNATURE-----

--7lq5rzmnwt7rxwny--