RE: [PATCH v4] net: stmmac: fix maxmtu assignment to be within valid range

[Kweh, Hock Leong]

> -----Original Message-----
> From: Andy Shevchenko [mailto:andy.shevchenko@xxxxxxxxx]
> Sent: Saturday, January 07, 2017 8:12 AM
> To: Kweh, Hock Leong <hock.leong.kweh@xxxxxxxxx>
> Cc: David S. Miller <davem@xxxxxxxxxxxxx>; Joao Pinto
> <Joao.Pinto@xxxxxxxxxxxx>; Giuseppe CAVALLARO <peppe.cavallaro@xxxxxx>;
> seraphin.bonnaffe@xxxxxx; Jarod Wilson <jarod@xxxxxxxxxx>; Alexandre
> TORGUE <alexandre.torgue@xxxxxxxxx>; Joachim Eastwood
> <manabian@xxxxxxxxx>; Niklas Cassel <niklas.cassel@xxxxxxxx>; Johan Hovold
> <johan@xxxxxxxxxx>; Pavel Machek <pavel@xxxxxx>; lars.persson@xxxxxxxx;
> netdev <netdev@xxxxxxxxxxxxxxx>; LKML <linux-kernel@xxxxxxxxxxxxxxx>
> Subject: Re: [PATCH v4] net: stmmac: fix maxmtu assignment to be within valid
> range
> 
> On Sat, Jan 7, 2017 at 10:10 AM, Kweh, Hock Leong
> <hock.leong.kweh@xxxxxxxxx> wrote:
> > From: "Kweh, Hock Leong" <hock.leong.kweh@xxxxxxxxx>
> >
> > There is no checking valid value of maxmtu when getting it from device tree.
> > This resolution added the checking condition to ensure the assignment is
> > made within a valid range.
> 
> > changelog v4:
> > * add print warning message when maxmtu > max_mtu as well
> 
> Yep.
> 
> > * add maxmtu = JUMBO_LEN into each *_default_data() at stmmac_pci.c
> 
> Yep.
> 
> But see comment below.
> 
> P.S. And perhaps next time send into our internal mailing list first for review.
> 
> > @@ -3345,8 +3345,14 @@ int stmmac_dvr_probe(struct device *device,
> >                 ndev->max_mtu = JUMBO_LEN;
> >         else
> >                 ndev->max_mtu = SKB_MAX_HEAD(NET_SKB_PAD + NET_IP_ALIGN);
> > -       if (priv->plat->maxmtu < ndev->max_mtu)
> > +       if ((priv->plat->maxmtu < ndev->max_mtu) &&
> > +           (priv->plat->maxmtu >= ndev->min_mtu))
> >                 ndev->max_mtu = priv->plat->maxmtu;
> 
> > +       else if ((priv->plat->maxmtu < ndev->min_mtu) ||
> > +                (priv->plat->maxmtu > ndev->max_mtu))
> > +               netdev_warn(priv->dev,
> 
> What is the difference to just 'else'? (Returning back to my initial
> proposal, I don't remember telling anything about 'else if' concept)
> 

When priv->plat->maxmtu == ndev->max_mtu will not be a warning message.

Oh NO ... it is a valid case for priv->plat->maxmtu > ndev->max_mtu if the
assignment of ndev->max_mtu is using SKB_MAX_HEAD(NET_SKB_PAD + NET_IP_ALIGN),
which is < JUMBO_LEN, then priv->plat->maxmtu > ndev->max_mtu is valid.
Revert back and submit V5. Thanks.

> > +                           "%s: warning: maxmtu having invalid value (%d)\n",
> > +                           __func__, priv->plat->maxmtu);
> 
> --
> With Best Regards,
> Andy Shevchenko