linux-kernel - Re: [PATCH net] net: sunhme: Return an error when we are out of slots

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Date:   Wed, 22 Feb 2023 22:19:09 +0100
From:   Simon Horman <simon.horman@...igine.com>
To:     Sean Anderson <seanga2@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Rolf Eike Beer <eike-kernel@...tec.de>,
        kernel test robot <lkp@...el.com>,
        Dan Carpenter <error27@...il.com>
Subject: Re: [PATCH net] net: sunhme: Return an error when we are out of slots

On Wed, Feb 22, 2023 at 04:07:15PM -0500, Sean Anderson wrote:
> On 2/22/23 15:59, Simon Horman wrote:
> > On Wed, Feb 22, 2023 at 12:09:35PM -0500, Sean Anderson wrote:
> > > We only allocate enough space for four devices when the parent is a QFE. If
> > > we couldn't find a spot (because five devices were created for whatever
> > > reason), we would not return an error from probe(). Return ENODEV, which
> > > was what we did before.
> > > 
> > > Fixes: 96c6e9faecf1 ("sunhme: forward the error code from pci_enable_device()")
> > 
> > I think the hash for that commit is acb3f35f920b.
> 
> Ah, sorry that's my local copy. The upstream commit is as you noted.
> 
> > 
> > However, I also think this problem was introduced by the first hunk of
> > 5b3dc6dda6b1 ("sunhme: Regularize probe errors").
> > 
> > Which is:
> > 
> > --- a/drivers/net/ethernet/sun/sunhme.c
> > +++ b/drivers/net/ethernet/sun/sunhme.c
> > @@ -2945,7 +2945,6 @@ static int happy_meal_pci_probe(struct pci_dev *pdev,
> >   	if (err)
> >   		goto err_out;
> >   	pci_set_master(pdev);
> > -	err = -ENODEV;
> >   	if (!strcmp(prom_name, "SUNW,qfe") || !strcmp(prom_name, "qfe")) {
> >   		qp = quattro_pci_find(pdev);
> > 
> 
> Yes. That's the one I should have blamed.
> 
> > Which leads me to wonder if simpler fixes would be either:
> > 
> > 1) Reverting the hunk above
> > 2) Or, more in keeping with the rest of that patch,
> >     explicitly setting err before branching to err_out,
> >     as you your patch does, but without other logic changes.
> 
> >     Something like this (*compile tested only!*:
> > 
> > diff --git a/drivers/net/ethernet/sun/sunhme.c b/drivers/net/ethernet/sun/sunhme.c
> > index 1c16548415cd..2409e7d6c29e 100644
> > --- a/drivers/net/ethernet/sun/sunhme.c
> > +++ b/drivers/net/ethernet/sun/sunhme.c
> > @@ -2863,8 +2863,10 @@ static int happy_meal_pci_probe(struct pci_dev *pdev,
> >   			if (!qp->happy_meals[qfe_slot])
> >   				break;
> > -		if (qfe_slot == 4)
> > +		if (qfe_slot == 4) {
> > +			err = -ENOMEM;
> >   			goto err_out;
> > +		}
> >   	}
> >   	dev = devm_alloc_etherdev(&pdev->dev, sizeof(struct happy_meal));
> 
> That's of course simpler, but this also does some cleanup to make it more
> obvious what's going on.

Sure. I do think there is merit in a minimal change as a fix.
But I don't feel strongly about it.

> > Also, I am curious why happy_meal_pci_probe() doesn't just return instaed
> > of branching to err_out. As err_out only returns err.  I guess there is a
> > reason for it. But simply returning would probably simplify error handling.
> > (I'm not suggesting that approach for this fix.)
> 
> I think it's because there used to be cleanup in err_out. But you're right,
> we can just return directly and avoid a goto.

Makes sense, thanks.

> --Sean
> 
> > > Reported-by: kernel test robot <lkp@...el.com>
> > > Reported-by: Dan Carpenter <error27@...il.com>
> > > Signed-off-by: Sean Anderson <seanga2@...il.com>
> > > ---
> > > 
> > >   drivers/net/ethernet/sun/sunhme.c | 7 ++++---
> > >   1 file changed, 4 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/net/ethernet/sun/sunhme.c b/drivers/net/ethernet/sun/sunhme.c
> > > index 1c16548415cd..523e26653ec8 100644
> > > --- a/drivers/net/ethernet/sun/sunhme.c
> > > +++ b/drivers/net/ethernet/sun/sunhme.c
> > > @@ -2861,12 +2861,13 @@ static int happy_meal_pci_probe(struct pci_dev *pdev,
> > >   		for (qfe_slot = 0; qfe_slot < 4; qfe_slot++)
> > >   			if (!qp->happy_meals[qfe_slot])
> > > -				break;
> > > +				goto found_slot;
> > > -		if (qfe_slot == 4)
> > > -			goto err_out;
> > > +		err = -ENODEV;
> > > +		goto err_out;
> > >   	}
> > > +found_slot:
> > >   	dev = devm_alloc_etherdev(&pdev->dev, sizeof(struct happy_meal));
> > >   	if (!dev) {
> > >   		err = -ENOMEM;
> > > -- 
> > > 2.37.1
> > > 
>