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 16:07:15 -0500
From:   Sean Anderson <seanga2@...il.com>
To:     Simon Horman <simon.horman@...igine.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 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.

> 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.

--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
>>