netdev - Re: [PATCH] net/mlx4_en: Fix an error handling path in 'mlx4_en_init

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Date:   Thu, 10 May 2018 16:35:43 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Yuval Shaia <yuval.shaia@...cle.com>
Cc:     davem@...emloft.net, tariqt@...lanox.com, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] net/mlx4_en: Fix an error handling path in
 'mlx4_en_init_netdev()'

Le 10/05/2018 à 15:38, Yuval Shaia a écrit :
> On Thu, May 10, 2018 at 09:02:26AM +0200, Christophe JAILLET wrote:
>> If an error occurs, 'mlx4_en_destroy_netdev()' is called.
>> It then calls 'mlx4_en_free_resources()' which does the needed resources
>> cleanup.
>>
>> So, doing some explicit kfree in the error handling path would lead to
>> some double kfree.
> Patch make sense but what's bothering me is that mlx4_en_free_resources
> loops on the entire array, assuming !priv->tx_ring[t] means entry is
> allocated but the existing code does not assume that, see [1]. So i looked
> to see where tx_ring array is zeroed and didn't find it.
>
> Am i missing something here.
My understanding is that the array is zeoed at line 3289, when the whole 
priv struct is memset(0)'ed (also done in alloc_etherdev_mqs but leaving 
an explicit memset help to remind that the struct is zeroed)
If speed matters here (and I don't think so), the memset could be saved 
(the mlx4_en_priv struct is quite big after all), but at least a comment 
should remind that it is initialized within alloc_etherdev_mqs.

CJ


>> Simplify code to avoid such a case.
>>
>> Fixes: 67f8b1dcb9ee ("net/mlx4_en: Refactor the XDP forwarding rings scheme")
>> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
>> ---
>>   drivers/net/ethernet/mellanox/mlx4/en_netdev.c | 8 +-------
>>   1 file changed, 1 insertion(+), 7 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
>> index e0adac4a9a19..9670b33fc9b1 100644
>> --- a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
>> +++ b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
>> @@ -3324,12 +3324,11 @@ int mlx4_en_init_netdev(struct mlx4_en_dev *mdev, int port,
>>   					   MAX_TX_RINGS, GFP_KERNEL);
>>   		if (!priv->tx_ring[t]) {
>>   			err = -ENOMEM;
>> -			goto err_free_tx;
>> +			goto out;
>>   		}
>>   		priv->tx_cq[t] = kzalloc(sizeof(struct mlx4_en_cq *) *
>>   					 MAX_TX_RINGS, GFP_KERNEL);
>>   		if (!priv->tx_cq[t]) {
>> -			kfree(priv->tx_ring[t]);
>>   			err = -ENOMEM;
>>   			goto out;
>>   		}
>> @@ -3582,11 +3581,6 @@ int mlx4_en_init_netdev(struct mlx4_en_dev *mdev, int port,
>>   
>>   	return 0;
>>   
>> -err_free_tx:
>> -	while (t--) {
> [1]
>
>> -		kfree(priv->tx_ring[t]);
>> -		kfree(priv->tx_cq[t]);
>> -	}
>>   out:
>>   	mlx4_en_destroy_netdev(dev);
>>   	return err;
>> -- 
>> 2.17.0
>>
>> --
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