linux-kernel - Re: [PATCH net 1/3] net/mlx5e: Harden uplink netdev access against device unbind

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Message-ID: <9bbac284-48b8-4377-85f9-9dd3c60410cf@nvidia.com>
Date: Thu, 11 Sep 2025 15:09:53 +0800
From: Jianbo Liu <jianbol@...dia.com>
To: Jakub Kicinski <kuba@...nel.org>
CC: Tariq Toukan <tariqt@...dia.com>, Eric Dumazet <edumazet@...gle.com>,
	Paolo Abeni <pabeni@...hat.com>, Andrew Lunn <andrew+netdev@...n.ch>, "David
 S. Miller" <davem@...emloft.net>, Saeed Mahameed <saeedm@...dia.com>, "Leon
 Romanovsky" <leon@...nel.org>, Mark Bloch <mbloch@...dia.com>,
	<netdev@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Gal Pressman <gal@...dia.com>
Subject: Re: [PATCH net 1/3] net/mlx5e: Harden uplink netdev access against
 device unbind



On 9/11/2025 8:45 AM, Jakub Kicinski wrote:
> On Wed, 10 Sep 2025 11:23:09 +0800 Jianbo Liu wrote:
>> On 9/10/2025 9:23 AM, Jakub Kicinski wrote:
>>> On Mon, 8 Sep 2025 13:07:04 +0300 Tariq Toukan wrote:
>>>> +	struct net_device *netdev = mlx5_uplink_netdev_get(dev);
>>>> +	struct mlx5e_priv *priv;
>>>> +	int err;
>>>> +
>>>> +	if (!netdev)
>>>> +		return 0;
>>>
>>> Please don't call in variable init functions which require cleanup
>>> or error checking.
>>
>> But in this function, a NULL return from mlx5_uplink_netdev_get is a
>> valid condition where it should simply return 0. No cleanup or error
>> check is needed.
> 
> You have to check if it succeeded, and if so, you need to clean up
> later. Do no hide meaningful code in variable init.

My focus was on the NULL case, but I see now that the real issue is 
ensuring the corresponding cleanup (_put) happens on the successful 
path. Hiding the _get call in the initializer makes that less clear.

I will refactor the code to follow the correct pattern, like this:

struct net_device *netdev;

netdev = mlx5_uplink_netdev_get(dev);
if (!netdev)
	return 0;

Thank you for the explanation.