netdev - Re: [PATCH] virtio-net: fix the kzalloc/kfree mismatch problem

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Date:   Wed, 2 Jun 2021 15:19:46 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        "Guodeqing (A)" <geffrey.guo@...wei.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Max Gurtovoy <mgurtovoy@...dia.com>,
        "mst@...hat.com" <mst@...hat.com>
Subject: Re: [PATCH] virtio-net: fix the kzalloc/kfree mismatch problem


在 2021/6/2 下午1:50, Leon Romanovsky 写道:
> On Mon, May 24, 2021 at 10:37:14AM +0800, Jason Wang wrote:
>> 在 2021/5/24 上午10:06, Xuan Zhuo 写道:
>>> On Mon, 24 May 2021 01:48:53 +0000, Guodeqing (A) <geffrey.guo@...wei.com> wrote:
>>>>> -----Original Message-----
>>>>> From: Max Gurtovoy [mailto:mgurtovoy@...dia.com]
>>>>> Sent: Sunday, May 23, 2021 15:25
>>>>> To: Guodeqing (A) <geffrey.guo@...wei.com>; mst@...hat.com
>>>>> Cc: jasowang@...hat.com; davem@...emloft.net; kuba@...nel.org;
>>>>> virtualization@...ts.linux-foundation.org; netdev@...r.kernel.org
>>>>> Subject: Re: [PATCH] virtio-net: fix the kzalloc/kfree mismatch problem
>>>>>
>>>>>
>>>>> On 5/22/2021 11:02 AM, guodeqing wrote:
>>>>>> If the virtio_net device does not suppurt the ctrl queue feature, the
>>>>>> vi->ctrl was not allocated, so there is no need to free it.
>>>>> you don't need this check.
>>>>>
>>>>> from kfree doc:
>>>>>
>>>>> "If @objp is NULL, no operation is performed."
>>>>>
>>>>> This is not a bug. I've set vi->ctrl to be NULL in case !vi->has_cvq.
>>>>>
>>>>>
>>>>     yes,  this is not a bug, the patch is just a optimization, because the vi->ctrl maybe
>>>>     be freed which  was not allocated, this may give people a misunderstanding.
>>>>     Thanks.
>>> I think it may be enough to add a comment, and the code does not need to be
>>> modified.
>>>
>>> Thanks.
>>
>> Or even just leave the current code as is. A lot of kernel codes was wrote
>> under the assumption that kfree() should deal with NULL.
> It is not assumption but standard practice that can be seen as side
> effect of "7) Centralized exiting of functions" section of coding-style.rst.
>
> Thanks


I don't see the connection to the centralized exiting.

Something like:

if (foo)
     kfree(foo);

won't break the centralization.

Thanks


>