linux-kernel - Re: [PATCH] sparc: vio: use put

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Date:   Wed, 25 Apr 2018 09:38:35 -0700
From:   Shannon Nelson <shannon.lee.nelson@...il.com>
To:     arvindY <arvind.yadav.cs@...il.com>
Cc:     Shannon Nelson <shannon.nelson@...cle.com>,
        David Miller <davem@...emloft.net>, jag.raman@...cle.com,
        liam.merwick@...cle.com,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Sparc kernel list <sparclinux@...r.kernel.org>
Subject: Re: [PATCH] sparc: vio: use put_device() instead of kfree()

Oh, yes, there it is, and the pointer to vio_dev_release() was already
set up a little earlier in this function.

Sorry for the noise.
sln

On Wed, Apr 25, 2018 at 8:59 AM, arvindY <arvind.yadav.cs@...il.com> wrote:
>
>
> On Wednesday 25 April 2018 09:14 PM, Shannon Nelson wrote:
>>
>> On 4/25/2018 7:56 AM, Arvind Yadav wrote:
>>>
>>> Never directly free @dev after calling device_register(), even
>>> if it returned an error. Always use put_device() to give up the
>>> reference initialized.
>>>
>>> Signed-off-by: Arvind Yadav <arvind.yadav.cs@...il.com>
>>> ---
>>>   arch/sparc/kernel/vio.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/arch/sparc/kernel/vio.c b/arch/sparc/kernel/vio.c
>>> index 1a0fa10..32bae68 100644
>>> --- a/arch/sparc/kernel/vio.c
>>> +++ b/arch/sparc/kernel/vio.c
>>> @@ -403,7 +403,7 @@ static struct vio_dev *vio_create_one(struct
>>> mdesc_handle *hp, u64 mp,
>>>       if (err) {
>>>           printk(KERN_ERR "VIO: Could not register device %s, err=%d\n",
>>>                  dev_name(&vdev->dev), err);
>>> -        kfree(vdev);
>>> +        put_device(&vdev->dev);
>>
>>
>> Hmmm... I can see why the put_device() might be a good idea, but I think
>> we still need the kfree() so as to not leak the memory that was kzalloc'd
>> above for vdev.
>>
>
> There is no need to call kfree() here. Because put_device()
> will decrement the last reference and then free the memory
> by calling dev->release(It'll call vio_dev_release()).
> Internally put_device() -> kobject_put() -> kobject_cleanup()
> which is responsible to call 'dev -> release' and also free
> other kobject resources.
> If we will call kfree() here, Then It'll be a redundant call.
>
> ~arvind
>
>
>> sln
>>
>>>           return NULL;
>>>       }
>>>       if (vdev->dp)
>>>
>
> --
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-- 
==============================================
Mr. Shannon Nelson         Parents can't afford to be squeamish.