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

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Date:   Wed, 25 Apr 2018 21:29:57 +0530
From:   arvindY <arvind.yadav.cs@...il.com>
To:     Shannon Nelson <shannon.nelson@...cle.com>, davem@...emloft.net,
        jag.raman@...cle.com, liam.merwick@...cle.com
Cc:     linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org
Subject: Re: [PATCH] sparc: vio: use put_device() instead of kfree()



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)
>>