netdev - Re: [PATCH] net: iucv: Free memory obtained by kzalloc

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Message-ID: <78058d34-7cbb-a3e6-6471-e001b93a0523@gmail.com>
Date:   Wed, 28 Feb 2018 17:39:53 +0530
From:   Arvind Yadav <arvind.yadav.cs@...il.com>
To:     Cornelia Huck <cohuck@...hat.com>
Cc:     jwi@...ux.vnet.ibm.com, ubraun@...ux.vnet.ibm.com,
        davem@...emloft.net, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] net: iucv: Free memory obtained by kzalloc



On Wednesday 28 February 2018 05:26 PM, Cornelia Huck wrote:
> On Wed, 28 Feb 2018 17:14:55 +0530
> Arvind Yadav <arvind.yadav.cs@...il.com> wrote:
>
>> On Wednesday 28 February 2018 04:00 PM, Cornelia Huck wrote:
>>> On Wed, 28 Feb 2018 15:24:16 +0530
>>> Arvind Yadav <arvind.yadav.cs@...il.com> wrote:
>>>   
>>>> Free memory, if afiucv_iucv_init is not successful and
>>>> removing a IUCV driver.
>>>>
>>>> Signed-off-by: Arvind Yadav <arvind.yadav.cs@...il.com>
>>>> ---
>>>>    net/iucv/af_iucv.c | 5 ++++-
>>>>    1 file changed, 4 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/net/iucv/af_iucv.c b/net/iucv/af_iucv.c
>>>> index 1e8cc7b..eb0995a 100644
>>>> --- a/net/iucv/af_iucv.c
>>>> +++ b/net/iucv/af_iucv.c
>>>> @@ -2433,9 +2433,11 @@ static int afiucv_iucv_init(void)
>>>>    	af_iucv_dev->driver = &af_iucv_driver;
>>>>    	err = device_register(af_iucv_dev);
>>>>    	if (err)
>>>> -		goto out_driver;
>>>> +		goto out_iucv_dev;
>>>>    	return 0;
>>>>    
>>>> +out_iucv_dev:
>>>> +	kfree(af_iucv_dev);
>>>>    out_driver:
>>>>    	driver_unregister(&af_iucv_driver);
>>>>    out_iucv:
>>>> @@ -2496,6 +2498,7 @@ static void __exit afiucv_exit(void)
>>>>    {
>>>>    	if (pr_iucv) {
>>>>    		device_unregister(af_iucv_dev);
>>>> +		kfree(af_iucv_dev);
>>>>    		driver_unregister(&af_iucv_driver);
>>>>    		pr_iucv->iucv_unregister(&af_iucv_handler, 0);
>>>>    		symbol_put(iucv_if);
>>> No, you must not use kfree() after you called device_register() (even
>>> if it was not successful!) -- see the comment for device_register().
>> Yes, Your are right. First we need to call put_device() then kfree().
>> I will send updated patch.
> No, that's not correct, either. device_register() will give up any
> reference it obtained, and the caller did not obtain any additional
> reference, so a put_device() would be wrong. A kfree() on a refcounted
> structure is wrong as well.
If you will see the comment for device_register() (drivers/base/core.c)
there is mentioned that
'NOTE: _Never_ directly free @dev after calling this function, even
if it returned an error! Always use put_device() to give up the
reference initialized in this function instead.'
But as per you comment. we should not use.
Thanks,