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

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Message-ID: <20180228133131.0df907ff.cohuck@redhat.com>
Date:   Wed, 28 Feb 2018 13:31:31 +0100
From:   Cornelia Huck <cohuck@...hat.com>
To:     Arvind Yadav <arvind.yadav.cs@...il.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 Wed, 28 Feb 2018 17:39:53 +0530
Arvind Yadav <arvind.yadav.cs@...il.com> wrote:

> 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.

You don't need to do a put_device() after your device_unregister(),
that's all managed by the driver core.