linux-kernel - Re: [PATCH v5 04/13] s390: vfio-ap: base implementation of VFIO AP device driver

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Date:   Wed, 13 Jun 2018 14:16:55 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>
Cc:     Tony Krowiak <akrowiak@...ux.vnet.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, freude@...ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, borntraeger@...ibm.com,
        kwankhede@...dia.com, bjsdjshi@...ux.vnet.ibm.com,
        pbonzini@...hat.com, alex.williamson@...hat.com,
        pmorel@...ux.vnet.ibm.com, alifm@...ux.vnet.ibm.com,
        mjrosato@...ux.vnet.ibm.com, jjherne@...ux.vnet.ibm.com,
        thuth@...hat.com, pasic@...ux.vnet.ibm.com, berrange@...hat.com,
        fiuczy@...ux.vnet.ibm.com, buendgen@...ibm.com
Subject: Re: [PATCH v5 04/13] s390: vfio-ap: base implementation of VFIO AP
 device driver

On 13/06/2018 14:12, Cornelia Huck wrote:
> On Wed, 13 Jun 2018 14:01:54 +0200
> Pierre Morel <pmorel@...ux.ibm.com> wrote:
>
>> On 13/06/2018 13:14, Cornelia Huck wrote:
>>> On Wed, 13 Jun 2018 12:54:40 +0200
>>> Pierre Morel <pmorel@...ux.ibm.com> wrote:
>>>   
>>>> On 13/06/2018 09:48, Cornelia Huck wrote:
>>>>> On Wed, 13 Jun 2018 09:41:16 +0200
>>>>> Pierre Morel <pmorel@...ux.ibm.com> wrote:
>>>>>      
>>>>>> On 07/05/2018 17:11, Tony Krowiak wrote:
>>>>>>> Introduces a new AP device driver. This device driver
>>>>>>> is built on the VFIO mediated device framework. The framework
>>>>>>> provides sysfs interfaces that facilitate passthrough
>>>>>>> access by guests to devices installed on the linux host.
>>>>>> ...snip...
>>>>>>      
>>>>>>> +static int vfio_ap_matrix_dev_create(void)
>>>>>>> +{
>>>>>>> +	int ret;
>>>>>>> +
>>>>>>> +	vfio_ap_root_device = root_device_register(VFIO_AP_ROOT_NAME);
>>>>>>> +
>>>>>>> +	if (IS_ERR(vfio_ap_root_device)) {
>>>>>>> +		ret = PTR_ERR(vfio_ap_root_device);
>>>>>>> +		goto done;
>>>>>>> +	}
>>>>>>> +
>>>>>>> +	ap_matrix = kzalloc(sizeof(*ap_matrix), GFP_KERNEL);
>>>>>>> +	if (!ap_matrix) {
>>>>>>> +		ret = -ENOMEM;
>>>>>>> +		goto matrix_alloc_err;
>>>>>>> +	}
>>>>>>> +
>>>>>>> +	ap_matrix->device.type = &vfio_ap_dev_type;
>>>>>>> +	dev_set_name(&ap_matrix->device, "%s", VFIO_AP_DEV_NAME);
>>>>>>> +	ap_matrix->device.parent = vfio_ap_root_device;
>>>>>>> +	ap_matrix->device.release = vfio_ap_matrix_dev_release;
>>>>>>> +	ap_matrix->device.driver = &vfio_ap_drv.driver;
>>>>>>> +
>>>>>>> +	ret = device_register(&ap_matrix->device);
>>>>>>> +	if (ret)
>>>>>>> +		goto matrix_reg_err;
>>>>>>> +
>>>>>>> +	goto done;
>>>>>>> +
>>>>>>> +matrix_reg_err:
>>>>>>> +	put_device(&ap_matrix->device);
>>>>>> Did not see this before but here you certainly want to
>>>>>> do a kfree and not a put_device.
>>>>> No, this must not be a kfree. Once you've tried to register something
>>>>> embedding a struct device with the driver core, you need to use
>>>>> put_device, as another path may have acquired a reference, even if
>>>>> registering ultimately failed. See the comment for device_register().
>>>>> IOW, the code is correct.
>>>> learned something again :) ,
>>>> but still, a kfree is needed for the kzalloc.
>>>> Does'nt it?
>>> No, the put callback for the embedding structure needs to take care of
>>> freeing things. Otherwise it is buggy.
>> Seems buggy to me.
>> How does the put_device knows if it is embedded and then in what it is
>> embedded ?
> It does not need to know; the code registering the structure needs to
> set up device->release correctly.

yes right, thanks.

>
>>>   
>>>>>      
>>>>>>      
>>>>>>> +
>>>>>>> +matrix_alloc_err:
>>>>>>> +	root_device_unregister(vfio_ap_root_device);
>>>>>>> +
>>>>>>> +done:
>>>>>>> +	return ret;
>>>>>>> +}
>>>>>>> +
>>>>>>> +static void vfio_ap_matrix_dev_destroy(struct ap_matrix *ap_matrix)
>>>>>>> +{
>>>>>>> +	device_unregister(&ap_matrix->device);
>>>>>>> +	root_device_unregister(vfio_ap_root_device);
>>>>>> Also here you need a kfree(ap_matrix) too .
>>>>> Same here.
>>>>>      
>>

-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany