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

Tony Krowiak
2018-06-14T13:04:12Z

On 06/13/2018 08:16 AM, Pierre Morel wrote:
> On 13/06/2018 14:12, Cornelia Huck wrote:
>> On Wed, 13 Jun 2018 14:01:54 +0200
>> Pierre Morel <pmorel@linux.ibm.com> wrote:
>>
>>> On 13/06/2018 13:14, Cornelia Huck wrote:
>>>> On Wed, 13 Jun 2018 12:54:40 +0200
>>>> Pierre Morel <pmorel@linux.ibm.com> wrote:
>>>>> On 13/06/2018 09:48, Cornelia Huck wrote:
>>>>>> On Wed, 13 Jun 2018 09:41:16 +0200
>>>>>> Pierre Morel <pmorel@linux.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.

See the vfio_ap_matrix_dev_release() callback.

>
>
>>
>>>>>>>> +
>>>>>>>> +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.
>>>
>