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

Pierre Morel
2018-06-13T12:02:11Z

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 ?

>
>>>
>>>>
>>>>> +
>>>>> +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