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

Cornelia Huck
2018-06-13T12:12:21Z

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.

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