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

[Tony Krowiak]

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