Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH v5 04/13] s390: vfio-ap: base implementation of VFIO AP
 device driver
To:     pmorel@linux.ibm.com, Cornelia Huck <cohuck@redhat.com>
Cc:     Tony Krowiak <akrowiak@linux.vnet.ibm.com>,
        linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, freude@de.ibm.com, schwidefsky@de.ibm.com,
        heiko.carstens@de.ibm.com, borntraeger@de.ibm.com,
        kwankhede@nvidia.com, bjsdjshi@linux.vnet.ibm.com,
        pbonzini@redhat.com, alex.williamson@redhat.com,
        pmorel@linux.vnet.ibm.com, alifm@linux.vnet.ibm.com,
        mjrosato@linux.vnet.ibm.com, jjherne@linux.vnet.ibm.com,
        thuth@redhat.com, pasic@linux.vnet.ibm.com, berrange@redhat.com,
        fiuczy@linux.vnet.ibm.com, buendgen@de.ibm.com
References: <1525705912-12815-1-git-send-email-akrowiak@linux.vnet.ibm.com>
 <1525705912-12815-5-git-send-email-akrowiak@linux.vnet.ibm.com>
 <889b8d41-e08c-0eb5-2de0-a1d6669a03b3@linux.ibm.com>
 <20180613094812.1fd1846d.cohuck@redhat.com>
 <41e7ccbd-f6f5-ba20-f236-7824c682994d@linux.ibm.com>
 <20180613131402.0305d092.cohuck@redhat.com>
 <7237751c-66b5-d14c-5b71-cc1cfc79db87@linux.ibm.com>
 <20180613141221.5b924348.cohuck@redhat.com>
 <65ec9340-6a25-20ac-3078-f67992d5cc15@linux.ibm.com>
From:   Tony Krowiak <akrowiak@linux.ibm.com>
Date:   Thu, 14 Jun 2018 09:04:12 -0400
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.2.0
MIME-Version: 1.0
In-Reply-To: <65ec9340-6a25-20ac-3078-f67992d5cc15@linux.ibm.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Content-Language: en-US
Message-Id: <6ff0eac2-7c0f-4ab1-6301-c7f6997be591@linux.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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.
>>>
>