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SubjectRe: [PATCH v2 2/2] uacce: add uacce driver
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Hi, Greg

On 2019/8/29 下午5:54, Greg Kroah-Hartman wrote:
> On Thu, Aug 29, 2019 at 05:05:13PM +0800, zhangfei wrote:
>> Hi, Greg
>>
>> On 2019/8/28 下午11:22, Greg Kroah-Hartman wrote:
>>> On Wed, Aug 28, 2019 at 09:27:56PM +0800, Zhangfei Gao wrote:
>>>> +struct uacce {
>>>> + const char *drv_name;
>>>> + const char *algs;
>>>> + const char *api_ver;
>>>> + unsigned int flags;
>>>> + unsigned long qf_pg_start[UACCE_QFRT_MAX];
>>>> + struct uacce_ops *ops;
>>>> + struct device *pdev;
>>>> + bool is_vf;
>>>> + u32 dev_id;
>>>> + struct cdev cdev;
>>>> + struct device dev;
>>>> + void *priv;
>>>> + atomic_t state;
>>>> + int prot;
>>>> + struct mutex q_lock;
>>>> + struct list_head qs;
>>>> +};
>>> At a quick glance, this problem really stood out to me. You CAN NOT
>>> have two different objects within a structure that have different
>>> lifetime rules and reference counts. You do that here with both a
>>> 'struct cdev' and a 'struct device'. Pick one or the other, but never
>>> both.
>>>
>>> I would recommend using a 'struct device' and then a 'struct cdev *'.
>>> That way you get the advantage of using the driver model properly, and
>>> then just adding your char device node pointer to "the side" which
>>> interacts with this device.
>>>
>>> Then you might want to call this "struct uacce_device" :)
>> Here the 'struct cdev' and 'struct device' have the same lifetime and
>> refcount.
> No they do not, that's impossible as refcounts are incremented from
> different places (i.e. userspace).
Yes, cdev's refcount is increased by open, from user space.

Not sure whether I understand correctly, Is this correct?

@@ -819,9 +819,10 @@ static int uacce_create_chrdev(struct uacce *uacce)
        if (ret < 0)
                return ret;

-       cdev_init(&uacce->cdev, &uacce_fops);
+       uacce->cdev = cdev_alloc();
+       uacce->cdev->ops = &uacce_fops;
        uacce->dev_id = ret;
-       uacce->cdev.owner = THIS_MODULE;
+       uacce->cdev->owner = THIS_MODULE;
        device_initialize(&uacce->dev);
        uacce->dev.devt = MKDEV(MAJOR(uacce_devt), uacce->dev_id);
        uacce->dev.class = uacce_class;
@@ -829,7 +830,7 @@ static int uacce_create_chrdev(struct uacce *uacce)
        uacce->dev.parent = uacce->pdev;
        uacce->dev.release = uacce_release;
        dev_set_name(&uacce->dev, "%s-%d", uacce->drv_name, uacce->dev_id);
-       ret = cdev_device_add(&uacce->cdev, &uacce->dev);
+       ret = cdev_device_add(uacce->cdev, &uacce->dev);
        if (ret)
                goto err_with_idr;

@@ -843,7 +844,7 @@ static int uacce_create_chrdev(struct uacce *uacce)

 static void uacce_destroy_chrdev(struct uacce *uacce)
 {
-       cdev_device_del(&uacce->cdev, &uacce->dev);
+       cdev_device_del(uacce->cdev, &uacce->dev);
        put_device(&uacce->dev);
 }

diff --git a/include/linux/uacce.h b/include/linux/uacce.h
index 1892b94..39a2c4b 100644
--- a/include/linux/uacce.h
+++ b/include/linux/uacce.h
@@ -155,7 +155,7 @@ struct uacce {
        struct device *pdev;
        bool is_vf;
        u32 dev_id;
-       struct cdev cdev;
+       struct cdev *cdev;

And use struct uacce_device instead of struct uacce

-struct uacce *uacce_register(struct device *parent,
-                            struct uacce_interface *interface);
+struct uacce_device *uacce_register(struct device *parent,
+                                   struct uacce_interface *interface);
>
>> They are allocated with uacce when uacce_register and freed when
>> uacce_unregister.
> And that will not work.
>
>> To make it clear, how about adding this.
>>
>> +static void uacce_release(struct device *dev)
>> +{
>> +       struct uacce *uacce = UACCE_FROM_CDEV_ATTR(dev);
>> +
>> +       idr_remove(&uacce_idr, uacce->dev_id);
>> +       kfree(uacce);
>> +}
>> +
>>  static int uacce_create_chrdev(struct uacce *uacce)
>>  {
>>         int ret;
>> @@ -819,6 +827,7 @@ static int uacce_create_chrdev(struct uacce *uacce)
>>         uacce->dev.class = uacce_class;
>>         uacce->dev.groups = uacce_dev_attr_groups;
>>         uacce->dev.parent = uacce->pdev;
>> +       uacce->dev.release = uacce_release;
> You have to have a release function today, otherwise you will get nasty
> kernel messages from the log. I don't know why you aren't seeing that
> already.
Yes, kernel report warning after using put_device.
>
>>         dev_set_name(&uacce->dev, "%s-%d", uacce->drv_name, uacce->dev_id);
>>         ret = cdev_device_add(&uacce->cdev, &uacce->dev);
>>         if (ret)
>> @@ -835,7 +844,7 @@ static int uacce_create_chrdev(struct uacce *uacce)
>>  static void uacce_destroy_chrdev(struct uacce *uacce)
>>  {
>>         cdev_device_del(&uacce->cdev, &uacce->dev);
>> -       idr_remove(&uacce_idr, uacce->dev_id);
>> +       put_device(&uacce->dev);
>>  }
>>
>>  static int uacce_dev_match(struct device *dev, void *data)
>> @@ -1042,8 +1051,6 @@ void uacce_unregister(struct uacce *uacce)
>>         uacce_destroy_chrdev(uacce);
>>
>>         mutex_unlock(&uacce_mutex);
>> -
>> -       kfree(uacce);
>>  }
>>
>>
>> uacce_destroy_chrdev->put_device(&uacce->dev)->uacce_release->kfree(uacce).
>>
>> And find there are many examples in driver/
>> $ grep -rn cdev_device_add drivers/
>> drivers/rtc/class.c:362:        err = cdev_device_add(&rtc->char_dev,
>> &rtc->dev);
>> rivers/gpio/gpiolib.c:1181:    status = cdev_device_add(&gdev->chrdev,
>> &gdev->dev);
>> drivers/soc/qcom/rmtfs_mem.c:223:       ret =
>> cdev_device_add(&rmtfs_mem->cdev, &rmtfs_mem->dev);
>> drivers/input/joydev.c:989:     error = cdev_device_add(&joydev->cdev,
>> &joydev->dev);
>> drivers/input/mousedev.c:907:   error = cdev_device_add(&mousedev->cdev,
>> &mousedev->dev);
>> drivers/input/evdev.c:1419:     error = cdev_device_add(&evdev->cdev,
>> &evdev->dev);
> Are you sure these all have the full structures inbedded in them?
>
>> like drivers/input/evdev.c,
>> evdev is alloced with initialization of dev and cdev,
>> and evdev is freed in release ops evdev_free
>> struct evdev {
>>         struct device dev;
>>         struct cdev cdev;
>>         ~
> Ick, that too is totally wrong and needs to be fixed.
>
> Please don't copy incorrect code, that's why we review stuff :)
>
OK, understand. Thanks Greg.

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