[PATCH 06/13] drm: add minor-lookup/release helpers

[David Herrmann]

Hi

On Fri, Feb 21, 2014 at 8:09 AM, Thierry Reding
<thierry.reding at gmail.com> wrote:
> On Wed, Jan 29, 2014 at 03:01:53PM +0100, David Herrmann wrote:
> [...]
>> diff --git a/drivers/gpu/drm/drm_stub.c b/drivers/gpu/drm/drm_stub.c
>> index c51333e..d3232b6 100644
>> --- a/drivers/gpu/drm/drm_stub.c
>> +++ b/drivers/gpu/drm/drm_stub.c
>> @@ -356,6 +356,45 @@ static void drm_unplug_minor(struct drm_minor *minor)
>>  }
>>
>>  /**
>> + * drm_minor_acquire - Acquire a DRM minor
>> + * @minor_id: Minor ID of the DRM-minor
>> + *
>> + * Looks up the given minor-ID and returns the respective DRM-minor object. The
>> + * refence-count of the underlying device is increased so you must release this
>> + * object with drm_minor_release().
>> + *
>> + * As long as you hold this minor, it is guaranteed that the object and the
>> + * minor->dev pointer will stay valid! However, the device may get unplugged and
>> + * unregistered while you hold the minor.
>> + *
>> + * Returns:
>> + * Pointer to minor-object with increased device-refcount, or PTR_ERR on
>> + * failure.
>> + */
>> +struct drm_minor *drm_minor_acquire(unsigned int minor_id)
>> +{
>> +     struct drm_minor *minor;
>> +
>> +     minor = idr_find(&drm_minors_idr, minor_id);
>> +     if (!minor)
>> +             return ERR_PTR(-ENODEV);
>> +
>> +     drm_dev_ref(minor->dev);
>
> Is it possible that somebody would drop the last reference on the device
> right between the idr_find() call and drm_dev_ref()? In which case both
> the device and the minor will have become invalid when drm_dev_ref() is
> called.

No, it's locked via the drm_global_mutex. And later I introduce a
spinlock here that protects this in case we remove the global lock.

Thanks
David