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SubjectRe: [PATCH] [media] media-entity: only call dev_dbg_obj if mdev is not NULL
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Hi Sakari,

On 2017-04-07 04:40 AM, Sakari Ailus wrote:
> Hi Helen,
>
> On Thu, Apr 06, 2017 at 04:32:00PM -0300, Helen Koike wrote:
>> Fix kernel Oops NULL pointer deference
>> Call dev_dbg_obj only after checking if gobj->mdev is not NULL
>>
>> Signed-off-by: Helen Koike <helen.koike@collabora.com>
>> ---
>> drivers/media/media-entity.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/media/media-entity.c b/drivers/media/media-entity.c
>> index 5640ca2..bc44193 100644
>> --- a/drivers/media/media-entity.c
>> +++ b/drivers/media/media-entity.c
>> @@ -199,12 +199,12 @@ void media_gobj_create(struct media_device *mdev,
>>
>> void media_gobj_destroy(struct media_gobj *gobj)
>> {
>> - dev_dbg_obj(__func__, gobj);
>> -
>> /* Do nothing if the object is not linked. */
>> if (gobj->mdev == NULL)
>> return;
>>
>> + dev_dbg_obj(__func__, gobj);
>> +
>> gobj->mdev->topology_version++;
>>
>> /* Remove the object from mdev list */
>
> Where is media_gobj_destroy() called with an object with NULL mdev?
>
> I do not object to the change, but would like to know because I don't think
> it's supposed to happen.


This happens when media_device_unregister(mdev) is called before
unregistering the subdevices v4l2_device_unregister_subdev(sd) (which
should be possible).

v4l2_device_unregister_subdev(sd) ends up calling v4l2_device_release()
that calls media_device_unregister_entity() again (previously called by
media_device_unregister(mdev)

Helen

>
> There are issues though, until the patches fixing object referencing are
> finished and merged. Unfortunately I haven't been able to work on those
> recently, will pick them up again soon...
>

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