On 10/19/2013 12:22 PM, Ricardo Ribalda Delgado wrote:
On Sat, Oct 19, 2013 at 11:55 AM, Sylwester Nawrocki
<sylvester.nawrocki@xxxxxxxxx> wrote:
> On 10/14/2013 09:41 AM, Ricardo Ribalda Delgado wrote:
>>
>> vb2_fop_relase does not held the lock although it is modifying the
>> queue->owner field.
> [...]
>> diff --git a/drivers/media/v4l2-core/videobuf2-core.c
>> b/drivers/media/v4l2-core/videobuf2-core.c
>> index 9fc4bab..3a961ee 100644
>> --- a/drivers/media/v4l2-core/videobuf2-core.c
>> +++ b/drivers/media/v4l2-core/videobuf2-core.c
>> @@ -2588,8 +2588,15 @@ int vb2_fop_release(struct file *file)
>> struct video_device *vdev = video_devdata(file);
>>
>> if (file->private_data == vdev->queue->owner) {
>> + struct mutex *lock;
>> +
>> + lock = vdev->queue->lock ? vdev->queue->lock : vdev->lock;
>> + if (lock)
>> + mutex_lock(lock);
>> vb2_queue_release(vdev->queue);
>> vdev->queue->owner = NULL;
>> + if (lock)
>> + mutex_unlock(lock);
>> }
>> return v4l2_fh_release(file);
>> }
>
>
> It seems you didn't inspect all users of vb2_fop_release(). There are 3
> drivers
> that don't assign vb2_fop_release() to struct v4l2_file_operations directly
> but
> instead call it from within its own release() handler. Two of them do call
> vb2_fop_release() with the video queue lock already held.
>
> $ git grep -n vb2_fop_rel -- drivers/media/
>
> drivers/media/platform/exynos4-is/fimc-capture.c:552: ret =
> vb2_fop_release(file);
> drivers/media/platform/exynos4-is/fimc-lite.c:549: vb2_fop_release(file);
>
Very good catch, thanks!
> A rather ugly solution would be to open code the vb2_fop_release() function
> in those driver, like in below patch (untested). Unless there are better
> proposals I would queue the patch as below together with the $subject patch
> upstream.
IMHO this will lead to the same type of mistakes in the future.
What about creating a function __vb2_fop_release that does exactly
the same as the original function but with an extra parameter bool
lock_held
vb2_fop_release will be a wrapper for that funtion with lock_held== false
Hmm, the parameter would be telling whether the lock is already held ?
Perhaps
we should inverse its meaning and it should indicate whether
vb2_fop_release()
should be taking the lock internally ? It seems to me more straightforward.
drivers that overload the fop_release and need to hold the lock will
call the __ function with lock_held= true
What do you think?
I was also considering this, it's probably better. I'm not sure about
exporting
functions prefixed with __ though. And the locking becomes less clear
with such
functions proliferation.
Anyway, I'm in general personally OK with having an additional version like:
__vb2_fop_release(struct file *filp, bool lock);
Regards,
Sylwester
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