Re: [PATCH] media: uvcvideo: Stop stream during unregister

[Hans Verkuil]

Hi Laurent,

On 10/10/2024 20:23, Laurent Pinchart wrote:
> Hi Hans,
> 
> On Mon, Oct 07, 2024 at 04:53:30PM +0200, Hans Verkuil wrote:
>> On 07/10/2024 16:44, Laurent Pinchart wrote:
>>> On Mon, Oct 07, 2024 at 09:46:47AM +0200, Hans Verkuil wrote:
>>>> Hi Laurent,
>>>>
>>>> Just a reminder: I have extensively reviewed this patch here:
>>>>
>>>> https://lore.kernel.org/linux-media/f4c49ccf-9dc9-475a-8fc9-4ef4c85a729a@xxxxxxxxx/
>>>>
>>>> and here (specifically checking for mmap() races):
>>>>
>>>> https://lore.kernel.org/linux-media/1a10530f-b4bb-4244-84ff-1f2365ae9b23@xxxxxxxxx/
>>>>
>>>> To the best of my ability I believe this patch is correct.
>>>>
>>>> Unless you have any additional concerns I plan to take this patch as a fix for
>>>> v6.12 on Monday next week.
>>>
>>> I thought we had an agreement that I could submit an alternative fix for
>>> v6.12. Can you therefore delay merging this patch until v6.12-rc6 ?
>>
>> Correct, if there is indeed something wrong with this patch and an alternative
>> fix is needed (or at least should be considered).
>>
>> But I see nothing wrong with this patch after careful analysis. If you disagree
>> with my analysis, and you think I missed a possible race condition, then that's
>> a reason to wait for a better fix. Otherwise there is no point in waiting any longer.
> 
> I'm in Montréal this week for the GStreamer conference and XDC. I'll
> reply to your last e-mail early next week, let's make a decision then.
> Surely this can wait until -rc4 before being merged ?

Sure, no problem.

Enjoy Montréal!

	Hans

> 
>>>> Alternatively, you can make a PR for 6.12 with this patch that I can pull from.
>>>>
>>>> Regards,
>>>>
>>>> 	Hans
>>>>
>>>> On 26/09/2024 07:59, Ricardo Ribalda wrote:
>>>>> uvc_unregister_video() can be called asynchronously from
>>>>> uvc_disconnect(). If the device is still streaming when that happens, a
>>>>> plethora of race conditions can occur.
>>>>>
>>>>> Make sure that the device has stopped streaming before exiting this
>>>>> function.
>>>>>
>>>>> If the user still holds handles to the driver's file descriptors, any
>>>>> ioctl will return -ENODEV from the v4l2 core.
>>>>>
>>>>> This change makes uvc more consistent with the rest of the v4l2 drivers
>>>>> using the vb2_fop_* and vb2_ioctl_* helpers.
>>>>>
>>>>> Reviewed-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
>>>>> Suggested-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
>>>>> Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
>>>>> ---
>>>>> This patch was part of the series:
>>>>> https://patchwork.linuxtv.org/project/linux-media/list/?series=13064
>>>>>
>>>>> Moved out from it to ease the review.
>>>>> ---
>>>>>  drivers/media/usb/uvc/uvc_driver.c | 32 +++++++++++++++++++++++++++++++-
>>>>>  1 file changed, 31 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
>>>>> index f0febdc08c2d..bee150b852e4 100644
>>>>> --- a/drivers/media/usb/uvc/uvc_driver.c
>>>>> +++ b/drivers/media/usb/uvc/uvc_driver.c
>>>>> @@ -1919,11 +1919,41 @@ static void uvc_unregister_video(struct uvc_device *dev)
>>>>>  	struct uvc_streaming *stream;
>>>>>  
>>>>>  	list_for_each_entry(stream, &dev->streams, list) {
>>>>> +		/* Nothing to do here, continue. */
>>>>>  		if (!video_is_registered(&stream->vdev))
>>>>>  			continue;
>>>>>  
>>>>> +		/*
>>>>> +		 * For stream->vdev we follow the same logic as:
>>>>> +		 * vb2_video_unregister_device().
>>>>> +		 */
>>>>> +
>>>>> +		/* 1. Take a reference to vdev */
>>>>> +		get_device(&stream->vdev.dev);
>>>>> +
>>>>> +		/* 2. Ensure that no new ioctls can be called. */
>>>>>  		video_unregister_device(&stream->vdev);
>>>>> -		video_unregister_device(&stream->meta.vdev);
>>>>> +
>>>>> +		/* 3. Wait for old ioctls to finish. */
>>>>> +		mutex_lock(&stream->mutex);
>>>>> +
>>>>> +		/* 4. Stop streaming. */
>>>>> +		uvc_queue_release(&stream->queue);
>>>>> +
>>>>> +		mutex_unlock(&stream->mutex);
>>>>> +
>>>>> +		put_device(&stream->vdev.dev);
>>>>> +
>>>>> +		/*
>>>>> +		 * For stream->meta.vdev we can directly call:
>>>>> +		 * vb2_video_unregister_device().
>>>>> +		 */
>>>>> +		vb2_video_unregister_device(&stream->meta.vdev);
>>>>> +
>>>>> +		/*
>>>>> +		 * Now both vdevs are not streaming and all the ioctls will
>>>>> +		 * return -ENODEV.
>>>>> +		 */
>>>>>  
>>>>>  		uvc_debugfs_cleanup_stream(stream);
>>>>>  	}
>>>>>
>>>>> ---
>>>>> base-commit: 81ee62e8d09ee3c7107d11c8bbfd64073ab601ad
>>>>> change-id: 20240926-uvc_stop_streaming-6e9fd20e97bc
>