linux-kernel - Re: [PATCH v4 6/6] media: uvcvideo: Move decode processing to process context

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Date:   Tue, 6 Nov 2018 15:13:55 +0000
From:   Kieran Bingham <kieran.bingham@...asonboard.com>
To:     Tomasz Figa <tfiga@...gle.com>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        g.liakhovetski@....de, olivier.braun@...reolabs.com,
        troy.kisky@...ndarydevices.com,
        Randy Dunlap <rdunlap@...radead.org>, philipp.zabel@...il.com,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 6/6] media: uvcvideo: Move decode processing to process
 context

Hi Tomasz,

On 07/08/2018 10:54, Tomasz Figa wrote:
> Hi Kieran,
> 
> On Wed, Mar 28, 2018 at 1:47 AM Kieran Bingham
> <kieran.bingham@...asonboard.com> wrote:
> [snip]
>> @@ -1544,25 +1594,29 @@ static int uvc_alloc_urb_buffers(struct uvc_streaming *stream,
>>   */
>>  static void uvc_uninit_video(struct uvc_streaming *stream, int free_buffers)
>>  {
>> -       struct urb *urb;
>> -       unsigned int i;
>> +       struct uvc_urb *uvc_urb;
>>
>>         uvc_video_stats_stop(stream);
>>
>> -       for (i = 0; i < UVC_URBS; ++i) {
>> -               struct uvc_urb *uvc_urb = &stream->uvc_urb[i];
>> +       /*
>> +        * We must poison the URBs rather than kill them to ensure that even
>> +        * after the completion handler returns, any asynchronous workqueues
>> +        * will be prevented from resubmitting the URBs
>> +        */
>> +       for_each_uvc_urb(uvc_urb, stream)
>> +               usb_poison_urb(uvc_urb->urb);
>>
>> -               urb = uvc_urb->urb;
>> -               if (urb == NULL)
>> -                       continue;
>> +       flush_workqueue(stream->async_wq);
>>
>> -               usb_kill_urb(urb);
>> -               usb_free_urb(urb);
>> +       for_each_uvc_urb(uvc_urb, stream) {
>> +               usb_free_urb(uvc_urb->urb);
>>                 uvc_urb->urb = NULL;
>>         }
>>
>>         if (free_buffers)
>>                 uvc_free_urb_buffers(stream);
>> +
>> +       destroy_workqueue(stream->async_wq);
> 
> In our testing, this function ends up being called twice, if before
> suspend the camera is streaming and if the camera disconnects between
> suspend and resume. This is because uvc_video_suspend() calls this
> function (with free_buffers = 0), but uvc_video_resume() wouldn't call
> uvc_init_video() due to an earlier failure and uvc_v4l2_release()
> would end up calling this function again, while the workqueue is
> already destroyed.
> 
> The following diff seems to take care of it:

Thank you for this. After discussing with Laurent, I have gone with the
approach of keeping the workqueue for the lifetime of the stream, rather
than the lifetime of the streamon.


> 
> 8<~~~
> diff --git a/drivers/media/usb/uvc/uvc_video.c
> b/drivers/media/usb/uvc/uvc_video.c
> index c5e0ab564b1a..6fb890c8ba67 100644
> --- a/drivers/media/usb/uvc/uvc_video.c
> +++ b/drivers/media/usb/uvc/uvc_video.c
> @@ -1493,10 +1493,11 @@ static void uvc_uninit_video(struct
> uvc_streaming *stream, int free_buffers)
>                uvc_urb->urb = NULL;
>        }
> 
> -       if (free_buffers)
> +       if (free_buffers) {
>                uvc_free_urb_buffers(stream);
> -
> -       destroy_workqueue(stream->async_wq);
> +               destroy_workqueue(stream->async_wq);
> +               stream->async_wq = NULL;
> +       }
> }
> 
> /*
> @@ -1648,10 +1649,12 @@ static int uvc_init_video(struct uvc_streaming
> *stream, gfp_t gfp_flags)
> 
>        uvc_video_stats_start(stream);
> 
> -       stream->async_wq = alloc_workqueue("uvcvideo", WQ_UNBOUND | WQ_HIGHPRI,
> -                       0);
> -       if (!stream->async_wq)
> -               return -ENOMEM;
> +       if (!stream->async_wq) {
> +               stream->async_wq = alloc_workqueue("uvcvideo",
> +                                                  WQ_UNBOUND | WQ_HIGHPRI, 0);
> +               if (!stream->async_wq)
> +                       return -ENOMEM;
> +       }
> 
>        if (intf->num_altsetting > 1) {
>                struct usb_host_endpoint *best_ep = NULL;
> ~~~>8
> 
> Best regards,
> Tomasz
> 

-- 
Regards
--
Kieran