linux-kernel - Re: [PATCH v6 3/4] media: uvcvideo: Avoid race condition during unregister

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Message-ID: <20240925192056.GC30399@pendragon.ideasonboard.com>
Date: Wed, 25 Sep 2024 22:20:56 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Ricardo Ribalda <ribalda@...omium.org>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>,
	Guenter Roeck <linux@...ck-us.net>,
	Tomasz Figa <tfiga@...omium.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Hans Verkuil <hverkuil-cisco@...all.nl>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	Sean Paul <seanpaul@...omium.org>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH v6 3/4] media: uvcvideo: Avoid race condition during
 unregister

Hi Ricardo,

Thank you for the patch.

I'd write "during status unregister" in the subject line.

On Fri, Jun 14, 2024 at 12:41:29PM +0000, Ricardo Ribalda wrote:
> The control events are handled asynchronously by the driver. Once the
> control event are handled, the urb is re-submitted.
> 
> If we simply kill the urb, there is a chance that a control event is
> waiting to be processed, which will re-submit the urb after the device is
> disconnected.
> 
> uvc_status_suspend() flushes the async controls and stops the urb in a
> correct manner.

"Fix this by calling uvc_status_suspend(), which flushes the async
controls and kills the URB in a race-free manner."

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

> Reviewed-by: Sergey Senozhatsky <senozhatsky@...omium.org>
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
>  drivers/media/usb/uvc/uvc_status.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_status.c b/drivers/media/usb/uvc/uvc_status.c
> index 375a95dd3011..8fd8250110e2 100644
> --- a/drivers/media/usb/uvc/uvc_status.c
> +++ b/drivers/media/usb/uvc/uvc_status.c
> @@ -294,7 +294,7 @@ int uvc_status_init(struct uvc_device *dev)
>  
>  void uvc_status_unregister(struct uvc_device *dev)
>  {
> -	usb_kill_urb(dev->int_urb);
> +	uvc_status_suspend(dev);
>  	uvc_input_unregister(dev);
>  }
>  

-- 
Regards,

Laurent Pinchart