linux-kernel - Re: [PATCH v5 01/12] media: uvcvideo: Fix race condition handling events

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Message-ID: <X+GokHQbUHcquCnm@pendragon.ideasonboard.com>
Date:   Tue, 22 Dec 2020 10:04:32 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Ricardo Ribalda <ribalda@...omium.org>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 01/12] media: uvcvideo: Fix race condition handling
 events

Hi Ricardo,

Thank you for the patch.

On Mon, Dec 21, 2020 at 05:48:08PM +0100, Ricardo Ribalda wrote:
> The control and its data needs to be copied to the workqueue at the same
> time to avoid half-updates of the events.
> This is, events reported to userspace were the control id does not match
> its value.

Actually, after discussing this with you on IRC, I'm not sure there's a
problem. The URB is resubmitted by uvc_ctrl_status_event_work(), so the
data shouldn't be overwritten before it is processed.

> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
>  drivers/media/usb/uvc/uvc_ctrl.c | 2 +-
>  drivers/media/usb/uvc/uvcvideo.h | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> index 011e69427b7c..aa18dcdf8165 100644
> --- a/drivers/media/usb/uvc/uvc_ctrl.c
> +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> @@ -1332,7 +1332,7 @@ bool uvc_ctrl_status_event(struct urb *urb, struct uvc_video_chain *chain,
>  		return false;
>  	}
>  
> -	w->data = data;
> +	memcpy(w->data, data, ctrl->info.size);
>  	w->urb = urb;
>  	w->chain = chain;
>  	w->ctrl = ctrl;
> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> index a3dfacf069c4..0db6c2e0bd98 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -678,7 +678,7 @@ struct uvc_device {
>  		struct urb *urb;
>  		struct uvc_video_chain *chain;
>  		struct uvc_control *ctrl;
> -		const void *data;
> +		u8 data[UVC_MAX_STATUS_SIZE];
>  	} async_ctrl;
>  };
>  

-- 
Regards,

Laurent Pinchart