linux-kernel - Re: [PATCH v2 4/4] media: uvcvideo: Remove redundant NULL assignment

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Message-ID: <20241128212628.GD25731@pendragon.ideasonboard.com>
Date: Thu, 28 Nov 2024 23:26:28 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Ricardo Ribalda <ribalda@...omium.org>
Cc: Hans de Goede <hdegoede@...hat.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Guennadi Liakhovetski <guennadi.liakhovetski@...el.com>,
	Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/4] media: uvcvideo: Remove redundant NULL assignment

Hi Ricardo,

Thank you for the patch.

On Wed, Nov 27, 2024 at 12:14:52PM +0000, Ricardo Ribalda wrote:
> ctrl->handle will only be different than NULL for controls that have
> mappings. This is because that assignment is only done inside
> uvc_ctrl_set() for mapped controls.

That seems right. I checked the unplug paths, and the mappings are
destroyed from uvc_delete(), after all file handles get closed.

I think this patch should go first in the series, as otherwise there's a
temporary state where you rely on handle never being touched without
holding the proper lock, and this code path violates that requirement.
Is there anything I may be missing that would cause issues with
bisection if I move this patch at the beginning of the series ?

> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>

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

> ---
>  drivers/media/usb/uvc/uvc_ctrl.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> index 99ddc5e9dff8..b9c9ff629ab6 100644
> --- a/drivers/media/usb/uvc/uvc_ctrl.c
> +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> @@ -1645,10 +1645,8 @@ bool uvc_ctrl_status_event_async(struct urb *urb, struct uvc_video_chain *chain,
>  	struct uvc_device *dev = chain->dev;
>  	struct uvc_ctrl_work *w = &dev->async_ctrl;
>  
> -	if (list_empty(&ctrl->info.mappings)) {
> -		ctrl->handle = NULL;
> +	if (list_empty(&ctrl->info.mappings))
>  		return false;
> -	}
>  
>  	w->data = data;
>  	w->urb = urb;

-- 
Regards,

Laurent Pinchart