linux-kernel - Re: [PATCH 03/35] media: uvcvideo: Refactor iterators

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Message-ID: <20240418110438.GX12561@pendragon.ideasonboard.com>
Date: Thu, 18 Apr 2024 14:04:38 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Ricardo Ribalda <ribalda@...omium.org>
Cc: Martin Tuma <martin.tuma@...iteqautomotive.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Hans Verkuil <hverkuil-cisco@...all.nl>,
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Subject: Re: [PATCH 03/35] media: uvcvideo: Refactor iterators

Hi Ricardo,

Thank you for the patch.

On Mon, Apr 15, 2024 at 07:34:20PM +0000, Ricardo Ribalda wrote:
> Avoid using the iterators after the list_for_each() constructs.
> This patch should be a NOP, but makes cocci, happier:
> 
> drivers/media/usb/uvc/uvc_ctrl.c:1861:44-50: ERROR: invalid reference to the index variable of the iterator on line 1850
> drivers/media/usb/uvc/uvc_ctrl.c:2195:17-23: ERROR: invalid reference to the index variable of the iterator on line 2179
> 
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
>  drivers/media/usb/uvc/uvc_ctrl.c | 24 +++++++++++++-----------
>  1 file changed, 13 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> index e59a463c2761..a4a987913430 100644
> --- a/drivers/media/usb/uvc/uvc_ctrl.c
> +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> @@ -1850,16 +1850,18 @@ int __uvc_ctrl_commit(struct uvc_fh *handle, int rollback,
>  	list_for_each_entry(entity, &chain->entities, chain) {

If we really want to ensure the iterator won't be used after the loop,
it could be declared in the loop statement itself, now that the kernel
has switched to a newer C version.

>  		ret = uvc_ctrl_commit_entity(chain->dev, entity, rollback,
>  					     &err_ctrl);
> -		if (ret < 0)
> +		if (ret < 0) {
> +			if (ctrls)
> +				ctrls->error_idx =
> +					uvc_ctrl_find_ctrl_idx(entity, ctrls,
> +							       err_ctrl);
>  			goto done;
> +		}
>  	}
>  
>  	if (!rollback)
>  		uvc_ctrl_send_events(handle, ctrls->controls, ctrls->count);
>  done:
> -	if (ret < 0 && ctrls)
> -		ctrls->error_idx = uvc_ctrl_find_ctrl_idx(entity, ctrls,
> -							  err_ctrl);
>  	mutex_unlock(&chain->ctrl_mutex);
>  	return ret;
>  }
> @@ -2165,7 +2167,7 @@ static int uvc_ctrl_init_xu_ctrl(struct uvc_device *dev,
>  int uvc_xu_ctrl_query(struct uvc_video_chain *chain,
>  	struct uvc_xu_control_query *xqry)
>  {
> -	struct uvc_entity *entity;
> +	struct uvc_entity *entity, *iter;
>  	struct uvc_control *ctrl;
>  	unsigned int i;
>  	bool found;
> @@ -2175,16 +2177,16 @@ int uvc_xu_ctrl_query(struct uvc_video_chain *chain,
>  	int ret;
>  
>  	/* Find the extension unit. */
> -	found = false;
> -	list_for_each_entry(entity, &chain->entities, chain) {
> -		if (UVC_ENTITY_TYPE(entity) == UVC_VC_EXTENSION_UNIT &&
> -		    entity->id == xqry->unit) {
> -			found = true;
> +	entity = NULL;
> +	list_for_each_entry(iter, &chain->entities, chain) {

Same here, iter could be declared in the loop.

> +		if (UVC_ENTITY_TYPE(iter) == UVC_VC_EXTENSION_UNIT &&
> +		    iter->id == xqry->unit) {
> +			entity = iter;
>  			break;
>  		}
>  	}
>  
> -	if (!found) {
> +	if (!entity) {
>  		uvc_dbg(chain->dev, CONTROL, "Extension unit %u not found\n",
>  			xqry->unit);
>  		return -ENOENT;
> 

-- 
Regards,

Laurent Pinchart