linux-kernel - Re: [PATCH 03/20] media: usb: uvc_ctrl.c: add temp variable for list iteration

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Date:   Sat, 8 Aug 2020 23:47:21 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     "Daniel W. S. Almeida" <dwlsalmeida@...il.com>
Cc:     skhan@...uxfoundation.org,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/20] media: usb: uvc_ctrl.c: add temp variable for list
 iteration

Hi Daniel,

On Sat, Aug 08, 2020 at 11:40:13PM +0300, Laurent Pinchart wrote:
> On Fri, Aug 07, 2020 at 05:35:30AM -0300, Daniel W. S. Almeida wrote:
> > From: "Daniel W. S. Almeida" <dwlsalmeida@...il.com>
> > 
> > Fixes the following coccinelle report:
> > 
> > drivers/media/usb/uvc/uvc_ctrl.c:1860:5-11:
> > ERROR: invalid reference to the index variable of the iterator on line 1854
> > 
> > By introducing a temporary variable to iterate the list.
> > 
> > Do not dereference the 'entity' pointer if it is not found in the list.
> > 
> > Found using - Coccinelle (http://coccinelle.lip6.fr)
> > 
> > Signed-off-by: Daniel W. S. Almeida <dwlsalmeida@...il.com>
> > ---
> >  drivers/media/usb/uvc/uvc_ctrl.c | 13 ++++++++-----
> >  1 file changed, 8 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> > index e399b9fad757..567bdedc2ff2 100644
> > --- a/drivers/media/usb/uvc/uvc_ctrl.c
> > +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> > @@ -1842,7 +1842,8 @@ 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 = NULL;
> > +	struct uvc_entity *cursor = NULL;
> 
> cursor doesn't have to be initialized to NULL.
> 
> It may be a style preference, but instead of a cursor variable that
> doesn't tell in its name what it refers to, I'd prefer a
> 
> 	bool found = false;
> 
> >  	struct uvc_control *ctrl;
> >  	unsigned int i, found = 0;
> >  	u32 reqflags;
> > @@ -1851,13 +1852,15 @@ int uvc_xu_ctrl_query(struct uvc_video_chain *chain,
> >  	int ret;
> >  
> >  	/* Find the extension unit. */
> > -	list_for_each_entry(entity, &chain->entities, chain) {
> > -		if (UVC_ENTITY_TYPE(entity) == UVC_VC_EXTENSION_UNIT &&
> > -		    entity->id == xqry->unit)
> > +	list_for_each_entry(cursor, &chain->entities, chain) {
> > +		if (UVC_ENTITY_TYPE(cursor) == UVC_VC_EXTENSION_UNIT &&
> > +		    cursor->id == xqry->unit) {
> 
> All this would keep using entity.
> 
> > +			entity = cursor;
> 
> And this would be replaced with
> 
> 			found = true;
> 
> >  			break;
> > +		    }

I forgot to mention that the indentation is incorrect here.

> >  	}
> >  
> > -	if (entity->id != xqry->unit) {
> > +	if (!entity || entity->id != xqry->unit) {
> 
> The second part of the check isn't needed, it was only meant to check if
> the entity has been found.
> 
> Here, we'd have 
> 
> 	if (!found) {
> 
> I'f you're OK with these changes there's no need to resubmit, I can
> update when applying. Please let me know how you'd like to proceed.
> 
> >  		uvc_trace(UVC_TRACE_CONTROL, "Extension unit %u not found.\n",
> >  			xqry->unit);
> >  		return -ENOENT;

-- 
Regards,

Laurent Pinchart