linux-kernel - Re: [PATCH] media: cx18: Don't check for address of video

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Date:   Mon, 1 Oct 2018 10:30:54 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Nathan Chancellor <natechancellor@...il.com>,
        Andy Walls <awalls@...metrocast.net>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH] media: cx18: Don't check for address of video_dev

On 09/21/2018 09:57 PM, Nathan Chancellor wrote:
> Clang warns that the address of a pointer will always evaluated as true
> in a boolean context.
> 
> drivers/media/pci/cx18/cx18-driver.c:1255:23: warning: address of
> 'cx->streams[i].video_dev' will always evaluate to 'true'
> [-Wpointer-bool-conversion]
>                 if (&cx->streams[i].video_dev)
>                 ~~   ~~~~~~~~~~~~~~~^~~~~~~~~
> 1 warning generated.
> 
> Presumably, the contents of video_dev should have been checked, not the
> address. This check has been present since 2009, introduced by commit
> 21a278b85d3c ("V4L/DVB (11619): cx18: Simplify the work handler for
> outgoing mailbox commands")
> 
> Reported-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
> 
> Alternatively, this if statement could just be removed since it has
> evaluated to true since 2009 and I assume some issue with this would
> have been discovered by now.
> 
>  drivers/media/pci/cx18/cx18-driver.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/media/pci/cx18/cx18-driver.c b/drivers/media/pci/cx18/cx18-driver.c
> index 56763c4ea1a7..753a37c7100a 100644
> --- a/drivers/media/pci/cx18/cx18-driver.c
> +++ b/drivers/media/pci/cx18/cx18-driver.c
> @@ -1252,7 +1252,7 @@ static void cx18_cancel_out_work_orders(struct cx18 *cx)
>  {
>  	int i;
>  	for (i = 0; i < CX18_MAX_STREAMS; i++)
> -		if (&cx->streams[i].video_dev)
> +		if (cx->streams[i].video_dev)

This should read:

		if (cx->streams[i].video_dev.v4l2_dev)

If cx->streams[i].video_dev.v4l2_dev == NULL, then the stream is not in use
and there is no need to cancel any work.

Can you post a v2?

>  			cancel_work_sync(&cx->streams[i].out_work_order);
>  }
>  
> 

Regards,

	Hans