Re: [URGENT] [PATCH] vb2: Don't WARN when v4l2_buffer.bytesused is 0 for multiplanar buffers

[Hans Verkuil <hverkuil@xs4all.nl>]

On 06/19/2015 01:50 PM, Laurent Pinchart wrote:
> Commit f61bf13b6a07 ("[media] vb2: add allow_zero_bytesused flag to the
> vb2_queue struct") added a WARN_ONCE to catch usage of a deprecated API
> using a zero value for v4l2_buffer.bytesused.
> 
> However, the condition is checked incorrectly, as the v4L2_buffer
> bytesused field is supposed to be ignored for multiplanar buffers. This
> results in spurious warnings when using the multiplanar API.
> 
> Fix it by checking v4l2_buffer.bytesused for uniplanar buffers and
> v4l2_plane.bytesused for multiplanar buffers.
> 
> Fixes: f61bf13b6a07 ("[media] vb2: add allow_zero_bytesused flag to the vb2_queue struct")
> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> ---
>  drivers/media/v4l2-core/videobuf2-core.c | 33 ++++++++++++++++++++++----------
>  1 file changed, 23 insertions(+), 10 deletions(-)
> 
> The bug was introduced in v4.1-rc1. It would be quite bad if it made it to
> v4.1 as many users will start complaining.
> 
> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
> index d835814a24d4..93b315459098 100644
> --- a/drivers/media/v4l2-core/videobuf2-core.c
> +++ b/drivers/media/v4l2-core/videobuf2-core.c
> @@ -1242,6 +1242,23 @@ void vb2_discard_done(struct vb2_queue *q)
>  }
>  EXPORT_SYMBOL_GPL(vb2_discard_done);
>  
> +static void vb2_warn_zero_bytesused(struct vb2_buffer *vb)
> +{
> +	static bool __check_once __read_mostly;

Why the underscores? Why the __read_mostly?

Just say: 'static bool check_once;'

Much more readable, and there really is no benefit whatsoever for adding
a __read_mostly attribute here.

> +
> +	if (__check_once)
> +		return;
> +
> +	__check_once = true;
> +	__WARN();
> +
> +	pr_warn_once("use of bytesused == 0 is deprecated and will be removed in the future,\n");

This can be pr_warn now. pr_warn_once will implicitly only do another 'check_once' check
with its own 'check_once' variable.

> +	if (vb->vb2_queue->allow_zero_bytesused)
> +		pr_warn_once("use VIDIOC_DECODER_CMD(V4L2_DEC_CMD_STOP) instead.\n");
> +	else
> +		pr_warn_once("use the actual size instead.\n");
> +}

Regards,

	Hans

> +
>  /**
>   * __fill_vb2_buffer() - fill a vb2_buffer with information provided in a
>   * v4l2_buffer by the userspace. The caller has already verified that struct
> @@ -1252,16 +1269,6 @@ static void __fill_vb2_buffer(struct vb2_buffer *vb, const struct v4l2_buffer *b
>  {
>  	unsigned int plane;
>  
> -	if (V4L2_TYPE_IS_OUTPUT(b->type)) {
> -		if (WARN_ON_ONCE(b->bytesused == 0)) {
> -			pr_warn_once("use of bytesused == 0 is deprecated and will be removed in the future,\n");
> -			if (vb->vb2_queue->allow_zero_bytesused)
> -				pr_warn_once("use VIDIOC_DECODER_CMD(V4L2_DEC_CMD_STOP) instead.\n");
> -			else
> -				pr_warn_once("use the actual size instead.\n");
> -		}
> -	}
> -
>  	if (V4L2_TYPE_IS_MULTIPLANAR(b->type)) {
>  		if (b->memory == V4L2_MEMORY_USERPTR) {
>  			for (plane = 0; plane < vb->num_planes; ++plane) {
> @@ -1302,6 +1309,9 @@ static void __fill_vb2_buffer(struct vb2_buffer *vb, const struct v4l2_buffer *b
>  				struct v4l2_plane *pdst = &v4l2_planes[plane];
>  				struct v4l2_plane *psrc = &b->m.planes[plane];
>  
> +				if (psrc->bytesused == 0)
> +					vb2_warn_zero_bytesused(vb);
> +
>  				if (vb->vb2_queue->allow_zero_bytesused)
>  					pdst->bytesused = psrc->bytesused;
>  				else
> @@ -1336,6 +1346,9 @@ static void __fill_vb2_buffer(struct vb2_buffer *vb, const struct v4l2_buffer *b
>  		}
>  
>  		if (V4L2_TYPE_IS_OUTPUT(b->type)) {
> +			if (b->bytesused == 0)
> +				vb2_warn_zero_bytesused(vb);
> +
>  			if (vb->vb2_queue->allow_zero_bytesused)
>  				v4l2_planes[0].bytesused = b->bytesused;
>  			else
> 

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