Re: [PATCH 1/1] media: v4l2-subdev: Fail {enable,disable}_streams and s_streaming nicely

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Mon, May 04, 2026 at 03:35:03PM +0300, Sakari Ailus wrote:
> If a sub-device does not set enable_streams() and disable_streams() pad
> ops while it sets the s_stream() video op to
> v4l2_subdev_s_stream_helper(), enabling or disabling streaming either way
> on the sub-device will result calling v4l2_subdev_s_stream_helper() and
> v4l2_subdev_{enable,disable}_streams() recursively, exhausting the stack.
> Return -ENOIOCTLCMD in this case to handle the situation gracefully.
> 
> Reported-by: David Heidelberg <david@ixit.cz>
> Fixes: b62949ddaa52 ("media: subdev: Support single-stream case in v4l2_subdev_enable/disable_streams()")
> Cc: stable@vger.kernel.org
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> ---
> since v2:
> 
> - Move the check, with checking the pad ops, to
>   v4l2_subdev_s_stream_helper().
> 
>  drivers/media/v4l2-core/v4l2-subdev.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
> index 831c69c958b8..3b726f044d3f 100644
> --- a/drivers/media/v4l2-core/v4l2-subdev.c
> +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> @@ -2504,6 +2504,10 @@ int v4l2_subdev_s_stream_helper(struct v4l2_subdev *sd, int enable)
>  	u64 source_mask = 0;
>  	int pad_index = -1;
>  
> +	if (WARN_ON_ONCE(!v4l2_subdev_has_op(sd, pad, enable_streams) ||
> +			 !v4l2_subdev_has_op(sd, pad, disable_streams)))

Is this indicates a clear bug, I would use WARN_ON() instead of
WARN_ON_ONCE(). Up to you.

Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>

> +		return -ENOIOCTLCMD;
> +
>  	/*
>  	 * Find the source pad. This helper is meant for subdevs that have a
>  	 * single source pad, so failures shouldn't happen, but catch them

-- 
Regards,

Laurent Pinchart