Re: [PATCH] staging: most: video: replace BUG_ON with WARN_ON_ONCE and add recovery

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Apr 20, 2026 at 11:35:03AM +0000, Matan Cohen wrote:
> BUG_ON() halts the kernel unconditionally. The check after
> most_deregister_component() guards against a bug in mostcore: it
> currently does not call disconnect_channel() for linked channels on
> deregistration, so if that ever changes unexpectedly, video_devices
> could be non-empty.
> 
> Replace BUG_ON with WARN_ON_ONCE so the kernel stays up, and add a
> recovery path that drains and frees any remaining devices to avoid
> memory leaks in that error case.
> 
> Also document what the spinlock and mutex in struct most_video_dev
> each protect.
> ---
>  drivers/staging/most/video/video.c | 19 ++++++++++++++++---
>  1 file changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/staging/most/video/video.c b/drivers/staging/most/video/video.c
> index 04351f8ccccf1..4ade49569bd63 100644
> --- a/drivers/staging/most/video/video.c
> +++ b/drivers/staging/most/video/video.c
> @@ -33,14 +33,14 @@ struct most_video_dev {
>  	bool mute;
>  
>  	struct list_head pending_mbos;
> -	spinlock_t list_lock;
> +	spinlock_t list_lock; /* protects pending_mbos and mute */
>  
>  	struct v4l2_device v4l2_dev;
>  	atomic_t access_ref;
>  	struct video_device *vdev;
>  	unsigned int ctrl_input;
>  
> -	struct mutex lock;
> +	struct mutex lock; /* v4l2 device lock */
>  
>  	wait_queue_head_t wait_data;
>  };
> @@ -577,7 +577,20 @@ static void __exit comp_exit(void)
>  
>  	most_deregister_configfs_subsys(&comp);
>  	most_deregister_component(&comp);
> -	BUG_ON(!list_empty(&video_devices));
> +
> +	if (WARN_ON_ONCE(!list_empty(&video_devices))) {
> +		/* clean up any devices unexpectedly added during deregister phase */
> +		spin_lock_irq(&list_lock);
> +		list_replace_init(&video_devices, &free_list);
> +		spin_unlock_irq(&list_lock);
> +
> +		list_for_each_entry_safe(mdev, tmp, &free_list, list) {
> +			list_del_init(&mdev->list);
> +			comp_unregister_videodev(mdev);
> +			v4l2_device_disconnect(&mdev->v4l2_dev);
> +			v4l2_device_put(&mdev->v4l2_dev);
> +		}
> +	}
>  }
>  
>  module_init(comp_init);
> -- 
> 2.43.0
> 
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
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If you wish to discuss this problem further, or you have questions about
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thanks,

greg k-h's patch email bot