Re: [PATCH] media: vb2: frame_vector.c: replace WARN_ONCE with a comment

[Hans Verkuil]

On 17/08/2023 12:41, Hans Verkuil wrote:
> The WARN_ONCE was issued also in cases that had nothing to do with VM_IO
> (e.g. if the start address was just a random value and uaccess fails with
> -EFAULT).
> 
> There are no reports of WARN_ONCE being issued for actual VM_IO cases, so
> just drop it and instead add a note to the comment before the function.
> 
> Signed-off-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>

I forgot to add:

Reported-by: Yikebaer Aizezi <yikebaer61@xxxxxxxxx>


> ---
> diff --git a/drivers/media/common/videobuf2/frame_vector.c b/drivers/media/common/videobuf2/frame_vector.c
> index 0f430ddc1f67..fd87747be9b1 100644
> --- a/drivers/media/common/videobuf2/frame_vector.c
> +++ b/drivers/media/common/videobuf2/frame_vector.c
> @@ -31,6 +31,10 @@
>   * different type underlying the specified range of virtual addresses.
>   * When the function isn't able to map a single page, it returns error.
>   *
> + * Note that get_vaddr_frames() cannot follow VM_IO mappings. It used
> + * to be able to do that, but that could (racily) return non-refcounted
> + * pfns.
> + *
>   * This function takes care of grabbing mmap_lock as necessary.
>   */
>  int get_vaddr_frames(unsigned long start, unsigned int nr_frames, bool write,
> @@ -59,8 +63,6 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames, bool write,
>  	if (likely(ret > 0))
>  		return ret;
> 
> -	/* This used to (racily) return non-refcounted pfns. Let people know */
> -	WARN_ONCE(1, "get_vaddr_frames() cannot follow VM_IO mapping");
>  	vec->nr_frames = 0;
>  	return ret ? ret : -EFAULT;
>  }
>