linux-kernel - Re: [PATCH] media: vb2: frame_vector.c: replace WARN

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Message-ID: <7ad62d3c-7bcb-5248-4fd9-bcab819d51d3@redhat.com>
Date:   Thu, 17 Aug 2023 13:21:25 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Hans Verkuil <hverkuil-cisco@...all.nl>,
        Linux Media Mailing List <linux-media@...r.kernel.org>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Jan Kara <jack@...e.cz>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] media: vb2: frame_vector.c: replace WARN_ONCE with a
 comment

On 17.08.23 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@...all.nl>
> ---
> 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;
>   }
> 

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb