linux-kernel - Re: [PATCH] media: videobuf2: Fix IS_ERR checking in vb2_vmalloc_put

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Date:   Mon, 2 Oct 2023 12:16:36 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Ma Ke <make_ruc2021@....com>, tfiga@...omium.org,
        m.szyprowski@...sung.com, mchehab@...nel.org
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: videobuf2: Fix IS_ERR checking in
 vb2_vmalloc_put_userptr()

Hi Ma Ke,

On 24/09/2023 14:44, Ma Ke wrote:
> In order to avoid error pointers from frame_vector_pages(), we could
> use IS_ERR() to check the return value to fix this. This checking
> operation could make sure that vector contains pages.
> 
> Signed-off-by: Ma Ke <make_ruc2021@....com>
> ---
>  drivers/media/common/videobuf2/videobuf2-vmalloc.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/media/common/videobuf2/videobuf2-vmalloc.c b/drivers/media/common/videobuf2/videobuf2-vmalloc.c
> index 7c635e292106..c37775080aff 100644
> --- a/drivers/media/common/videobuf2/videobuf2-vmalloc.c
> +++ b/drivers/media/common/videobuf2/videobuf2-vmalloc.c
> @@ -134,6 +134,7 @@ static void vb2_vmalloc_put_userptr(void *buf_priv)
>  	if (!buf->vec->is_pfns) {
>  		n_pages = frame_vector_count(buf->vec);
>  		pages = frame_vector_pages(buf->vec);
> +		BUG_ON(IS_ERR(pages));
>  		if (vaddr)
>  			vm_unmap_ram((void *)vaddr, n_pages);
>  		if (buf->dma_dir == DMA_FROM_DEVICE ||

The use of BUG_ON is discouraged in the kernel. I did notice that is it
also used in the put_userptr callback in videobuf2-dma-contig.c.

I think it is much better to do something like this:

        if (!buf->vec->is_pfns) {
                n_pages = frame_vector_count(buf->vec);
                if (vaddr)
                        vm_unmap_ram((void *)vaddr, n_pages);
                if (buf->dma_dir == DMA_FROM_DEVICE ||
                    buf->dma_dir == DMA_BIDIRECTIONAL) {
	                pages = frame_vector_pages(buf->vec);
			if (!WARN_ON_ONCE(IS_ERR(pages)))
	                        for (i = 0; i < n_pages; i++)
        	                        set_page_dirty_lock(pages[i]);
		}
	} else {

and do something similar in videobuf2-dma-contig.c.

Regards,

	Hans