Re: [PATCH] dma-buf: Make DMABUF_DEBUG default to y on DEBUG_KERNEL kernels

["Diederik de Haas" <diederik@cknow-tech.com>]

On Mon Sep 7, 2026 at 4:00 AM CEST, Karl Mehltretter wrote:
> Commit 646013f513f3 ("dma-buf: enable DMABUF_DEBUG by default on DEBUG
> kernels") changed the default of DMABUF_DEBUG to "y if DEBUG", but no
> Kconfig symbol DEBUG exists, so the option has had no default since.
>
> Use DEBUG_KERNEL, the Kconfig symbol for a debug kernel.

I wondered why since 7.3-rc4 when playing videos I got a WHOLE lot of the
following error messages, which weren't there with 7.3-rc3:

  [drm:rockchip_gem_iommu_map [rockchipdrm]] *ERROR* failed to map buffer: size=0 request_size=3956736
  [drm:rockchip_gem_prime_import_sg_table [rockchipdrm]] *ERROR* failed to import sg table: -12

Both come from ``drivers/gpu/drm/rockchip/rockchip_drm_gem.c``.

The value of request_size varies sometimes; I see ``request_size=8294400``
the most. When playing a video (with mpv with v4l2request functionality, but
I think that doesn't matter), I see a whole bunch of these errors and then
it stays 'silent', but I get another stream of them when I resize the window
(ie I'm toggling between windowed and full-screen).
It doesn't take long before dmesg only consists of these errors.

The 'playing video' is likely important; when I just start sway I don't see
those errors. It's only when I start a video that those pop up.

My kernel (config) is based on Debian's and that has ``DEBUG_KERNEL=y`` at
least since 2008 and due to this patch/commit, ``DMABUF_DEBUG`` got turned on.
When I explicitly disable ``DMABUF_DEBUG``, I no longer see those errors.

Whether that fixes or just hides a problem, I'll leave that for others to
decide.

> Fixes: 646013f513f3 ("dma-buf: enable DMABUF_DEBUG by default on DEBUG kernels")
> Assisted-by: LLM
> Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
> ---
> This enables the dma-buf debug checks on every CONFIG_DEBUG_KERNEL
> configuration, which is what 646013f513f3 set out to do. If that is too
> broad today, the alternative is to restore the previous
> "default y if DMA_API_DEBUG".

My 0.02:
That change landed in 7.0-rc1 albeit it didn't have the effect it intended
to achieve. An -rc1 version seems like the right version to land such a change.

I'm not in favor of this just popping up in 7.3-rc4 while -rc3 did NOT have
that affect. With an -rc1 you'd expect major changes, but in this case I
accidentally stumbled upon it while trying out something else.

Cheers,
  Diederik

>  drivers/dma-buf/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
> index 7efc0f0d0712..e4f078a326a4 100644
> --- a/drivers/dma-buf/Kconfig
> +++ b/drivers/dma-buf/Kconfig
> @@ -43,7 +43,7 @@ config UDMABUF
>  config DMABUF_DEBUG
>  	bool "DMA-BUF debug checks"
>  	depends on DMA_SHARED_BUFFER
> -	default y if DEBUG
> +	default y if DEBUG_KERNEL
>  	help
>  	  This option enables additional checks for DMA-BUF importers and
>  	  exporters. Specifically it validates that importers do not peek at the
>
> base-commit: 986c24e0fe44f844b44d365b71ce831947f50298