linux-kernel - Re: [PATCH v4 08/13] drm/v3d: Fix builds with CONFIG_TRANSPARENT

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Message-ID: <20251015201737.3956f801@fedora>
Date: Wed, 15 Oct 2025 20:17:37 +0200
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Loïc Molinari <loic.molinari@...labora.com>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
 <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David Airlie
 <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Jani Nikula
 <jani.nikula@...ux.intel.com>, Joonas Lahtinen
 <joonas.lahtinen@...ux.intel.com>, Rodrigo Vivi <rodrigo.vivi@...el.com>,
 Tvrtko Ursulin <tursulin@...ulin.net>, Rob Herring <robh@...nel.org>,
 Steven Price <steven.price@....com>, Liviu Dudau <liviu.dudau@....com>,
 Melissa Wen <mwen@...lia.com>, Maíra Canal
 <mcanal@...lia.com>, Hugh Dickins <hughd@...gle.com>, Baolin Wang
 <baolin.wang@...ux.alibaba.com>, Andrew Morton <akpm@...ux-foundation.org>,
 Al Viro <viro@...iv.linux.org.uk>, Mikołaj Wasiak
 <mikolaj.wasiak@...el.com>, Christian Brauner <brauner@...nel.org>, Nitin
 Gote <nitin.r.gote@...el.com>, Andi Shyti <andi.shyti@...ux.intel.com>,
 Jonathan Corbet <corbet@....net>, Christopher Healy <healych@...zon.com>,
 Matthew Wilcox <willy@...radead.org>, Bagas Sanjaya <bagasdotme@...il.com>,
 linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 intel-gfx@...ts.freedesktop.org, linux-mm@...ck.org,
 linux-doc@...r.kernel.org, kernel@...labora.com
Subject: Re: [PATCH v4 08/13] drm/v3d: Fix builds with
 CONFIG_TRANSPARENT_HUGEPAGE=n

On Wed, 15 Oct 2025 17:30:12 +0200
Loïc Molinari <loic.molinari@...labora.com> wrote:

> Don't declare "super_pages" on builds with CONFIG_TRANSPARENT_HUGEPAGE
> disabled to prevent build error:
> 
> ERROR: modpost: "super_pages" [drivers/gpu/drm/v3d/v3d.ko] undefined!

I believe this is a bug introduced by the previous commit: the
compiler probably drops any code between the
IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) check and the err label
because IS_ENABLED() evaluates to false at compile time. So I'd squash
those changes in the previous commit.

> 
> Signed-off-by: Loïc Molinari <loic.molinari@...labora.com>
> ---
>  drivers/gpu/drm/v3d/v3d_drv.h | 2 ++
>  drivers/gpu/drm/v3d/v3d_gem.c | 2 ++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/v3d/v3d_drv.h b/drivers/gpu/drm/v3d/v3d_drv.h
> index 99a39329bb85..481502104391 100644
> --- a/drivers/gpu/drm/v3d/v3d_drv.h
> +++ b/drivers/gpu/drm/v3d/v3d_drv.h
> @@ -564,7 +564,9 @@ extern const struct dma_fence_ops v3d_fence_ops;
>  struct dma_fence *v3d_fence_create(struct v3d_dev *v3d, enum v3d_queue q);
>  
>  /* v3d_gem.c */
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>  extern bool super_pages;
> +#endif
>  int v3d_gem_init(struct drm_device *dev);
>  void v3d_gem_destroy(struct drm_device *dev);
>  void v3d_reset_sms(struct v3d_dev *v3d);
> diff --git a/drivers/gpu/drm/v3d/v3d_gem.c b/drivers/gpu/drm/v3d/v3d_gem.c
> index 635ff0fabe7e..0039063eb8b2 100644
> --- a/drivers/gpu/drm/v3d/v3d_gem.c
> +++ b/drivers/gpu/drm/v3d/v3d_gem.c
> @@ -269,7 +269,9 @@ v3d_huge_mnt_init(struct v3d_dev *v3d)
>  	 * match our usecase.
>  	 */
>  
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>  	if (super_pages)
> +#endif
>  		err = drm_gem_huge_mnt_create(&v3d->drm, "within_size");

Why not

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
  	if (super_pages)
  		err = drm_gem_huge_mnt_create(&v3d->drm, "within_size");
#endif

I guess

	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && super_pages)
		err = drm_gem_huge_mnt_create(&v3d->drm, "within_size");

would also do, since it's likely to rely on the same optimization the
previous v3d_gemfs_init() implementation was relying on, but it's
fragile (not sure what happens when compiled with -O0).

>  
>  	if (v3d->drm.huge_mnt)