linux-kernel - Re: [PATCH next] drm/sysfb: Fix a NULL vs IS

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Message-ID: <aPJrs7_u8KcalNsC@intel.com>
Date: Fri, 17 Oct 2025 19:15:47 +0300
From: Ville Syrjälä <ville.syrjala@...ux.intel.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Thomas Zimmermann <tzimmermann@...e.de>,
	Javier Martinez Canillas <javierm@...hat.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH next] drm/sysfb: Fix a NULL vs IS_ERR() bug

On Fri, Oct 17, 2025 at 07:03:33PM +0300, Dan Carpenter wrote:
> The drm_atomic_get_crtc_state() function never returns NULL, it returns
> error pointers.  Update the error checking to match.
> 
> Fixes: cb71de092553 ("drm/sysfb: Lookup blit function during atomic check")
> Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> ---
>  drivers/gpu/drm/sysfb/drm_sysfb_modeset.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/sysfb/drm_sysfb_modeset.c b/drivers/gpu/drm/sysfb/drm_sysfb_modeset.c
> index 8517c490e815..d2c4d8f3d4d0 100644
> --- a/drivers/gpu/drm/sysfb/drm_sysfb_modeset.c
> +++ b/drivers/gpu/drm/sysfb/drm_sysfb_modeset.c
> @@ -259,7 +259,7 @@ int drm_sysfb_plane_helper_begin_fb_access(struct drm_plane *plane,
>  	ret = -EINVAL;
>  
>  	crtc_state = drm_atomic_get_crtc_state(plane_state->state, plane_state->crtc);

Looking at where this gets called, that should be
drm_atomic_get_new_crtc_state(). Either that or the
code is more seriously borked.

I'll send out a patch that warns about invalid use of 
*_get_state()...

> -	if (drm_WARN_ON_ONCE(dev, !crtc_state))
> +	if (drm_WARN_ON_ONCE(dev, IS_ERR(crtc_state)))
>  		goto err_drm_gem_end_shadow_fb_access;
>  	sysfb_crtc_state = to_drm_sysfb_crtc_state(crtc_state);
>  
> -- 
> 2.51.0

-- 
Ville Syrjälä
Intel