linux-kernel - Re: [PATCH] drm/i915: Handle null 'fb' in 'intel_plane_atomic_check_with

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Message-ID: <87h65trcqj.fsf@intel.com>
Date: Mon, 20 Jan 2025 12:39:00 +0200
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: Lu Yao <yaolu@...inos.cn>, rodrigo.vivi@...el.com,
 joonas.lahtinen@...ux.intel.com, tursulin@...ulin.net
Cc: intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, Lu Yao <yaolu@...inos.cn>
Subject: Re: [PATCH] drm/i915: Handle null 'fb' in
 'intel_plane_atomic_check_with_state'

On Mon, 20 Jan 2025, Lu Yao <yaolu@...inos.cn> wrote:
> Add null pointer check before use fb.
> Reported by smatch.

If new_plane_state->uapi.visible is true, fb will be non-NULL too, but
smatch is unable to see that.

Adding these checks makes one believe that this is not something you can
rely on.

BR,
Jani.

>
> Signed-off-by: Lu Yao <yaolu@...inos.cn>
> ---
>  drivers/gpu/drm/i915/display/intel_atomic_plane.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_atomic_plane.c b/drivers/gpu/drm/i915/display/intel_atomic_plane.c
> index d89630b2d5c1..20bfa9589ee7 100644
> --- a/drivers/gpu/drm/i915/display/intel_atomic_plane.c
> +++ b/drivers/gpu/drm/i915/display/intel_atomic_plane.c
> @@ -640,18 +640,18 @@ int intel_plane_atomic_check_with_state(const struct intel_crtc_state *old_crtc_
>  	    intel_plane_is_scaled(new_plane_state))
>  		new_crtc_state->scaled_planes |= BIT(plane->id);
>  
> -	if (new_plane_state->uapi.visible &&
> +	if (fb && new_plane_state->uapi.visible &&
>  	    intel_format_info_is_yuv_semiplanar(fb->format, fb->modifier))
>  		new_crtc_state->nv12_planes |= BIT(plane->id);
>  
> -	if (new_plane_state->uapi.visible &&
> +	if (fb && new_plane_state->uapi.visible &&
>  	    fb->format->format == DRM_FORMAT_C8)
>  		new_crtc_state->c8_planes |= BIT(plane->id);
>  
>  	if (new_plane_state->uapi.visible || old_plane_state->uapi.visible)
>  		new_crtc_state->update_planes |= BIT(plane->id);
>  
> -	if (new_plane_state->uapi.visible &&
> +	if (fb && new_plane_state->uapi.visible &&
>  	    intel_format_info_is_yuv_semiplanar(fb->format, fb->modifier)) {
>  		new_crtc_state->data_rate_y[plane->id] =
>  			intel_plane_data_rate(new_crtc_state, new_plane_state, 0);

-- 
Jani Nikula, Intel