linux-kernel - Re: [PATCH] drm/vkms: fix variable dereferenced before check warning

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Date:   Sat, 10 Sep 2022 18:14:45 -0100
From:   Melissa Wen <mwen@...lia.com>
To:     Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
Cc:     Haneen Mohammed <hamohammed.sa@...il.com>,
        Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>,
        David Airlie <airlied@...ux.ie>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Melissa Wen <melissa.srw@...il.com>, dan.carpenter@...cle.com,
        Igor Torrente <igormtorrente@...il.com>
Subject: Re: [PATCH] drm/vkms: fix variable dereferenced before check warning

On 09/08, Harshit Mogalapalli wrote:
> Smatch warns:
> 
> drivers/gpu/drm/vkms/vkms_plane.c:110 vkms_plane_atomic_update() warn:
>  variable dereferenced before check 'fb' (see line 108)
> 
> Fix the warning by moving the dereference after the NULL check.
> 
> Fixes: 8ba1648567e2 ("drm: vkms: Refactor the plane composer to accept new formats")
> Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
> ---
>  drivers/gpu/drm/vkms/vkms_plane.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/vkms/vkms_plane.c b/drivers/gpu/drm/vkms/vkms_plane.c
> index f4319066adcc..c3a845220e10 100644
> --- a/drivers/gpu/drm/vkms/vkms_plane.c
> +++ b/drivers/gpu/drm/vkms/vkms_plane.c
> @@ -105,11 +105,12 @@ static void vkms_plane_atomic_update(struct drm_plane *plane,
>  	struct drm_shadow_plane_state *shadow_plane_state;
>  	struct drm_framebuffer *fb = new_state->fb;
>  	struct vkms_frame_info *frame_info;
> -	u32 fmt = fb->format->format;
> +	u32 fmt;
>  
>  	if (!new_state->crtc || !fb)
>  		return;
>  
> +	fmt = fb->format->format;

Hi Harshit,

Nice catch.

Thanks,

Reviewed-by: Melissa Wen <mwen@...lia.com>

>  	vkms_plane_state = to_vkms_plane_state(new_state);
>  	shadow_plane_state = &vkms_plane_state->base;
>  
> -- 
> 2.31.1
> 


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