linux-kernel - Re: [PATCH 4/7] drivers/gpu/drm: remove invalid reference to list iterator variable

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Date:	Sun, 08 Jul 2012 22:52:25 +0200
From:	Paul Menzel <paulepanter@...rs.sourceforge.net>
To:	Julia Lawall <Julia.Lawall@...6.fr>
Cc:	David Airlie <airlied@...ux.ie>, kernel-janitors@...r.kernel.org,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 4/7] drivers/gpu/drm: remove invalid reference to list
 iterator variable

Dear Julia,


Am Sonntag, den 08.07.2012, 13:37 +0200 schrieb Julia Lawall:
> From: Julia Lawall <Julia.Lawall@...6.fr>
> 
> If list_for_each_entry, etc complete a traversal of the list, the iterator
> variable ends up pointing to an address at an offset from the list head,
> and not a meaningful structure.  Thus this value should not be used after
> the end of the iterator.
> 
> In the first two cases, a a break is added after the switch; the break in

s,a a,a,

> the switch would jump out of the switch, but not out of the complete
> iteration.
> 
> In the first case, the null test on connector is removed, because the
> iterator variable of list_for_each_entry is never null.
> 
> In the third case, entry->base.crtc.fb is not a meaningful value.  What
> seems to be intended is crtc->fb, which gets the information from the last
> element of the list.

maybe three separate patches would have been better?

> These problems were found using Coccinelle (http://coccinelle.lip6.fr/).

I always liked your example Coccinelle code snippets. Could you add them
again to your commit messages? That would be awesome!

> Signed-off-by: Julia Lawall <Julia.Lawall@...6.fr>
> 
> ---
>  drivers/gpu/drm/gma500/mdfld_intel_display.c |    4 +---
>  drivers/gpu/drm/gma500/oaktrail_crtc.c       |    1 +
>  drivers/gpu/drm/vmwgfx/vmwgfx_ldu.c          |    2 +-
>  3 files changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/gma500/mdfld_intel_display.c b/drivers/gpu/drm/gma500/mdfld_intel_display.c
> index 3f3cd61..fc1ced0 100644
> --- a/drivers/gpu/drm/gma500/mdfld_intel_display.c
> +++ b/drivers/gpu/drm/gma500/mdfld_intel_display.c
> @@ -755,9 +755,6 @@ static int mdfld_crtc_mode_set(struct drm_crtc *crtc,
>  					sizeof(struct drm_display_mode));
>  
>  	list_for_each_entry(connector, &mode_config->connector_list, head) {
> -		if (!connector)
> -			continue;
> -
>  		encoder = connector->encoder;
>  
>  		if (!encoder)
> @@ -779,6 +776,7 @@ static int mdfld_crtc_mode_set(struct drm_crtc *crtc,
>  			is_hdmi = true;
>  			break;
>  		}
> +		break;
>  	}
>  
>  	/* Disable the VGA plane that we never use */
> diff --git a/drivers/gpu/drm/gma500/oaktrail_crtc.c b/drivers/gpu/drm/gma500/oaktrail_crtc.c
> index f821c83..4b2172e 100644
> --- a/drivers/gpu/drm/gma500/oaktrail_crtc.c
> +++ b/drivers/gpu/drm/gma500/oaktrail_crtc.c
> @@ -329,6 +329,7 @@ static int oaktrail_crtc_mode_set(struct drm_crtc *crtc,
>  			is_mipi = true;
>  			break;
>  		}
> +		break;
>  	}
>  
>  	/* Disable the VGA plane that we never use */
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_ldu.c b/drivers/gpu/drm/vmwgfx/vmwgfx_ldu.c
> index 070fb23..634611a 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_ldu.c
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_ldu.c
> @@ -93,7 +93,7 @@ static int vmw_ldu_commit_list(struct vmw_private *dev_priv)
>  
>  		if (crtc == NULL)
>  			return 0;
> -		fb = entry->base.crtc.fb;
> +		fb = crtc->fb;
>  
>  		return vmw_kms_write_svga(dev_priv, w, h, fb->pitches[0],
>  					  fb->bits_per_pixel, fb->depth);

Acked-by: Paul Menzel <paulepanter@...rs.sourceforge.net>


Thanks,

Paul

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