[Intel-gfx] [PATCH 04/12] drm/i915: Don't unconditionally try to deref aliasing ppgtt

[Chris Wilson]

On Mon, Nov 25, 2013 at 09:54:35AM -0800, Ben Widawsky wrote:
> Since the beginning, the functions which try to properly reference the
> aliasing PPGTT have deferences a potentially null aliasing_ppgtt member.
> Since the accessors are meant to be global, this will not do.
> 
> Introduced originally in:
> commit a70a3148b0c61cb7c588ea650db785b261b378a3
> Author: Ben Widawsky <ben at bwidawsk.net>
> Date:   Wed Jul 31 16:59:56 2013 -0700
> 
>     drm/i915: Make proper functions for VMs
> 
> Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 40d9dcf..bc5c865 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -4971,7 +4971,8 @@ unsigned long i915_gem_obj_offset(struct drm_i915_gem_object *o,
>  	struct drm_i915_private *dev_priv = o->base.dev->dev_private;
>  	struct i915_vma *vma;
>  
> -	if (vm == &dev_priv->mm.aliasing_ppgtt->base)
> +	if (!dev_priv->mm.aliasing_ppgtt ||
> +	    vm == &dev_priv->mm.aliasing_ppgtt->base)

Where's the dereference? gcc is smarter than your average bear.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre