Re: [PATCH] drm/i915: Reorder phys backing storage release

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

On ke, 2016-12-07 at 10:07 +0000, Chris Wilson wrote:
> In commit a4f5ea64f0a8 ("drm/i915: Refactor object page API"), I
> reordered the object->pages teardown to be more friendly wrt to a
> separate obj->mm.lock. However, I overlooked the phys object and left it
> with a dangling use-after-free of its phys_handle. Move the allocation
> of the phys handle to get_pages and it release to put_pages to prevent
> the invalid access and to improve symmetry.
> 
> Testcase: igt/drv_selftest/objects
> Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Fixes: a4f5ea64f0a8 ("drm/i915: Refactor object page API")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: intel-gfx@lists.freedesktop.org

<SNIP>

>  i915_gem_object_get_pages_phys(struct drm_i915_gem_object *obj)
>  {
>  	struct address_space *mapping = obj->base.filp->f_mapping;
> -	char *vaddr = obj->phys_handle->vaddr;
> +	drm_dma_handle_t *phys;
>  	struct sg_table *st;
>  	struct scatterlist *sg;
> +	char *vaddr;
>  	int i;
>  
>  	if (WARN_ON(i915_gem_object_needs_bit17_swizzle(obj)))
>  		return ERR_PTR(-EINVAL);
>  
> +	phys = drm_pci_alloc(obj->base.dev, obj->base.size, obj->base.size);

Aligning to object size sounds bit rough without any comments.

> @@ -204,21 +212,29 @@ i915_gem_object_get_pages_phys(struct drm_i915_gem_object *obj)
>  	i915_gem_chipset_flush(to_i915(obj->base.dev));
>  
>  	st = kmalloc(sizeof(*st), GFP_KERNEL);
> -	if (st == NULL)
> -		return ERR_PTR(-ENOMEM);
> +	if (st == NULL) {

Could convert to (!st) when touching, pleases checkpatch.pl.

With the align propagated or explained in a comment;

Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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