drm/i915: Be more careful when unbinding vma

When we call i915_vma_unbind(), we will wait upon outstanding rendering.
This will also trigger a retirement phase, which may update the object
lists. If, we extend request tracking to the VMA itself (rather than
keep it at the encompassing object), then there is a potential that the
obj->vma_list be modified for other elements upon i915_vma_unbind(). As
a result, if we walk over the object list and call i915_vma_unbind(), we
need to be prepared for that list to change.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1470293567-10811-8-git-send-email-chris@chris-wilson.co.uk
diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index ca8b82a..e935b32 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -104,7 +104,6 @@
 
 	if (obj->pages != NULL) {
 		struct drm_i915_private *dev_priv = to_i915(dev);
-		struct i915_vma *vma, *tmp;
 		bool was_interruptible;
 
 		wait_rendering(obj);
@@ -112,8 +111,7 @@
 		was_interruptible = dev_priv->mm.interruptible;
 		dev_priv->mm.interruptible = false;
 
-		list_for_each_entry_safe(vma, tmp, &obj->vma_list, obj_link)
-			WARN_ON(i915_vma_unbind(vma));
+		WARN_ON(i915_gem_object_unbind(obj));
 		WARN_ON(i915_gem_object_put_pages(obj));
 
 		dev_priv->mm.interruptible = was_interruptible;