drm/i915: Only clear the client pointer when tearing down the file

Upon release of the file (i.e. the user calls close(fd)), we decouple
all objects from the client list so that we don't chase the dangling
file_priv. As we always inspect file_priv first, we only need to nullify
that pointer and can safely ignore the list_head.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1469432687-22756-4-git-send-email-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1469530913-17180-3-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem.c

@@ -4745,21 +4745,15 @@ int i915_gem_freeze_late(struct drm_i915_private *dev_priv)
 void i915_gem_release(struct drm_device *dev, struct drm_file *file)
 {
 	struct drm_i915_file_private *file_priv = file->driver_priv;
+	struct drm_i915_gem_request *request;
 
 	/* Clean up our request list when the client is going away, so that
 	 * later retire_requests won't dereference our soon-to-be-gone
 	 * file_priv.
 	 */
 	spin_lock(&file_priv->mm.lock);
-	while (!list_empty(&file_priv->mm.request_list)) {
-		struct drm_i915_gem_request *request;
-
-		request = list_first_entry(&file_priv->mm.request_list,
-					   struct drm_i915_gem_request,
-					   client_list);
-		list_del(&request->client_list);
+	list_for_each_entry(request, &file_priv->mm.request_list, client_list)
 		request->file_priv = NULL;
-	}
 	spin_unlock(&file_priv->mm.lock);
 
 	if (!list_empty(&file_priv->rps.link)) {