drm/i915: Assert no external observers when unwind a failed request alloc

Before we return the request back to the kmem_cache after a failed
i915_gem_request_alloc(), we should assert that it has not been added to
any global state tracking.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161125131718.20978-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_request.c

@@ -599,6 +599,11 @@ i915_gem_request_alloc(struct intel_engine_cs *engine,
 	return req;
 
 err_ctx:
+	/* Make sure we didn't add ourselves to external state before freeing */
+	GEM_BUG_ON(!list_empty(&req->active_list));
+	GEM_BUG_ON(!list_empty(&req->priotree.signalers_list));
+	GEM_BUG_ON(!list_empty(&req->priotree.waiters_list));
+
 	i915_gem_context_put(ctx);
 	kmem_cache_free(dev_priv->requests, req);
 err_unreserve: