drm/i915/region: don't leak the object on error

Sanity check the object size before allocating a new gem object.

Fixes: 97d5539 ("drm/i915/region: convert object_create into object_init")
Testcase: igt/gem_create/create-massive
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20210120104714.112812-1-matthew.auld@intel.com

drivers/gpu/drm/i915/gem/i915_gem_region.c

@@ -161,10 +161,6 @@ i915_gem_object_create_region(struct intel_memory_region *mem,
 	GEM_BUG_ON(!size);
 	GEM_BUG_ON(!IS_ALIGNED(size, I915_GTT_MIN_ALIGNMENT));
 
-	obj = i915_gem_object_alloc();
-	if (!obj)
-		return ERR_PTR(-ENOMEM);
-
 	/*
 	 * XXX: There is a prevalence of the assumption that we fit the
 	 * object's page count inside a 32bit _signed_ variable. Let's document
@@ -178,6 +174,10 @@ i915_gem_object_create_region(struct intel_memory_region *mem,
 	if (overflows_type(size, obj->base.size))
 		return ERR_PTR(-E2BIG);
 
+	obj = i915_gem_object_alloc();
+	if (!obj)
+		return ERR_PTR(-ENOMEM);
+
 	err = mem->ops->init_object(mem, obj, size, flags);
 	if (err)
 		goto err_object_free;