drm/i915/gem: Retire directly for mmap-offset shrinking

Now that we can retire without taking struct_mutex, we can do so to
handle shrinking the mmap-offset space after an allocation failure.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191004134015.13204-11-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/i915_gem_mman.c

@@ -431,19 +431,12 @@ static int create_mmap_offset(struct drm_i915_gem_object *obj)
 		return 0;
 
 	/* Attempt to reap some mmap space from dead objects */
-	do {
-		err = i915_gem_wait_for_idle(i915, MAX_SCHEDULE_TIMEOUT);
+	err = i915_retire_requests_timeout(i915, MAX_SCHEDULE_TIMEOUT);
 	if (err)
-			break;
+		return err;
 
 	i915_gem_drain_freed_objects(i915);
-		err = drm_gem_create_mmap_offset(&obj->base);
-		if (!err)
-			break;
-
-	} while (flush_delayed_work(&i915->gem.retire_work));
-
-	return err;
+	return drm_gem_create_mmap_offset(&obj->base);
 }
 
 int