logging: fix tsan error
logging: fix tsan error

Summary:
See discussion on:
https://fb.workplace.com/groups/threadsanitizer/posts/618585969412291

Reviewed By: Skory

Differential Revision: D33458874

fbshipit-source-id: 47829a71c66c2f254796ad59efa1f58c94287412

facebook/mcrouter,facebook/mcrouter,facebook/mcrouter,facebook/mcrouter