I think we should cherry-pick 41e3efd07d5a02c80f503e29d755aa1bbb4245de
https://lore.kernel.org/patchwork/patch/856512/ into 4.14. It fixes a
potential resource leak when shutting down the request queue.
Once this patch is applied, there is a potential for a null pointer dereference.
That's what the second patch fixes.
The third patch is just an optimization to stop processing earlier.