io-wq: cancel work if we fail getting a mm reference

If we require mm and user context, mark the request for cancellation
if we fail to acquire the desired mm.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io-wq.c

@@ -445,10 +445,14 @@ static void io_worker_handle_work(struct io_worker *worker)
 			task_unlock(current);
 		}
 		if ((work->flags & IO_WQ_WORK_NEEDS_USER) && !worker->mm &&
-		    wq->mm && mmget_not_zero(wq->mm)) {
+		    wq->mm) {
+			if (mmget_not_zero(wq->mm)) {
 				use_mm(wq->mm);
 				set_fs(USER_DS);
 				worker->mm = wq->mm;
+			} else {
+				work->flags |= IO_WQ_WORK_CANCEL;
+			}
 		}
 		if (!worker->creds)
 			worker->creds = override_creds(wq->creds);