io-wq: don't ask for a new worker if we're exiting

If we're in the process of shutting down the async context, then don't
create new workers if we already have at least the fixed one.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io-wq.c

@@ -673,6 +673,8 @@ static inline bool io_wqe_need_worker(struct io_wqe *wqe, int index)
 {
 	struct io_wqe_acct *acct = &wqe->acct[index];
 
+	if (acct->nr_workers && test_bit(IO_WQ_BIT_EXIT, &wqe->wq->state))
+		return false;
 	/* if we have available workers or no work, no need */
 	if (!hlist_nulls_empty(&wqe->free_list) || !io_wqe_run_queue(wqe))
 		return false;