io_uring: remove unnecessary PF_EXITING check

We prefer nornal task_works even if it would fail requests inside. Kill
a PF_EXITING check in io_req_task_work_add(), task_work_add() handles
well dying tasks, i.e. return error when can't enqueue due to late
stages of do_exit().
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/fc14297e8441cd8f5d1743a2488cf0df09bf48ac.1628471125.git.asml.silence@gmail.comSigned-off-by: NJens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -2006,8 +2006,6 @@ static void io_req_task_work_add(struct io_kiocb *req)
 	if (test_bit(0, &tctx->task_state) ||
 	    test_and_set_bit(0, &tctx->task_state))
 		return;
-	if (unlikely(tsk->flags & PF_EXITING))
-		goto fail;
 
 	/*
 	 * SQPOLL kernel thread doesn't need notification, just a wakeup. For
@@ -2020,7 +2018,7 @@ static void io_req_task_work_add(struct io_kiocb *req)
 		wake_up_process(tsk);
 		return;
 	}
-fail:
+
 	clear_bit(0, &tctx->task_state);
 	spin_lock_irqsave(&tctx->task_lock, flags);
 	node = tctx->task_list.first;