io_uring: honor IOSQE_ASYNC for linked reqs

mainline inclusion
from mainline-5.6-rc1
commit 86a761f8
category: feature
bugzilla: https://bugzilla.openeuler.org/show_bug.cgi?id=27
CVE: NA
---------------------------

REQ_F_FORCE_ASYNC is checked only for the head of a link. Fix it.
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: Nyangerkun <yangerkun@huawei.com>
Reviewed-by: Nzhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: NCheng Jian <cj.chengjian@huawei.com>

fs/io_uring.c

@@ -4454,6 +4454,7 @@ static void __io_queue_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	 */
 	if (ret == -EAGAIN && (!(req->flags & REQ_F_NOWAIT) ||
 	    (req->flags & REQ_F_MUST_PUNT))) {
+punt:
 		if (req->work.flags & IO_WQ_WORK_NEEDS_FILES) {
 			ret = io_grab_files(req);
 			if (ret)
@@ -4489,6 +4490,9 @@ static void __io_queue_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	if (nxt) {
 		req = nxt;
 		nxt = NULL;
+
+		if (req->flags & REQ_F_FORCE_ASYNC)
+			goto punt;
 		goto again;
 	}
 }