io_uring: treat -EAGAIN for REQ_F_NOWAIT as final for io-wq

io-wq assumes that an issue is blocking, but it may not be if the
request type has asked for a non-blocking attempt. If we get
-EAGAIN for that case, then we need to treat it as a final result
and not retry or arm poll for it.

Cc: stable@vger.kernel.org # 5.10+
Link: https://github.com/axboe/liburing/issues/897
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/io_uring.c

@@ -1948,6 +1948,14 @@ void io_wq_submit_work(struct io_wq_work *work)
 		ret = io_issue_sqe(req, issue_flags);
 		if (ret != -EAGAIN)
 			break;
+
+		/*
+		 * If REQ_F_NOWAIT is set, then don't wait or retry with
+		 * poll. -EAGAIN is final for that case.
+		 */
+		if (req->flags & REQ_F_NOWAIT)
+			break;
+
 		/*
 		 * We can get EAGAIN for iopolled IO even though we're
 		 * forcing a sync submission from here, since we can't