io_uring: short circuit -EAGAIN for blocking read attempt

One case was missed in the short IO retry handling, and that's hitting
-EAGAIN on a blocking attempt read (eg from io-wq context). This is a
problem on sockets that are marked as non-blocking when created, they
don't carry any REQ_F_NOWAIT information to help us terminate them
instead of perpetually retrying.

Fixes: 227c0c96 ("io_uring: internally retry short reads")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -3186,6 +3186,8 @@ static int io_read(struct io_kiocb *req, bool force_nonblock,
 		ret = 0;
 		goto out_free;
 	} else if (ret == -EAGAIN) {
+		if (!force_nonblock)
+			goto done;
 		ret = io_setup_async_rw(req, iovec, inline_vecs, iter, false);
 		if (ret)
 			goto out_free;
@@ -3195,7 +3197,8 @@ static int io_read(struct io_kiocb *req, bool force_nonblock,
 	}
 
 	/* read it all, or we did blocking attempt. no retry. */
-	if (!iov_iter_count(iter) || !force_nonblock)
+	if (!iov_iter_count(iter) || !force_nonblock ||
+	    (req->file->f_flags & O_NONBLOCK))
 		goto done;
 
 	io_size -= ret;