io_uring/rw: treat -EOPNOTSUPP for IOCB_NOWAIT like -EAGAIN

Some file systems, ocfs2 in this case, will return -EOPNOTSUPP for
an IOCB_NOWAIT read/write attempt. While this can be argued to be
correct, the usual return value for something that requires blocking
issue is -EAGAIN.

A refactoring io_uring commit dropped calling kiocb_done() for
negative return values, which is otherwise where we already do that
transformation. To ensure we catch it in both spots, check it in
__io_read() itself as well.
Reported-by: Robert Sander <r.sander@heinlein-support.de>
Link: https://fosstodon.org/@gurubert@mastodon.gurubert.de/113112431889638440
Cc: stable@vger.kernel.org
Fixes: a08d195b ("io_uring/rw: split io_read() into a helper")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/rw.c

@@ -855,6 +855,14 @@ static int __io_read(struct io_kiocb *req, unsigned int issue_flags)
 
 	ret = io_iter_do_read(rw, &io->iter);
 
+	/*
+	 * Some file systems like to return -EOPNOTSUPP for an IOCB_NOWAIT
+	 * issue, even though they should be returning -EAGAIN. To be safe,
+	 * retry from blocking context for either.
+	 */
+	if (ret == -EOPNOTSUPP && force_nonblock)
+		ret = -EAGAIN;
+
 	if (ret == -EAGAIN || (req->flags & REQ_F_REISSUE)) {
 		req->flags &= ~REQ_F_REISSUE;
 		/* If we can poll, just do that. */