io_uring: fix lost getsockopt completions

There is a report that iowq executed getsockopt never completes. The
reason being that io_uring_cmd_sock() can return a positive result, and
io_uring_cmd() propagates it back to core io_uring, instead of IOU_OK.
In case of io_wq_submit_work(), the request will be dropped without
completing it.

The offending code was introduced by a hack in
a9c3eda ("io_uring: fix submission-failure handling for uring-cmd"),
however it was fine until getsockopt was introduced and started
returning positive results.

The right solution is to always return IOU_OK, since
e0b23d9 ("io_uring: optimise ltimeout for inline execution"),
we should be able to do it without problems, however for the sake of
backporting and minimising side effects, let's keep returning negative
return codes and otherwise do IOU_OK.

Link: https://github.com/axboe/liburing/issues/1181
Cc: stable@vger.kernel.org
Fixes: 8e9fad0 ("io_uring: Add io_uring command support for sockets")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Breno Leitao <leitao@debian.org>
Link: https://lore.kernel.org/r/ff349cf0654018189b6077e85feed935f0f8839e.1721149870.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/uring_cmd.c

@@ -265,7 +265,7 @@ int io_uring_cmd(struct io_kiocb *req, unsigned int issue_flags)
 		req_set_fail(req);
 	io_req_uring_cleanup(req, issue_flags);
 	io_req_set_res(req, ret, 0);
-	return ret;
+	return ret < 0 ? ret : IOU_OK;
 }
 
 int io_uring_cmd_import_fixed(u64 ubuf, unsigned long len, int rw,