io_uring: fix short read retries for non-reg files

io_uring: fix short read retries for non-reg files

commit 9a173346bd9e16ab19c7addb8862d95a5cea9feb upstream.

Sockets and other non-regular files may actually expect short reads to
happen, don't retry reads for them. Because non-reg files don't set
FMODE_BUF_RASYNC and so it won't do second/retry do_read, we can filter
out those cases after first do_read() attempt with ret>0.

Cc: stable@vger.kernel.org # 5.9+
Suggested-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>