io_uring: store add. return values for CQE32

This reuses the hash list node for the storage we need to hold the two
64-bit values that must be passed back.

Co-developed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Stefan Roesch <shr@fb.com>
Reviewed-by: Kanchan Joshi <joshi.k@samsung.com>
Link: https://lore.kernel.org/r/20220426182134.136504-3-shr@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -1003,7 +1003,13 @@ struct io_kiocb {
 	atomic_t			poll_refs;
 	struct io_task_work		io_task_work;
 	/* for polled requests, i.e. IORING_OP_POLL_ADD and async armed poll */
-	struct hlist_node		hash_node;
+	union {
+		struct hlist_node	hash_node;
+		struct {
+			u64		extra1;
+			u64		extra2;
+		};
+	};
 	/* internal polling, see IORING_FEAT_FAST_POLL */
 	struct async_poll		*apoll;
 	/* opcode allocated if it needs to store data for async defer */