RDMA/devices: Use xarray to store the client_data

Now that we have a small ID for each client we can use xarray instead of
linearly searching linked lists for client data. This will give much
faster and scalable client data lookup, and will lets us revise the
locking scheme.

Since xarray can store 'going_down' using a mark just entirely eliminate
the struct ib_client_data and directly store the client_data value in the
xarray. However this does require a special iterator as we must still
iterate over any NULL client_data values.

Also eliminate the client_data_lock in favour of internal xarray locking.
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

include/rdma/ib_verbs.h

@@ -2542,12 +2542,7 @@ struct ib_device {
 	struct list_head              event_handler_list;
 	spinlock_t                    event_handler_lock;
 
-	rwlock_t			client_data_lock;
-	struct list_head              core_list;
-	/* Access to the client_data_list is protected by the client_data_lock
-	 * rwlock and the lists_rwsem read-write semaphore
-	 */
-	struct list_head              client_data_list;
+	struct xarray                 client_data;
 
 	struct ib_cache               cache;
 	/**
@@ -2660,7 +2655,21 @@ void ib_unregister_device(struct ib_device *device);
 int ib_register_client   (struct ib_client *client);
 void ib_unregister_client(struct ib_client *client);
 
-void *ib_get_client_data(struct ib_device *device, struct ib_client *client);
+/**
+ * ib_get_client_data - Get IB client context
+ * @device:Device to get context for
+ * @client:Client to get context for
+ *
+ * ib_get_client_data() returns the client context data set with
+ * ib_set_client_data(). This can only be called while the client is
+ * registered to the device, once the ib_client remove() callback returns this
+ * cannot be called.
+ */
+static inline void *ib_get_client_data(struct ib_device *device,
+				       struct ib_client *client)
+{
+	return xa_load(&device->client_data, client->client_id);
+}
 void  ib_set_client_data(struct ib_device *device, struct ib_client *client,
 			 void *data);
 void ib_set_device_ops(struct ib_device *device,