RDMA/device: Provide APIs from the core code to help unregistration

These APIs are intended to support drivers that exist outside the usual
driver core probe()/remove() callbacks. Normally the driver core will
prevent remove() from running concurrently with probe(), once this safety
is lost drivers need more support to get the locking and lifetimes right.

ib_unregister_driver() is intended to be used during module_exit of a
driver using these APIs. It unregisters all the associated ib_devices.

ib_unregister_device_and_put() is to be used by a driver-specific removal
function (ie removal by name, removal from a netdev notifier, removal from
netlink)

ib_unregister_queued() is to be used from netdev notifier chains where
RTNL is held.

The locking is tricky here since once things become async it is possible
to race unregister with registration. This is largely solved by relying on
the registration refcount, unregistration will only ever work on something
that has a positive registration refcount - and then an unregistration
mutex serializes all competing unregistrations of the same device.
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

include/rdma/ib_verbs.h

@@ -2538,6 +2538,12 @@ struct ib_device_ops {
 	int (*fill_res_entry)(struct sk_buff *msg,
 			      struct rdma_restrack_entry *entry);
 
+	/* Device lifecycle callbacks */
+	/*
+	 * This is called as part of ib_dealloc_device().
+	 */
+	void (*dealloc_driver)(struct ib_device *dev);
+
 	DECLARE_RDMA_OBJ_SIZE(ib_pd);
 };
 
@@ -2555,6 +2561,7 @@ struct ib_device {
 
 	struct rw_semaphore	      client_data_rwsem;
 	struct xarray                 client_data;
+	struct mutex                  unregistration_lock;
 
 	struct ib_cache               cache;
 	/**
@@ -2609,6 +2616,7 @@ struct ib_device {
 	 */
 	refcount_t refcount;
 	struct completion unreg_completion;
+	struct work_struct unregistration_work;
 };
 
 struct ib_client {
@@ -2658,6 +2666,9 @@ void ib_get_device_fw_str(struct ib_device *device, char *str);
 
 int ib_register_device(struct ib_device *device, const char *name);
 void ib_unregister_device(struct ib_device *device);
+void ib_unregister_driver(enum rdma_driver_id driver_id);
+void ib_unregister_device_and_put(struct ib_device *device);
+void ib_unregister_device_queued(struct ib_device *ib_dev);
 
 int ib_register_client   (struct ib_client *client);
 void ib_unregister_client(struct ib_client *client);