RDMA/addr: Use client registration to fix module unload race

Require registration with ib_addr module to prevent caller from
unloading while a callback is in progress.

Signed-off-by: Sean Hefty <[e-mail]>
Signed-off-by: Roland Dreier <[e-mail]>

drivers/infiniband/core/addr.c

···
 	struct sockaddr src_addr;
 	struct sockaddr dst_addr;
 	struct rdma_dev_addr *addr;
+	struct rdma_addr_client *client;
 	void *context;
 	void (*callback)(int status, struct sockaddr *src_addr,
 			 struct rdma_dev_addr *addr, void *context);
···
 static LIST_HEAD(req_list);
 static DECLARE_WORK(work, process_req, NULL);
 static struct workqueue_struct *addr_wq;
+
+void rdma_addr_register_client(struct rdma_addr_client *client)
+{
+	atomic_set(&client->refcount, 1);
+	init_completion(&client->comp);
+}
+EXPORT_SYMBOL(rdma_addr_register_client);
+
+static inline void put_client(struct rdma_addr_client *client)
+{
+	if (atomic_dec_and_test(&client->refcount))
+		complete(&client->comp);
+}
+
+void rdma_addr_unregister_client(struct rdma_addr_client *client)
+{
+	put_client(client);
+	wait_for_completion(&client->comp);
+}
+EXPORT_SYMBOL(rdma_addr_unregister_client);
 
 int rdma_copy_addr(struct rdma_dev_addr *dev_addr, struct net_device *dev,
 		     const unsigned char *dst_dev_addr)
···
 		list_del(&req->list);
 		req->callback(req->status, &req->src_addr, req->addr,
 			      req->context);
+		put_client(req->client);
 		kfree(req);
 	}
 }
···
 	return ret;
 }
 
-int rdma_resolve_ip(struct sockaddr *src_addr, struct sockaddr *dst_addr,
+int rdma_resolve_ip(struct rdma_addr_client *client,
+		    struct sockaddr *src_addr, struct sockaddr *dst_addr,
 		    struct rdma_dev_addr *addr, int timeout_ms,
 		    void (*callback)(int status, struct sockaddr *src_addr,
 				     struct rdma_dev_addr *addr, void *context),
···
 	req->addr = addr;
 	req->callback = callback;
 	req->context = context;
+	req->client = client;
+	atomic_inc(&client->refcount);
 
 	src_in = (struct sockaddr_in *) &req->src_addr;
 	dst_in = (struct sockaddr_in *) &req->dst_addr;
···
 		break;
 	default:
 		ret = req->status;
+		atomic_dec(&client->refcount);
 		kfree(req);
 		break;
 	}

drivers/infiniband/core/cma.c

···
 };
 
 static struct ib_sa_client sa_client;
+static struct rdma_addr_client addr_client;
 static LIST_HEAD(dev_list);
 static LIST_HEAD(listen_any_list);
 static DEFINE_MUTEX(lock);
···
 	if (cma_any_addr(dst_addr))
 		ret = cma_resolve_loopback(id_priv);
 	else
-		ret = rdma_resolve_ip(&id->route.addr.src_addr, dst_addr,
-				      &id->route.addr.dev_addr,
+		ret = rdma_resolve_ip(&addr_client, &id->route.addr.src_addr,
+				      dst_addr, &id->route.addr.dev_addr,
 				      timeout_ms, addr_handler, id_priv);
 	if (ret)
 		goto err;
···
 		return -ENOMEM;
 
 	ib_sa_register_client(&sa_client);
+	rdma_addr_register_client(&addr_client);
 
 	ret = ib_register_client(&cma_client);
 	if (ret)
···
 	return 0;
 
 err:
+	rdma_addr_unregister_client(&addr_client);
 	ib_sa_unregister_client(&sa_client);
 	destroy_workqueue(cma_wq);
 	return ret;
···
 static void cma_cleanup(void)
 {
 	ib_unregister_client(&cma_client);
+	rdma_addr_unregister_client(&addr_client);
 	ib_sa_unregister_client(&sa_client);
 	destroy_workqueue(cma_wq);
 	idr_destroy(&sdp_ps);

include/rdma/ib_addr.h

···
 #include <linux/socket.h>
 #include <rdma/ib_verbs.h>
 
+struct rdma_addr_client {
+	atomic_t refcount;
+	struct completion comp;
+};
+
+/**
+ * rdma_addr_register_client - Register an address client.
+ */
+void rdma_addr_register_client(struct rdma_addr_client *client);
+
+/**
+ * rdma_addr_unregister_client - Deregister an address client.
+ * @client: Client object to deregister.
+ */
+void rdma_addr_unregister_client(struct rdma_addr_client *client);
+
 struct rdma_dev_addr {
 	unsigned char src_dev_addr[MAX_ADDR_LEN];
 	unsigned char dst_dev_addr[MAX_ADDR_LEN];
···
 /**
  * rdma_resolve_ip - Resolve source and destination IP addresses to
  *   RDMA hardware addresses.
+ * @client: Address client associated with request.
  * @src_addr: An optional source address to use in the resolution.  If a
  *   source address is not provided, a usable address will be returned via
  *   the callback.
···
  *   or been canceled.  A status of 0 indicates success.
  * @context: User-specified context associated with the call.
  */
-int rdma_resolve_ip(struct sockaddr *src_addr, struct sockaddr *dst_addr,
+int rdma_resolve_ip(struct rdma_addr_client *client,
+		    struct sockaddr *src_addr, struct sockaddr *dst_addr,
 		    struct rdma_dev_addr *addr, int timeout_ms,
 		    void (*callback)(int status, struct sockaddr *src_addr,
 				     struct rdma_dev_addr *addr, void *context),