s390/ism: Do not unregister clients with registered DMBs

[ Upstream commit 266deee ]

When ism_unregister_client() is called but the client still has DMBs
registered it returns -EBUSY and prints an error. This only happens
after the client has already been unregistered however. This is
unexpected as the unregister claims to have failed. Furthermore as this
implies a client bug a WARN() is more appropriate. Thus move the
deregistration after the check and use WARN().

Fixes: 89e7d2b ("net/ism: Add new API for client registration")
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/s390/net/ism_drv.c

@@ -96,29 +96,32 @@ int ism_unregister_client(struct ism_client *client)
 	int rc = 0;
 
 	mutex_lock(&ism_dev_list.mutex);
-	mutex_lock(&clients_lock);
-	clients[client->id] = NULL;
-	if (client->id + 1 == max_client)
-		max_client--;
-	mutex_unlock(&clients_lock);
 	list_for_each_entry(ism, &ism_dev_list.list, list) {
 		spin_lock_irqsave(&ism->lock, flags);
 		/* Stop forwarding IRQs and events */
 		ism->subs[client->id] = NULL;
 		for (int i = 0; i < ISM_NR_DMBS; ++i) {
 			if (ism->sba_client_arr[i] == client->id) {
-				pr_err("%s: attempt to unregister client '%s'"
-				       "with registered dmb(s)\n", __func__,
-				       client->name);
+				WARN(1, "%s: attempt to unregister '%s' with registered dmb(s)\n",
+				     __func__, client->name);
 				rc = -EBUSY;
-				goto out;
+				goto err_reg_dmb;
 			}
 		}
 		spin_unlock_irqrestore(&ism->lock, flags);
 	}
-out:
 	mutex_unlock(&ism_dev_list.mutex);
 
+	mutex_lock(&clients_lock);
+	clients[client->id] = NULL;
+	if (client->id + 1 == max_client)
+		max_client--;
+	mutex_unlock(&clients_lock);
+	return rc;
+
+err_reg_dmb:
+	spin_unlock_irqrestore(&ism->lock, flags);
+	mutex_unlock(&ism_dev_list.mutex);
 	return rc;
 }
 EXPORT_SYMBOL_GPL(ism_unregister_client);