Drivers: hv: vmbus: add an API vmbus_hvsock_device_unregister()

The hvsock driver needs this API to release all the resources related
to the channel.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 4a320e6..fa86b2c 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -288,7 +288,8 @@
 	struct list_head *cur, *tmp;
 	struct vmbus_channel *cur_sc;
 
-	mutex_lock(&vmbus_connection.channel_mutex);
+	BUG_ON(!mutex_is_locked(&vmbus_connection.channel_mutex));
+
 	list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) {
 		if (channel->offermsg.child_relid == relid) {
 			found_channel = channel;
@@ -307,7 +308,6 @@
 			}
 		}
 	}
-	mutex_unlock(&vmbus_connection.channel_mutex);
 
 	return found_channel;
 }