Btrfs: use RB_ROOT to intialize rb_trees instead of setting rb_node to NULL

btrfs inialize rb trees in quite a number of places by settin rb_node =
NULL;  The problem with this is that 17d9ddc72fb8bba0d4f678 in the
linux-next tree adds a new field to that struct which needs to be NULL for
the new rbtree library code to work properly.  This patch uses RB_ROOT as
the intializer so all of the relevant fields will be NULL'd.  Without the
patch I get a panic.

Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index cb2849f03251..dd831ed31eea 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -870,7 +870,7 @@ __btrfs_return_cluster_to_free_space(
                 tree_insert_offset(&block_group->free_space_offset,
                                    entry->offset, &entry->offset_index, 0);
         }
-        cluster->root.rb_node = NULL;
+        cluster->root = RB_ROOT;
 
 out:
         spin_unlock(&cluster->lock);
@@ -1355,7 +1355,7 @@ void btrfs_init_free_cluster(struct btrfs_free_cluster *cluster)
 {
         spin_lock_init(&cluster->lock);
         spin_lock_init(&cluster->refill_lock);
-        cluster->root.rb_node = NULL;
+        cluster->root = RB_ROOT;
         cluster->max_size = 0;
         cluster->points_to_bitmap = false;
         INIT_LIST_HEAD(&cluster->block_group_list);