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/relocation.c b/fs/btrfs/relocation.c
index ab7ab5318745..0109e5606bad 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -170,14 +170,14 @@ struct async_merge {
 
 static void mapping_tree_init(struct mapping_tree *tree)
 {
-        tree->rb_root.rb_node = NULL;
+        tree->rb_root = RB_ROOT;
         spin_lock_init(&tree->lock);
 }
 
 static void backref_cache_init(struct backref_cache *cache)
 {
         int i;
-        cache->rb_root.rb_node = NULL;
+        cache->rb_root = RB_ROOT;
         for (i = 0; i < BTRFS_MAX_LEVEL; i++)
                 INIT_LIST_HEAD(&cache->pending[i]);
         spin_lock_init(&cache->lock);