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, 1 insertions, 1 deletions

diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
index 5a4f73b79b75..5a01f35507dd 100644
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -35,7 +35,7 @@ void extent_map_exit(void)
  */
 void extent_map_tree_init(struct extent_map_tree *tree, gfp_t mask)
 {
-        tree->map.rb_node = NULL;
+        tree->map = RB_ROOT;
         rwlock_init(&tree->lock);
 }