btrfs: merge back btrfs_read_lock_root_node helpers

We no longer have recursive locking and there's no need for separate
helpers that allowed the transition to rwsem with minimal code changes.
Reviewed-by: NFilipe Manana <fdmanana@suse.com>
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/ctree.c

@@ -2533,7 +2533,7 @@ static struct extent_buffer *btrfs_search_slot_get_root(struct btrfs_root *root,
 		 * We don't know the level of the root node until we actually
 		 * have it read locked
 		 */
-		b = __btrfs_read_lock_root_node(root, 0);
+		b = btrfs_read_lock_root_node(root);
 		level = btrfs_header_level(b);
 		if (level > write_lock_level)
 			goto out;

fs/btrfs/locking.c

@@ -184,14 +184,13 @@ struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root)
  *
  * Return: root extent buffer with read lock held
  */
-struct extent_buffer *__btrfs_read_lock_root_node(struct btrfs_root *root,
-						  bool recurse)
+struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root)
 {
 	struct extent_buffer *eb;
 
 	while (1) {
 		eb = btrfs_root_node(root);
-		__btrfs_tree_read_lock(eb, BTRFS_NESTING_NORMAL, recurse);
+		btrfs_tree_read_lock(eb);
 		if (eb == root->node)
 			break;
 		btrfs_tree_read_unlock(eb);

fs/btrfs/locking.h

@@ -94,13 +94,7 @@ void btrfs_tree_read_unlock(struct extent_buffer *eb);
 int btrfs_try_tree_read_lock(struct extent_buffer *eb);
 int btrfs_try_tree_write_lock(struct extent_buffer *eb);
 struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root);
-struct extent_buffer *__btrfs_read_lock_root_node(struct btrfs_root *root,
-						  bool recurse);
-
-static inline struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root)
-{
-	return __btrfs_read_lock_root_node(root, false);
-}
+struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root);
 
 #ifdef CONFIG_BTRFS_DEBUG
 static inline void btrfs_assert_tree_locked(struct extent_buffer *eb) {