btrfs: use radix_tree_iter_retry()

Even though this is a 'can't happen' situation, use the new
radix_tree_iter_retry() pattern to eliminate a goto.

[akpm@linux-foundation.org: fix btrfs build]
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <jbacik@fb.com>
Cc: David Sterba <dsterba@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/btrfs/tests/btrfs-tests.c

@@ -137,7 +137,6 @@ static void btrfs_free_dummy_fs_info(struct btrfs_fs_info *fs_info)
 	void **slot;
 
 	spin_lock(&fs_info->buffer_lock);
-restart:
 	radix_tree_for_each_slot(slot, &fs_info->buffer_radix, &iter, 0) {
 		struct extent_buffer *eb;
 
@@ -147,7 +146,7 @@ static void btrfs_free_dummy_fs_info(struct btrfs_fs_info *fs_info)
 		/* Shouldn't happen but that kind of thinking creates CVE's */
 		if (radix_tree_exception(eb)) {
 			if (radix_tree_deref_retry(eb))
-				goto restart;
+				slot = radix_tree_iter_retry(&iter);
 			continue;
 		}
 		spin_unlock(&fs_info->buffer_lock);