Btrfs: make sure to recheck for bitmaps in clusters

Josef recently changed the free extent cache to look in
the block group cluster for any bitmaps before trying to
add a new bitmap for the same offset.  This avoids BUG_ON()s due
covering duplicate ranges.

But it didn't go quite far enough.  A given free range might span
between one or more bitmaps or free space entries.  The code has
looping to cover this, but it doesn't check for clustered bitmaps
every time.

This shuffles our gotos to check for a bitmap in the cluster
for every new bitmap entry we try to add.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/free-space-cache.c

@@ -1492,7 +1492,7 @@ static int insert_into_bitmap(struct btrfs_free_space_ctl *ctl,
 
 	if (ctl->op == &free_space_op)
 		block_group = ctl->private;
-
+again:
 	/*
 	 * Since we link bitmaps right into the cluster we need to see if we
 	 * have a cluster here, and if so and it has our bitmap we need to add
@@ -1510,13 +1510,13 @@ static int insert_into_bitmap(struct btrfs_free_space_ctl *ctl,
 		node = rb_first(&cluster->root);
 		if (!node) {
 			spin_unlock(&cluster->lock);
-			goto again;
+			goto no_cluster_bitmap;
 		}
 
 		entry = rb_entry(node, struct btrfs_free_space, offset_index);
 		if (!entry->bitmap) {
 			spin_unlock(&cluster->lock);
-			goto again;
+			goto no_cluster_bitmap;
 		}
 
 		if (entry->offset == offset_to_bitmap(ctl, offset)) {
@@ -1531,7 +1531,8 @@ static int insert_into_bitmap(struct btrfs_free_space_ctl *ctl,
 			goto out;
 		}
 	}
-again:
+
+no_cluster_bitmap:
 	bitmap_info = tree_search_offset(ctl, offset_to_bitmap(ctl, offset),
 					 1, 0);
 	if (!bitmap_info) {