btrfs: Fix lock release order

Locks should generally be released in the oppposite order they are
acquired. Generally lock acquisiton ordering is used to ensure
deadlocks don't happen. However, as becomes more complicated it's
best to also maintain proper unlock order so as to avoid possible dead
locks. This was found by code inspection and doesn't necessarily lead
to a deadlock scenario.
Signed-off-by: NNikolay Borisov <nborisov@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/extent-tree.c

@@ -2597,8 +2597,8 @@ static int cleanup_ref_head(struct btrfs_trans_handle *trans,
 	delayed_refs->num_heads--;
 	rb_erase(&head->href_node, &delayed_refs->href_root);
 	RB_CLEAR_NODE(&head->href_node);
-	spin_unlock(&delayed_refs->lock);
 	spin_unlock(&head->lock);
+	spin_unlock(&delayed_refs->lock);
 	atomic_dec(&delayed_refs->num_entries);
 
 	trace_run_delayed_ref_head(fs_info, head, 0);