Btrfs: fix memory leak of block group cache

While processing delayed refs, we may update block group's statistics
and attach it to cur_trans->dirty_bgs, and later writing dirty block
groups will process the list, which happens during
btrfs_commit_transaction().

For whatever reason, the transaction is aborted and dirty_bgs
is not processed in cleanup_transaction(), we end up with memory leak
of these dirty block group cache.

Since btrfs_start_dirty_block_groups() doesn't make it go to the commit
critical section, this also adds the cleanup work inside it.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
index f19a982..1a3237e 100644
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -136,6 +136,8 @@
 			     struct btrfs_fs_info *fs_info);
 int btrfs_add_log_tree(struct btrfs_trans_handle *trans,
 		       struct btrfs_root *root);
+void btrfs_cleanup_dirty_bgs(struct btrfs_transaction *trans,
+			     struct btrfs_root *root);
 void btrfs_cleanup_one_transaction(struct btrfs_transaction *trans,
 				  struct btrfs_root *root);
 struct btrfs_root *btrfs_create_tree(struct btrfs_trans_handle *trans,