btrfs: fix free space calculation in dump_space_info()

In btrfs, btrfs_space_info's bytes_may_use is treated as fs used
space, as what we do in reserve_metadata_bytes() or
btrfs_alloc_data_chunk_ondemand(), so in dump_space_info(), when
calculating free space, we should also subtract btrfs_space_info's
bytes_may_use.

Signed-off-by: Wang Xiaoguang <wangxg.fnst@cn.fujitsu.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent-tree.c

@@ -7906,8 +7906,8 @@ static void dump_space_info(struct btrfs_space_info *info, u64 bytes,
 	printk(KERN_INFO "BTRFS: space_info %llu has %llu free, is %sfull\n",
 	       info->flags,
 	       info->total_bytes - info->bytes_used - info->bytes_pinned -
-	       info->bytes_reserved - info->bytes_readonly,
-	       (info->full) ? "" : "not ");
+	       info->bytes_reserved - info->bytes_readonly -
+	       info->bytes_may_use, (info->full) ? "" : "not ");
 	printk(KERN_INFO "BTRFS: space_info total=%llu, used=%llu, pinned=%llu, "
 	       "reserved=%llu, may_use=%llu, readonly=%llu\n",
 	       info->total_bytes, info->bytes_used, info->bytes_pinned,