potential null derefs in fs/btrfs/relocation.c

Hi hi,

Still going through some more smatch stuff and there are two potential null dereferences in fs/btrfs/relocation.c

This was introduced by 3fd0a5585e: "Btrfs: Metadata ENOSPC handling for balance"

fs/btrfs/relocation.c +791 build_backref_tree(142)
warn: variable dereferenced before check 'root'
787 root = find_tree_root(rc, eb, ref0);
788 if (!root->ref_cows)

                             ^^^^^^^^^^^^^^
	dereference here.

   789                          cur->cowonly = 1;
   790                  if (key.objectid == key.offset) {
   791                          if (root && !should_ignore_root(root))
                                   ^^^^^^^^

check here.

   792                                  cur->root = root;
   793                          else
   794                                  list_add(&cur->list, &useless);
   795                          break;
   796                  }

fs/btrfs/relocation.c +1241 __update_reloc_root(15)
error: potential null derefence 'node'.

  1229          struct mapping_node *node = NULL;
                                    ^^^^^^^^^^^^^

1230 struct reloc_control *rc = root->fs_info->reloc_ctl;
1231
1232 spin_lock(&rc->reloc_root_tree.lock);
1233 rb_node = tree_search(&rc->reloc_root_tree.rb_root,
1234 root->commit_root->start);
1235 if (rb_node) {
1236 node = rb_entry(rb_node, struct mapping_node, rb_node);
1237 rb_erase(&node->rb_node, &rc->reloc_root_tree.rb_root);
1238 }
1239 spin_unlock(&rc->reloc_root_tree.lock);
1240
1241 BUG_ON((struct btrfs_root *)node->data != root);
^^^^^^^^^^
if tree_search() returns NULL it will oops here.

regards,
dan carpenter