Re: [PATCH 4/8] btrfs: free the reloc_control in a consistent way

[David Sterba <dsterba@suse.cz>]

On Fri, Mar 13, 2020 at 06:18:51PM +0100, David Sterba wrote:
> On Fri, Mar 13, 2020 at 11:44:44AM -0400, Josef Bacik wrote:
> > If we have an error while processing the reloc roots we could leak roots
> > that were added to rc->reloc_roots before we hit the error.  We could
> > have also not removed the reloct tree mapping from our rb_tree, so clean
> > up any remaining nodes in the reloc root rb_tree.
> > 
> > Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> > ---
> >  fs/btrfs/relocation.c | 18 ++++++++++++++++--
> >  1 file changed, 16 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
> > index c496f8ed8c7e..721d049ff2b5 100644
> > --- a/fs/btrfs/relocation.c
> > +++ b/fs/btrfs/relocation.c
> > @@ -4387,6 +4387,20 @@ static struct reloc_control *alloc_reloc_control(struct btrfs_fs_info *fs_info)
> >  	return rc;
> >  }
> >  
> > +static void free_reloc_control(struct reloc_control *rc)
> > +{
> > +	struct mapping_node *node, *tmp;
> > +
> > +	free_reloc_roots(&rc->reloc_roots);
> > +	rbtree_postorder_for_each_entry_safe(node, tmp,
> > +					     &rc->reloc_root_tree.rb_root,
> > +					     rb_node) {
> > +		rb_erase(&node->rb_node, &rc->reloc_root_tree.rb_root);
> 
> The rb_erase is not needed here, the postorder traversal just goes over
> all nodes and allows to free the containing structures together with the
> rb_node. Dangling pointers are not an issue.

I had not seen your reply when I replied to the v2 patch but if you
think the rb_erase is needed, I don't see why.