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

Josef Bacik
2020-03-13T17:39:46Z

On 3/13/20 1:38 PM, David Sterba wrote:
> 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.
>

Because I looked at it and thought it was needed and was confused and had to go
look when you replied when you said it wasn't. So it's needed for clarity sake ;).

Josef