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SubjectRe: [PATCH] btrfs: fix a resource leak in btrfs_init_sysfs()


On 2022/11/20 11:11, Qu Wenruo wrote:
>
>
> On 2022/11/19 14:53, Qu Wenruo wrote:
>>
>>
>> On 2022/11/19 14:43, Zhen Lei wrote:
>>> When btrfs_debug_feature_attr_group fails to be created,
>>> btrfs_feature_attr_group is not removed.
>>>
>>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>>
>> Reviewed-by: Qu Wenruo <wqu@suse.com>
>
> Wait for a minute, should we call sysfs_unmerge_group() first before
> calling sysfs_remove_group()?
>
> As the sysfs_remove_group() will only remove the
> btrfs_feature_attr_group, and kset_unregister() will only free
> btrfs_kset, without removing the added btrfs_static_feature_attr_group.
>
> I haven't yet find a function that will remove all children attrs in
> just one go, or did I miss something?

Oh, indeed I missed something.

The following call chain would properly handle every child of a kobj:

kset_unregister()
|- kobject_del()
|- __kobject_del()
|- sysfs_remove_dir()
|- kernfs_remove()
|- __kernfs_remove()
|- do { kernfs_leftmost_descendant(); } while (pos != kn)

The final do {} while () loop will unlink each child kernel_node and
free it.

This means, as long as we call kset_unregister(), we should be able to
free every child of it.


So with or without this patch, the error handling should be fine.

Although personally speaking, I'd prefer a more explicit cleanup (with
extra sysfs_unmerge_group() call) as going through the above call chain
is not that straightforward.

Thanks,
Qu

>
> Thanks,
> Qu
>>
>> Thanks,
>> Qu
>>> ---
>>>   fs/btrfs/sysfs.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
>>> index 699b54b3acaae0b..947125f2ceaaf96 100644
>>> --- a/fs/btrfs/sysfs.c
>>> +++ b/fs/btrfs/sysfs.c
>>> @@ -2322,7 +2322,7 @@ int __init btrfs_init_sysfs(void)
>>>   #ifdef CONFIG_BTRFS_DEBUG
>>>       ret = sysfs_create_group(&btrfs_kset->kobj,
>>> &btrfs_debug_feature_attr_group);
>>>       if (ret)
>>> -        goto out2;
>>> +        goto out_remove_group;
>>>   #endif
>>>       return 0;

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