linux-kernel - Re: [PATCH] btrfs: fix a resource leak in btrfs_init

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Date:   Mon, 21 Nov 2022 11:49:56 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Qu Wenruo <quwenruo.btrfs@....com>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, <linux-btrfs@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] btrfs: fix a resource leak in btrfs_init_sysfs()



On 2022/11/20 11:29, Qu Wenruo wrote:
> 
> 
> 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@...wei.com>
>>>
>>> Reviewed-by: Qu Wenruo <wqu@...e.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.

OK, thanks.

> 
> 
> 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.

Yes, with sysfs_unmerge_group(), the code logic is clearer.

> 
> 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;
> .
> 

-- 
Regards,
  Zhen Lei