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

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

[Zhen Lei]

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>
---
 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;
-- 
2.25.1

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

[Qu Wenruo]

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>

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;

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

[Qu Wenruo]

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?

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;

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

[Qu Wenruo]

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;

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

[Leizhen (ThunderTown)]

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@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.

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