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@xxxxxxxxxx>
> >
> > Reviewed-by: Qu Wenruo <wqu@xxxxxxxx>
>
> 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;