[PATCH] fs: nilfs2: fix memory leak in nilfs_sysfs_create_device_group

[PATCH] fs: nilfs2: fix memory leak in nilfs_sysfs_create_device_group

[Dongliang Mu]

The preivous commit 8fd0c1b0647a ("nilfs2: fix memory leak in
nilfs_sysfs_delete_device_group") only handles the memory leak in the
nilfs_sysfs_delete_device_group. However, the similar memory leak still
occurs in the nilfs_sysfs_create_device_group.

Fix it by adding kobject_del when
kobject_init_and_add succeeds, but one of the following calls fails.

Fixes: 8fd0c1b0647a ("nilfs2: fix memory leak in nilfs_sysfs_delete_device_group")
Signed-off-by: Dongliang Mu <dzm91@hust.edu.cn>
---
 fs/nilfs2/sysfs.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/nilfs2/sysfs.c b/fs/nilfs2/sysfs.c
index 379d22e28ed6..0b2db2b499d5 100644
--- a/fs/nilfs2/sysfs.c
+++ b/fs/nilfs2/sysfs.c
@@ -995,7 +995,7 @@ int nilfs_sysfs_create_device_group(struct super_block *sb)
 
 	err = nilfs_sysfs_create_mounted_snapshots_group(nilfs);
 	if (err)
-		goto cleanup_dev_kobject;
+		goto delete_dev_kobject;
 
 	err = nilfs_sysfs_create_checkpoints_group(nilfs);
 	if (err)
@@ -1027,6 +1027,9 @@ int nilfs_sysfs_create_device_group(struct super_block *sb)
 delete_mounted_snapshots_group:
 	nilfs_sysfs_delete_mounted_snapshots_group(nilfs);
 
+delete_dev_kobject:
+	kobject_del(&nilfs->ns_dev_kobj);
+
 cleanup_dev_kobject:
 	kobject_put(&nilfs->ns_dev_kobj);
 	kfree(nilfs->ns_dev_subgroups);
-- 
2.25.1

Re: [PATCH] fs: nilfs2: fix memory leak in nilfs_sysfs_create_device_group

[Pavel Skripkin]

Hi Dongliang,

On 1/20/22 16:44, Dongliang Mu wrote:
> The preivous commit 8fd0c1b0647a ("nilfs2: fix memory leak in
> nilfs_sysfs_delete_device_group") only handles the memory leak in the
> nilfs_sysfs_delete_device_group. However, the similar memory leak still
> occurs in the nilfs_sysfs_create_device_group.
> 
> Fix it by adding kobject_del when
> kobject_init_and_add succeeds, but one of the following calls fails.
> 
> Fixes: 8fd0c1b0647a ("nilfs2: fix memory leak in nilfs_sysfs_delete_device_group")

Why Fixes tag points to my commit? This issue was introduced before my patch

> Signed-off-by: Dongliang Mu <dzm91@hust.edu.cn>
> ---
>   fs/nilfs2/sysfs.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/nilfs2/sysfs.c b/fs/nilfs2/sysfs.c
> index 379d22e28ed6..0b2db2b499d5 100644
> --- a/fs/nilfs2/sysfs.c
> +++ b/fs/nilfs2/sysfs.c
> @@ -995,7 +995,7 @@ int nilfs_sysfs_create_device_group(struct super_block *sb)
>   
>   	err = nilfs_sysfs_create_mounted_snapshots_group(nilfs);
>   	if (err)
> -		goto cleanup_dev_kobject;
> +		goto delete_dev_kobject;
>   
>   	err = nilfs_sysfs_create_checkpoints_group(nilfs);
>   	if (err)
> @@ -1027,6 +1027,9 @@ int nilfs_sysfs_create_device_group(struct super_block *sb)
>   delete_mounted_snapshots_group:
>   	nilfs_sysfs_delete_mounted_snapshots_group(nilfs);
>   
> +delete_dev_kobject:
> +	kobject_del(&nilfs->ns_dev_kobj);
> +
>   cleanup_dev_kobject:
>   	kobject_put(&nilfs->ns_dev_kobj);
>   	kfree(nilfs->ns_dev_subgroups);
With regards,
Pavel Skripkin

Re: [PATCH] fs: nilfs2: fix memory leak in nilfs_sysfs_create_device_group

[Ryusuke Konishi]

(added Nanyong Sun to CC)
Hi Dongliang,

On Thu, Jan 20, 2022 at 11:07 PM Pavel Skripkin <paskripkin@gmail.com> wrote:
>
> Hi Dongliang,
>
> On 1/20/22 16:44, Dongliang Mu wrote:
> > The preivous commit 8fd0c1b0647a ("nilfs2: fix memory leak in
> > nilfs_sysfs_delete_device_group") only handles the memory leak in the
> > nilfs_sysfs_delete_device_group. However, the similar memory leak still
> > occurs in the nilfs_sysfs_create_device_group.
> >
> > Fix it by adding kobject_del when
> > kobject_init_and_add succeeds, but one of the following calls fails.
> >
> > Fixes: 8fd0c1b0647a ("nilfs2: fix memory leak in nilfs_sysfs_delete_device_group")
>
> Why Fixes tag points to my commit? This issue was introduced before my patch
>

As Pavel pointed out, this patch is independent of his patch.
The following one ?

 5f5dec07aca7 ("nilfs2: fix memory leak in nilfs_sysfs_create_device_group")

> > Signed-off-by: Dongliang Mu <dzm91@hust.edu.cn>
> > ---
> >   fs/nilfs2/sysfs.c | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)

Can you describe what memory leak issue does this patch actually fix ?

It looks like kobject_put() can call __kobject_del() unless circular
references exist.

  kobject_put() -> kref_put() -> kobject_release() ->
kobject_cleanup() -> __kobject_del()

As explained in Documentation/core-api/kobject.rst,

  kobject_del() can be used to drop the reference to the parent object, if
  circular references are constructed.

But, at least, the parent object is NULL in this case.
I really want to understand what the real problem is.

Thanks,
Ryusuke Konishi

> >
> > diff --git a/fs/nilfs2/sysfs.c b/fs/nilfs2/sysfs.c
> > index 379d22e28ed6..0b2db2b499d5 100644
> > --- a/fs/nilfs2/sysfs.c
> > +++ b/fs/nilfs2/sysfs.c
> > @@ -995,7 +995,7 @@ int nilfs_sysfs_create_device_group(struct super_block *sb)
> >
> >       err = nilfs_sysfs_create_mounted_snapshots_group(nilfs);
> >       if (err)
> > -             goto cleanup_dev_kobject;
> > +             goto delete_dev_kobject;
> >
> >       err = nilfs_sysfs_create_checkpoints_group(nilfs);
> >       if (err)
> > @@ -1027,6 +1027,9 @@ int nilfs_sysfs_create_device_group(struct super_block *sb)
> >   delete_mounted_snapshots_group:
> >       nilfs_sysfs_delete_mounted_snapshots_group(nilfs);
> >
> > +delete_dev_kobject:
> > +     kobject_del(&nilfs->ns_dev_kobj);
> > +
> >   cleanup_dev_kobject:
> >       kobject_put(&nilfs->ns_dev_kobj);
> >       kfree(nilfs->ns_dev_subgroups);
> With regards,
> Pavel Skripkin