Re: Fw:Re: [PATCH] fs: nilfs2: fix memory leak in nilfs sysfs create device group

[Dongliang Mu]

>
> From： Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
> Date： 01/21/2022 01:54
> To： Dongliang Mu <dzm91@xxxxxxxxxxx>
> Cc： Pavel Skripkin <paskripkin@xxxxxxxxx> 、 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> 、 linux-nilfs <linux-nilfs@xxxxxxxxxxxxxxx> 、 LKML <linux-kernel@xxxxxxxxxxxxxxx> 、 Nanyong Sun <sunnanyong@xxxxxxxxxx>
> Subject： Re: [PATCH] fs: nilfs2: fix memory leak in nilfs_sysfs_create_device_group
> (added Nanyong Sun to CC)
> Hi Dongliang,
>
> On Thu, Jan 20, 2022 at 11:07 PM Pavel Skripkin <paskripkin@xxxxxxxxx> 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 ?

Hi Pavel,

This is an incorrect fixes tag. I need to dig more about `git log -p
fs/nilfs2/sysfs.c`.

I wonder if there are any automatic or semi-automatic ways to capture
this fixes tag. Or how do you guys identify the fixes tag?

>
> 5f5dec07aca7 ("nilfs2: fix memory leak in nilfs_sysfs_create_device_group")
>
> Signed-off-by: Dongliang Mu <dzm91@xxxxxxxxxxx>
> ---
> 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

I know where my problem is. From the disconnect function, I think the
kobject_del and kobject_put are both necessary without checking the
documentation of kobjects.

Then I think the current error handling may miss kobject_del, and this
patch is generated.

As a result, I think we can ignore this patch. Sorry for my false alarm.

>
>
> 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