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

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Date:   Sun, 13 Mar 2022 01:01:33 +0900
From:   Ryusuke Konishi <konishi.ryusuke@...il.com>
To:     Pavel Skripkin <paskripkin@...il.com>,
        Dongliang Mu <mudongliangabcd@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-nilfs <linux-nilfs@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Nanyong Sun <sunnanyong@...wei.com>,
        慕冬亮 <dzm91@...t.edu.cn>
Subject: Re: Fw:Re: [PATCH] fs: nilfs2: fix memory leak in nilfs sysfs create
 device group

Hi Pavel and Dongliang,

On Sun, Mar 13, 2022 at 12:16 AM Pavel Skripkin <paskripkin@...il.com> wrote:
>
> Hi Ryusuke,
>
> On 3/12/22 18:11, Ryusuke Konishi wrote:
> >> In case of nilfs_attach_log_writer() error code jumps to
> >> failed_checkpoint label and calls destroy_nilfs() which should call
> >> nilfs_sysfs_delete_device_group().
> >
> > nilfs_sysfs_delete_device_group() is called in destroy_nilfs()
> > if nilfs->ns_flags has THE_NILFS_INIT flag -- nilfs_init() inline
> > function tests this flag.
> >
> > The flag is set after init_nilfs() succeeded at the beginning of
> > nilfs_fill_super() because the set_nilfs_init() inline in init_nilfs() sets it.
> >
> > So,  nilfs_sysfs_delete_group() seems to be called in case of
> > the above failure.   Am I missing something?
> >
>
> Yeah, that's what I mean :) I can't see how reported issue is possible
> with current code.
>
>
> Sorry for not being clear

Understood, thanks for the reply.

If so,  the case where nilfs_sysfs_create_device_group() itself failed,
is suspicious as mentioned in the previous mail.   A possible scenario
I guess is :

- nilfs_sysfs_create_device_group() on the first mount try fails and leaks
  due to lack of kobject_del() in the error path.
- Then, nilfs_sysfs_create_device_group() on the next mount try hits
  the leak detector at kobject_init_and_add().

So, if the leak bug is reproducible, I'd like to ask Dongliang to
test the effect of the first patch.

Regards,
Ryusuke Konishi

>
>
>
> With regards,
> Pavel Skripkin