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

    On Tue, Mar 15, 2022 at 2:50 PM Dongliang Mu <mudongliangabcd@gmail.com> wrote:
    >
    > On Tue, Mar 15, 2022 at 12:46 PM Ryusuke Konishi
    > <konishi.ryusuke@gmail.com> wrote:
    > >
    > > On Tue, Mar 15, 2022 at 10:59 AM Dongliang Mu <mudongliangabcd@gmail.com> wrote:
    > > >
    > > > On Sun, Mar 13, 2022 at 9:35 PM Dongliang Mu <mudongliangabcd@gmail.com> wrote:
    > > > >
    > > > > On Sun, Mar 13, 2022 at 12:01 AM Ryusuke Konishi
    > > > > <konishi.ryusuke@gmail.com> wrote:
    > > > > >
    > > > > > Hi Pavel and Dongliang,
    > > > > >
    > > > > > On Sun, Mar 13, 2022 at 12:16 AM Pavel Skripkin <paskripkin@gmail.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.
    > > > >
    > > > > If my local syzkaller instance gets a reproducer, I will try to do this.
    > > > >
    > > > > >
    > > > > > Regards,
    > > > > > Ryusuke Konishi
    > > >
    > > > Hi Ryusuke,
    > > >
    > > > The crash still occurred in my newly set up syzkaller instance. It
    > > > appears after two days' fuzzing.
    > > >
    > > > I remember you suggested me to add kobject_del just for testing,
    > > > right? And let's see if this crash still occurs any more.
    > >
    > > You need a few days to reproduce it ?
    > > If so, I think this confirmation method is uncertain.
    > > In that case, I will try inserting an artificial error by changing
    > > nilfs_sysfs_create_device_group() a bit to confirm if the same crash occurs.

    I tried to change the code of nilfs_sysfs_create_device_group() so that
    an error occurs once every two times.
    As a result, the leak bug was not reproduced.

    In addition, by kobject debug messages, I saw that the device name
    ("loop2" in your case) was properly freed through kobject_put() even in
    the erroneous case.

    So, my previous guess was wrong.
    Looks like there is another cause for the leak of the device name.
    It may not be a nilfs2 issue, I don't know.

    > I am reproducing another bug [1] recently. If you can spare some time
    > figuring out the underlying issue, that's really great. Or we can wait
    > some time for the bug to disclose more, after all, it is only a rare
    > memory leak.
    >
    > [1] https://syzkaller.appspot.com/bug?extid=045796dbe294d53147e6

    According to the log, it looks like "erofs_put_super() ->
    erofs_unregister_sysfs()" hits:

    kobject: '(null)' (ffff88807b550190): is not initialized, yet
    kobject_put() is being called.

    This warning is output in kobject_put() if kobj argument is not in
    'state_initialized':

    void kobject_put(struct kobject *kobj)
    {
    if (kobj) {
    if (!kobj->state_initialized)
    WARN(1, KERN_WARNING
    "kobject: '%s' (%p): is not
    initialized, yet kobject_put() is being called.\n",
    kobject_name(kobj), kobj);
    kref_put(&kobj->kref, kobject_release);
    }
    }

    How about chasing this abnormal condition ?
    Anyway, please ask erofs maintainers and linux-erofs mailing list for this.

    Regards,
    Ryusuke Konishi

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