On 09/16, Al Viro wrote:
> On Fri, Sep 15, 2017 at 04:29:11PM -0700, Jaegeuk Kim wrote:
>
> > The mntput() in delayed_fput() is the last function call. So before that
> > moment,
> > sys_umount() may see mnt_get_count() as 2, so it avoids EBUSY condition.
> > I'm not
> > sure why it check over 2 tho.
>
> Because it has just grabbed a reference itself, in addition to the one that
> keeps
> the damn thing alive (due to being mounted). So it bloody well should have
> triggered -EBUSY, if they refer to the same vfsmount.
I've tracked another view in terms of mnt_get_count() and sb->s_active based on
namespaces, and could get the below scenario for instance.
Term: namespace(mnt_get_count())
1. create_new_namespaces() creates ns1 and ns2,
/data(1) ns1(1) ns2(1)
| | |
---------------------
|
sb->s_active = 3
2. after binder_proc_clear_zombies() for ns2 and ns1 triggers
- delayed_fput()
- delayed_mntput_work(ns2)
/data(1) ns1(1)
| |
----------
|
sb->s_active = 2
3. umount() for /data is successed.
ns1(1)
|
sb->s_active = 1
4. device_shutdown() by init
5. - delayed_mntput_work(ns1)
- put_super(), since sb->s_active = 0
- -EIO
Please let me know, if I'm missing something.
Thanks,
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