[lxc-devel] [PATCH 1/1] pivot_root: switch to a new mechanism (v2)

[Eric W. Biederman]

Andy Lutomirski <luto at amacapital.net> writes:

> On Mon, Sep 29, 2014 at 4:22 PM, Eric W. Biederman
> <ebiederm at xmission.com> wrote:
>> Andy Lutomirski <luto at amacapital.net> writes:
>>
>>> To me, this smells like MNT_DETACH does something awful when there are
>>> mounts under the detached mount.
>>>
>>> For example:
>>>
>>> mount --rbind / /mnt
>>> umount -l /mnt
>>>
>>> does *not* end well on my system.  I find it hard to believe that this
>>> behavior is intentional.
>>
>> Hmm.  I think what is happening on your system is in some way related to
>> mount propgatation and systemd.   On my debian stable system system it
>> works without problems.
>
> Try the variant with mount --make-rshared / first.  I reproduced it in
> virtme, which doesn't use systemd -- it uses bash as its init daemon
> :)

Yes.  I so totally don't understand the motivation for the mount
propgation semantics but it appears that is what you triggered.

To test this I did:

mount --make-rshared /
mount --rbind / /mnt
mount --make-rprivate /mnt
umount -l /mnt

And the unmounts did not propgate to /.

Eric