Re: Possible bug: detached mounts difficult to cleanup

[Krister Johansen <kjlx-6woCzk5+qv5TrMCiz+cRkdBPR1lH4CV8@public.gmane.org>]

On Thu, Jan 12, 2017 at 09:26:20PM +1300, Eric W. Biederman wrote:
> At which point you have an island of mounts.
> 
> In that island each submount is on it's parent's mnt_pin list.
> When the last reference of a parent is dropped we call
>     umount_mnt on the children from mntput_no_expire
>     drop_mountpoint from mnt_pin_kill from cleanup_mnt indirectly from mntput_no_expire
> 
> So all we need is mntput_no_expire on a mount to be called for the
> entire island to be freed.
> 
> So the fundamental issue appears to be that nothing is dropping the last
> reference to some part of your island of mounts.

Ok, got it.  With the pointer from Andrei I was able to go back and
verify that the container's init process had live memory mappings from
files that were on the old root.  I apologize for the false alarm, and I
do appreciate you taking the time to explain the particulars.

-K