[CRIU] [PATCH 1/2] mnt: do_new_mount should restore sharing

[Tycho Andersen]

On Mon, Apr 20, 2015 at 08:10:31PM +0300, Andrey Wagin wrote:
> 2015-04-20 19:15 GMT+03:00 Tycho Andersen <tycho.andersen at canonical.com>:
> > On Mon, Apr 20, 2015 at 06:52:59PM +0300, Andrew Vagin wrote:
> >> On Fri, Apr 17, 2015 at 11:07:49AM -0600, Tycho Andersen wrote:
> >> > On Fri, Apr 17, 2015 at 06:58:34PM +0300, Andrew Vagin wrote:
> >> > > On Wed, Apr 15, 2015 at 01:17:40PM -0600, Tycho Andersen wrote:
> >> > > > The function masks off sharing in the initial setting, but doesn't correctly
> >> > > > reset the flags afterwards.
> >> > > >
> >> > > > CC: Oleg Nesterov <oleg at redhat.com>
> >> > > > Signed-off-by: Tycho Andersen <tycho.andersen at canonical.com>
> >> > > > ---
> >> > > >  mount.c | 4 +++-
> >> > > >  1 file changed, 3 insertions(+), 1 deletion(-)
> >> > > >
> >> > > > diff --git a/mount.c b/mount.c
> >> > > > index 1d8f486..17f97a2 100644
> >> > > > --- a/mount.c
> >> > > > +++ b/mount.c
> >> > > > @@ -1789,7 +1789,9 @@ static int do_new_mount(struct mount_info *mi)
> >> > > >                 return -1;
> >> > > >         }
> >> > > >
> >> > > > -       if (restore_shared_options(mi, 0, mi->shared_id, 0))
> >> > > > +       if (restore_shared_options(mi, !mi->shared_id && !mi->master_id,
> >> > >
> >> > > Could you explain this? If we talk about external mount, we need to give
> >> > > true here if host_mi->shared_id isn't equal to mi->shared_id.
> >> >
> >> > All external mounts are restored via do_bind_mount(), so the sharing
> >> > here is all internal.
> >>
> >> I mean auto external mounts.
> >>
> >> Lets imagine that we dump a mount point and find a pair on the host.
> >> On restore we bind-mount the host point into a restored point and a new
> >> mount point will inherit the host group. We know that these groups were
> >> different on dump, so we need to reset a group in the new mount point.
> >> For that we need to remount it as private and then as shared.
> >
> > Yes, that's what force_private_remount in do_bind_mount() is for.
> > Autodetected external mounts aren't restored via do_new_mount().
> 
> Sorry for my stupidity. I had to read code before commenting.

No problem,

> Acked-by: Andrew Vagin <avagin at odin.com>
> 
> >
> >> >
> >> > However, I think if this mi->shared_id differs from
> >> > mi->parent->shared_id we do need to remount private first, since the
> >> > internal sharing is different. I can resend with this change if it
> >> > makes sense.
> >>
> >> There is no correlation between mi->shared_id and mi->parent->shared_id.
> >
> > A mount inherits its parent's sharing when initially mounted, so if
> > the IDs differ, don't we need to re-mount private to get a new id?

I think this is still a problem with my patch?

Tycho