> > static struct vfsmount *propagation_next(struct vfsmount *p,
> >                                      struct vfsmount *base)
> > {
> >     /* first iterate over the slaves */
> >     if (!list_empty(&p->mnt_slave_list))
> >             return first_slave(p);
> 
> I think this code should be
>               if (!list_empty(&p->mnt_slave))
>                       return next_slave(p);
> 
> Right? I think I get the idea. 

This is a depth-first search, so first_slave() is right.

Here's a less buggy (and even more simplified) version of the
function.  Note: it must be called with 'origin' either on a slave
list or at the root pnode.  That's because the function checks if the
all vfsmounts in a pnode have been traversed by looking at the
emptiness of mnt_slave.  So if origin was in a slave pnode, but is not
the actual slave link, the algorithm will go off the starting pnode
and up to it's master.

So here's a preparation function that finds the right place to start
the propagation.

static struct vfsmount *propagation_first(struct vfsmount *p)
{
        struct vfsmount *q = p;

        while (list_empty(&q->mnt_slave)) {
                q = next_shared(q);
                if (q == p)
                        break;
        }
        return q;
}

static struct vfsmount *propagation_next(struct vfsmount *p,
                                         struct vfsmount *origin)
{
        /* are there any slaves of this mount? */
        if (!list_empty(&p->mnt_slave_list))
                return first_slave(p);

        while (1) {
                /* if p->mnt_share is empty, this is a no-op */
                p = next_shared(p);

                /* finished traversing? */
                if (p == origin)
                        break;

                /* more vfsmounts belong to the pnode? */
                if (list_empty(&p->mnt_slave))
                        return p;
                
                /* more slaves? */
                if (p->mnt_slave.next != &p->mnt_master->mnt_slave_list)
                        return next_slave(p);

                /* back at master */
                p = p->mnt_master;
        }

        return NULL;
}

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