[PATCH 4/5] cgroup: update iterators to use cgroup_next_sibling()

[Tejun Heo]

On Wed, May 22, 2013 at 05:09:02PM +0800, Li Zefan wrote:
> > @@ -3068,6 +3071,11 @@ EXPORT_SYMBOL_GPL(cgroup_next_descendant_pre);
> >   * Return the rightmost descendant of @pos.  If there's no descendant,
> >   * @pos is returned.  This can be used during pre-order traversal to skip
> >   * subtree of @pos.
> > + *
> > + * While this function requires RCU read locking, it doesn't require the
> > + * whole traversal to be contained in a single RCU critical section.  This
> > + * function will return the correct rightmost descendant as long as @pos is
> > + * accessible.
> >   */
> >  struct cgroup *cgroup_rightmost_descendant(struct cgroup *pos)
> >  {
> 
> Forgot to convert cgroup_rightmost_descendat() to use cgroup_next_sibling()?
> 
>         do {
>                 last = pos;
>                 /* ->prev isn't RCU safe, walk ->next till the end */
>                 pos = NULL;
>                 list_for_each_entry_rcu(tmp, &last->children, sibling)
>                         pos = tmp;
>         } while (pos);

It's always walking from the parent->children with RCU read locked, so
it doesn't need to be converted.  We can still convert it for
consistency and I had that in the patch originally but dropped it as
the conversion seemed a bit misleading as it covers a case which can
never happen.  Hmmm....

Thanks.

-- 
tejun