On Fri, 2022-07-15 at 06:47 -1000, Tejun Heo wrote:
> (resending, I messed up the message header, sorry)
>
> Hello,
>
> On Fri, Jul 15, 2022 at 01:59:38PM +0200, Michal Koutný wrote:
> > The css->rstat_css_node should not be modified if there are
> > possible RCU
> > readers elsewhere.
> > One way to fix this would be to insert synchronize_rcu() after
> > list_del_rcu() and before list_add_rcu().
> > (A further alternative (I've heard about) would be to utilize
> > 'nulls'
> > RCU lists [1] to make the move between lists detectable.)
> >
> > But as I'm looking at it from distance, it may be simpler and
> > sufficient
> > to just take cgroup_rstat_lock around the list migration (the
> > nesting
> > under cgroup_mutex that's held with rebind_subsystems() is fine).
>
> synchronize_rcu() prolly is the better fit here given how that
> list_node's
> usage, but yeah, great find.
>
> Thanks.
>
Hi Michal and Tejun,
Thanks for your suggestion.
Accroding your description, is the following patch corrent?
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1813,6 +1813,7 @@
if (ss->css_rstat_flush) {
list_del_rcu(&css->rstat_css_node);
+ synchronize_rcu();
list_add_rcu(&css->rstat_css_node,
&dcgrp->rstat_css_list);
}
If the patch is correct, we will add this patch to our stability test.
And we will continue to observe whether the problem is solved.
Thank you.
Best regards,
Jing-Ting Wu
