Re: PROBLEM: BUG when using memory.kmem.limit_in_bytes

[Vladimir Davydov <vdavydov-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org>]

On Fri, Jan 22, 2016 at 10:51:04AM -0500, Tejun Heo wrote:
> On Fri, Jan 22, 2016 at 09:48:54AM -0500, Johannes Weiner wrote:
> > On Fri, Jan 22, 2016 at 04:50:42PM +0300, Vladimir Davydov wrote:
> > > From first glance, it looks like the bug was triggered, because
> > > mem_cgroup_css_offline was run for a child cgroup earlier than for its
> > > parent. This couldn't happen for sure before the cgroup was switched to
> > > percpu_ref, because cgroup_destroy_wq has always had max_active == 1.
> > > Now, however, it looks like this is perfectly possible for
> > > css_killed_ref_fn is called from an rcu callback - see kill_css ->
> > > percpu_ref_kill_and_confirm. This breaks kmemcg assumptions.
> > > 
> > > I'll take a look what can be done about that.
> > 
> > It's an acknowledged problem in the cgroup core then, and not an issue
> > with kmemcg. Tejun sent a fix to correct the offlining order here:
> > 
> > https://www.mail-archive.com/linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org/msg1056544.html
> 
> Patche descriptions updated and applied to cgroup/for-4.5-fixes.
> 
>  http://lkml.kernel.org/g/20160122154503.GD32380-piEFEHQLUPpN0TnZuCh8vA@public.gmane.org
>  http://lkml.kernel.org/g/20160122154552.GE32380-piEFEHQLUPpN0TnZuCh8vA@public.gmane.org

I couldn't reproduce the issue with the two patches applied. Looks like
they fix it.

Thanks,
Vladimir