Re: [-mm patch] Show memcg information during OOM

David Rientjes
2009-02-03T05:26:11Z

On Tue, 3 Feb 2009, Balbir Singh wrote:

> > > > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > > > > index d3b9bac..b8e53ae 100644
> > > > > --- a/mm/oom_kill.c
> > > > > +++ b/mm/oom_kill.c
> > > > > @@ -392,6 +392,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
> > > > > current->comm, gfp_mask, order, current->oomkilladj);
> > > > > task_lock(current);
> > > > > cpuset_print_task_mems_allowed(current);
> > > > > + mem_cgroup_print_mem_info(mem);
> > > >
> > > > I think this can be put outside the task lock. The lock is used to call task_cs() safely in
> > > > cpuset_print_task_mems_allowed().
> > > >
> > >
> > > Thanks, I'll work on that in the next version.
> > >
> >
> > I was also wondering about this and assumed that it was necessary to
> > prevent the cgroup from disappearing during the oom. If task_lock() isn't
> > held, is the memcg->css.cgroup->dentry->d_name.name dereference always
> > safe without rcu?
> >
>
> oom_kill_process is called with tasklist_lock held (read-mode). That
> should suffice, no? The memcg cannot go away since it has other groups
> or tasks associated with it.
>

I don't see how this prevents a task from being reattached to a different
cgroup and then a rmdir on memcg->css.cgroup would destroy the dentry
without cgroup_mutex or dereferencing via rcu.