Re: [PATCH] oom killer: break from infinite loop

[KAMEZAWA Hiroyuki]

On Tue, 30 Mar 2010 13:29:29 -0700 (PDT)
David Rientjes <rientjes@xxxxxxxxxx> wrote:

> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > index 0cb1ca4..9e89a29 100644
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -510,8 +510,10 @@ retry:
> >  	if (PTR_ERR(p) == -1UL)
> >  		goto out;
> >  
> > -	if (!p)
> > -		p = current;
> > +	if (!p) {
> > +		read_unlock(&tasklist_lock);
> > +		panic("Out of memory and no killable processes...\n");
> > +	}
> >  
> >  	if (oom_kill_process(p, gfp_mask, 0, points, limit, mem,
> >  				"Memory cgroup out of memory"))
> > 
> 
> This actually does appear to be necessary but for a different reason: if 
> current is unkillable because it has OOM_DISABLE, for example, then 
> oom_kill_process() will repeatedly fail and mem_cgroup_out_of_memory() 
> will infinitely loop.
> 
> Kame-san?
> 

When a memcg goes into OOM and it only has unkillable processes (OOM_DISABLE),
we can do nothing. (we can't panic because container's death != system death.)

Because memcg itself has mutex+waitqueue for mutual execusion of OOM killer, 
I think infinite-loop will not be critical probelm for the whole system.

And, now, memcg has oom-kill-disable + oom-kill-notifier features.
So, If a memcg goes into OOM and there is no killable process, but oom-kill is
not disabled by memcg.....it means system admin's mis-configuraton.

He can stop inifite loop by hand, anyway.
# echo 1 > ..../group_A/memory.oom_control

Thanks,
-Kame


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