linux-kernel - Re: [PATCH] oom killer: break from infinite loop

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Date:	Tue, 30 Mar 2010 23:07:08 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
cc:	anfei <anfei.zhou@...il.com>, Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	nishimura@....nes.nec.co.jp, Mel Gorman <mel@....ul.ie>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] oom killer: break from infinite loop

On Wed, 31 Mar 2010, KAMEZAWA Hiroyuki 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
> 

Then we should be able to do this since current is by definition 
unkillable since it was not found in select_bad_process(), right?
---
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -500,12 +500,9 @@ void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask)
 	read_lock(&tasklist_lock);
 retry:
 	p = select_bad_process(&points, limit, mem, CONSTRAINT_NONE, NULL);
-	if (PTR_ERR(p) == -1UL)
+	if (!p || PTR_ERR(p) == -1UL)
 		goto out;
 
-	if (!p)
-		p = current;
-
 	if (oom_kill_process(p, gfp_mask, 0, points, limit, mem,
 				"Memory cgroup out of memory"))
 		goto retry;
--
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