linux-kernel - Re: [BUGFIX][PATCH -mmotm] memcg: avoid oom-killing innocent task in case of use

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20091125032954.GC3365@balbir.in.ibm.com>
Date:	Wed, 25 Nov 2009 08:59:55 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, stable <stable@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [BUGFIX][PATCH -mmotm] memcg: avoid oom-killing innocent task
	in case of use_hierarchy

* nishimura@....nes.nec.co.jp <nishimura@....nes.nec.co.jp> [2009-11-25 08:49:10]:

> On Tue, 24 Nov 2009 22:34:02 +0530, Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> > * Daisuke Nishimura <d-nishimura@....biglobe.ne.jp> [2009-11-24 23:00:29]:
> > 
> > > On Tue, 24 Nov 2009 19:01:54 +0530
> > > Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> > > 
> > > > On Tue, Nov 24, 2009 at 11:27 AM, Daisuke Nishimura
> > > > <nishimura@....nes.nec.co.jp> wrote:
> > > > > task_in_mem_cgroup(), which is called by select_bad_process() to check whether
> > > > > a task can be a candidate for being oom-killed from memcg's limit, checks
> > > > > "curr->use_hierarchy"("curr" is the mem_cgroup the task belongs to).
> > > > >
> > > > > But this check return true(it's false positive) when:
> > > > >
> > > > >        <some path>/00          use_hierarchy == 0      <- hitting limit
> > > > >          <some path>/00/aa     use_hierarchy == 1      <- "curr"
> > > > >
> > > > > This leads to killing an innocent task in 00/aa. This patch is a fix for this
> > > > > bug. And this patch also fixes the arg for mem_cgroup_print_oom_info(). We
> > > > > should print information of mem_cgroup which the task being killed, not current,
> > > > > belongs to.
> > > > >
> > > > 
> > > > Quick Question: What happens if <some path>/00 has no tasks in it
> > > > after your patches?
> > > > 
> > > Nothing would happen because <some path>/00 never hit its limit.
> > 
> > Why not? I am talking of a scenario where <some path>/00 is set to a
> > limit (similar to your example) and hits its limit, but the groups
> > under it have no limits, but tasks. Shouldn't we be scanning
> > <some path>/00/aa as well?
> > 
> > > 
> > > The bug that this patch fixes is:
> > > 
> > > - create a dir <some path>/00 and set some limits.
> > > - create a sub dir <some path>/00/aa w/o any limits, and enable hierarchy.
> > > - run some programs in both in 00 and 00/aa. programs in 00 should be
> > >   big enough to cause oom by its limit.
> > > - when oom happens by 00's limit, tasks in 00/aa can also be killed.
> > >
> > 
> > To be honest, the last part is fair, specifically if 00/aa has a task
> > that is really the heaviest task as per the oom logic. no? Are you
> > suggesting that only tasks in <some path>/00 should be selected by the
> > oom logic? 
> > 
> All of your comments would be rational if hierarchy is enabled in 00(it's
> also enabled in 00/aa automatically in this case).
> I'm saying about the case where it's disabled in 00 but enabled in 00/aa.
> 

OK, I misunderstood the example then, so even though hierarchy is
disabled, we kill a task in 00/aa when 00 hits the limit. Thanks for
clarifying.

> In this scenario, charges by tasks in 00/aa is(and should not be) charged to 00.
> And oom caused by 00's limit should not affect the task in 00/aa.
> 
> 
> Regards,
> Daisuke Nishimura.
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@...ck.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a>
> 

-- 
	Balbir
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/