From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f72.google.com (mail-ed1-f72.google.com [209.85.208.72]) by kanga.kvack.org (Postfix) with ESMTP id 640ED6B000E for ; Mon, 6 Aug 2018 05:48:30 -0400 (EDT) Received: by mail-ed1-f72.google.com with SMTP id t17-v6so4014315edr.21 for ; Mon, 06 Aug 2018 02:48:30 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id b40-v6si899936edf.140.2018.08.06.02.48.29 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 06 Aug 2018 02:48:29 -0700 (PDT) Date: Mon, 6 Aug 2018 11:48:27 +0200 From: Michal Hocko Subject: Re: WARNING in try_charge Message-ID: <20180806094827.GH19540@dhcp22.suse.cz> References: <0000000000005e979605729c1564@google.com> <20180806091552.GE19540@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Dmitry Vyukov Cc: syzbot , cgroups@vger.kernel.org, Johannes Weiner , LKML , Linux-MM , syzkaller-bugs , Vladimir Davydov On Mon 06-08-18 11:30:37, Dmitry Vyukov wrote: > On Mon, Aug 6, 2018 at 11:15 AM, Michal Hocko wrote: [...] > > More interesting stuff is higher in the kernel log > > : [ 366.435015] oom-kill:constraint=CONSTRAINT_MEMCG,nodemask=(null),cpuset=/,mems_allowed=0,oom_memcg=/ile0,task_memcg=/ile0,task=syz-executor3,pid=23766,uid=0 > > : [ 366.449416] memory: usage 112kB, limit 0kB, failcnt 1605 > > > > Are you sure you want to have hard limit set to 0? > > syzkaller really does not mind to have it. So what do you use it for? What do you actually test by this setting? [...] > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index 4603ad75c9a9..852cd3dbdcd9 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -1388,6 +1388,8 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask, > > bool ret; > > > > mutex_lock(&oom_lock); > > + pr_info("task=%s pid=%d invoked memcg oom killer. oom_victim=%d\n", > > + current->comm, current->pid, tsk_is_oom_victim(current)); > > ret = out_of_memory(&oc); > > mutex_unlock(&oom_lock); > > return ret; > > > > Anyway your memcg setup is indeed misconfigured. Memcg with 0 hard limit > > and basically no memory charged by existing tasks is not going to fly > > and the warning is exactly to call that out. > > > Please-please-please do not mix kernel bugs and notices to user into > the same bucket: Well, WARN_ON used to be a standard way to make user aware of a misbehavior. In this case it warns about a pottential runaway when memcg is misconfigured. I do not insist on using WARN_ON here of course. If there is a general agreement that such a condition is better handled by pr_err then I am fine with it. Users tend to be more sensitive on WARN_ONs though. Btw. running with the above diff on top might help us to ideantify whether this is a pre-mature warning or a valid one. Still useful to find out. -- Michal Hocko SUSE Labs