From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ot1-f72.google.com (mail-ot1-f72.google.com [209.85.210.72]) by kanga.kvack.org (Postfix) with ESMTP id 740666B000A for ; Wed, 10 Oct 2018 10:19:52 -0400 (EDT) Received: by mail-ot1-f72.google.com with SMTP id j47so3748913ota.16 for ; Wed, 10 Oct 2018 07:19:52 -0700 (PDT) Received: from www262.sakura.ne.jp (www262.sakura.ne.jp. [202.181.97.72]) by mx.google.com with ESMTPS id 74-v6si11694508oie.75.2018.10.10.07.19.50 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 10 Oct 2018 07:19:51 -0700 (PDT) Subject: Re: INFO: rcu detected stall in shmem_fault References: <000000000000dc48d40577d4a587@google.com> <201810100012.w9A0Cjtn047782@www262.sakura.ne.jp> <20181010085945.GC5873@dhcp22.suse.cz> <20181010113500.GH5873@dhcp22.suse.cz> From: Tetsuo Handa Message-ID: <127c73bd-2c7b-6ef0-3c6d-5e01d43bdf5b@i-love.sakura.ne.jp> Date: Wed, 10 Oct 2018 23:19:21 +0900 MIME-Version: 1.0 In-Reply-To: <20181010113500.GH5873@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: syzbot , hannes@cmpxchg.org, akpm@linux-foundation.org, guro@fb.com, kirill.shutemov@linux.intel.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, rientjes@google.com, syzkaller-bugs@googlegroups.com, yang.s@alibaba-inc.com, Sergey Senozhatsky , Sergey Senozhatsky , Petr Mladek On 2018/10/10 20:35, Michal Hocko wrote: >>>> What should we do if memcg-OOM found no killable task because the allocating task >>>> was oom_score_adj == -1000 ? Flooding printk() until RCU stall watchdog fires >>>> (which seems to be caused by commit 3100dab2aa09dc6e ("mm: memcontrol: print proper >>>> OOM header when no eligible victim left") because syzbot was terminating the test >>>> upon WARN(1) removed by that commit) is not a good behavior. >>> >>> We definitely want to inform about ineligible oom victim. We might >>> consider some rate limiting for the memcg state but that is a valuable >>> information to see under normal situation (when you do not have floods >>> of these situations). >>> >> >> But if the caller cannot be noticed by SIGKILL from the OOM killer, >> allowing the caller to trigger the OOM killer again and again (until >> global OOM killer triggers) is bad. > > There is simply no other option. Well, except for failing the charge > which has been considered and refused because it could trigger > unexpected error paths and that breaking the isolation on rare cases > when of the misconfiguration is acceptable. We can reconsider that > but you should bring really good arguments on the table. I was very > successful doing that. > By the way, how do we avoid this flooding? Something like this? include/linux/sched.h | 1 + mm/oom_kill.c | 11 +++++++++++ 2 files changed, 12 insertions(+) diff --git a/include/linux/sched.h b/include/linux/sched.h index 977cb57..58eff50 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -723,6 +723,7 @@ struct task_struct { #endif #ifdef CONFIG_MEMCG unsigned in_user_fault:1; + unsigned memcg_oom_no_eligible_warned:1; #ifdef CONFIG_MEMCG_KMEM unsigned memcg_kmem_skip_account:1; #endif diff --git a/mm/oom_kill.c b/mm/oom_kill.c index f10aa53..ff0fa65 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -1106,6 +1106,13 @@ bool out_of_memory(struct oom_control *oc) select_bad_process(oc); /* Found nothing?!?! */ if (!oc->chosen) { +#ifdef CONFIG_MEMCG + if (is_memcg_oom(oc)) { + if (current->memcg_oom_no_eligible_warned) + return false; + current->memcg_oom_no_eligible_warned = 1; + } +#endif dump_header(oc, NULL); pr_warn("Out of memory and no killable processes...\n"); /* @@ -1115,6 +1122,10 @@ bool out_of_memory(struct oom_control *oc) */ if (!is_sysrq_oom(oc) && !is_memcg_oom(oc)) panic("System is deadlocked on memory\n"); +#ifdef CONFIG_MEMCG + } else if (is_memcg_oom(oc)) { + current->memcg_oom_no_eligible_warned = 0; +#endif } if (oc->chosen && oc->chosen != (void *)-1UL) oom_kill_process(oc, !is_memcg_oom(oc) ? "Out of memory" : -- 1.8.3.1