From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3FF38C43610 for ; Wed, 10 Oct 2018 14:19:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D0E912087A for ; Wed, 10 Oct 2018 14:19:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D0E912087A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=i-love.sakura.ne.jp Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727128AbeJJVly (ORCPT ); Wed, 10 Oct 2018 17:41:54 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:16238 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726856AbeJJVly (ORCPT ); Wed, 10 Oct 2018 17:41:54 -0400 Received: from fsav107.sakura.ne.jp (fsav107.sakura.ne.jp [27.133.134.234]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id w9AEJTjF055365; Wed, 10 Oct 2018 23:19:29 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav107.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav107.sakura.ne.jp); Wed, 10 Oct 2018 23:19:29 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav107.sakura.ne.jp) Received: from [192.168.1.8] (softbank060157066051.bbtec.net [60.157.66.51]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id w9AEJNiC055313 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Wed, 10 Oct 2018 23:19:29 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: INFO: rcu detected stall in shmem_fault 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 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 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 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: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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