From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752093AbdG1NvG (ORCPT ); Fri, 28 Jul 2017 09:51:06 -0400 Received: from mail-bn3nam01on0042.outbound.protection.outlook.com ([104.47.33.42]:15446 "EHLO NAM01-BN3-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751673AbdG1NvE (ORCPT ); Fri, 28 Jul 2017 09:51:04 -0400 Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=Manish.Jaggi@cavium.com; Subject: Re: Possible race condition in oom-killer To: Michal Hocko References: <20170728123235.GN2274@dhcp22.suse.cz> Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org From: Manish Jaggi Message-ID: <88cbd07e-6e5e-924f-cdd3-82e65722ed30@caviumnetworks.com> Date: Fri, 28 Jul 2017 19:20:42 +0530 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <20170728123235.GN2274@dhcp22.suse.cz> 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X-MS-Exchange-Transport-CrossTenantHeadersStamped: BLUPR0701MB2065 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Michal, On 7/28/2017 6:02 PM, Michal Hocko wrote: > [CC linux-mm] > > On Fri 28-07-17 17:22:25, Manish Jaggi wrote: >> was: Re: [PATCH] mm, oom: allow oom reaper to race with exit_mmap >> >> Hi Michal, >> On 7/27/2017 2:54 PM, Michal Hocko wrote: >>> On Thu 27-07-17 13:59:09, Manish Jaggi wrote: >>> [...] >>>> With 4.11.6 I was getting random kernel panics (Out of memory - No process left to kill), >>>> when running LTP oom01 /oom02 ltp tests on our arm64 hardware with ~256G memory and high core count. >>>> The issue experienced was as follows >>>> that either test (oom01/oom02) selected a pid as victim and waited for the pid to be killed. >>>> that pid was marked as killed but somewhere there is a race and the process didnt get killed. >>>> and the oom01/oom02 test started killing further processes, till it panics. >>>> IIUC this issue is quite similar to your patch description. But applying your patch I still see the issue. >>>> If it is not related to this patch, can you please suggest by looking at the log, what could be preventing >>>> the killing of victim. >>>> >>>> Log (https://pastebin.com/hg5iXRj2) >>>> >>>> As a subtest of oom02 starts, it prints out the victim - In this case 4578 >>>> >>>> oom02 0 TINFO : start OOM testing for mlocked pages. >>>> oom02 0 TINFO : expected victim is 4578. >>>> >>>> When oom02 thread invokes oom-killer, it did select 4578 for killing... >>> I will definitely have a look. Can you report it in a separate email >>> thread please? Are you able to reproduce with the current Linus or >>> linux-next trees? >> Yes this issue is visible with linux-next. > Could you provide the full kernel log from this run please? I do not > expect there to be much difference but just to be sure that the code I > am looking at matches logs. The log is here: https://pastebin.com/Pmn5ZwEM mlocked memory keeps on increasing till panic. > [...] >>>> [ 365.283361] oom02:4586 invoked oom-killer: gfp_mask=0x16040c0(GFP_KERNEL|__GFP_COMP|__GFP_NOTRACK), nodemask=1, order=0, oom_score_adj=0 >>> Yes because >>> [ 365.283499] Node 1 Normal free:19500kB min:33804kB low:165916kB high:298028kB active_anon:13312kB inactive_anon:172kB active_file:0kB inactive_file:1044kB unevictable:131560064kB writepending:0kB present:134213632kB managed:132113248kB mlocked:131560064kB slab_reclaimable:5748kB slab_unreclaimable:17808kB kernel_stack:2720kB pagetables:254636kB bounce:0kB free_pcp:10476kB local_pcp:144kB free_cma:0kB >>> >>> Although we have killed and reaped oom02 process Node1 is still below >>> min watermark and that is why we have hit the oom killer again. It >>> is not immediatelly clear to me why, that would require a deeper >>> inspection. >> I have a doubt here >> my understanding of oom test: oom() function basically forks itself and >> starts n threads each thread has a loop which allocates and touches memory >> thus will trigger oom-killer and will kill the process. the parent process >> is on a wait() and will print pass/fail. >> >> So IIUC when 4578 is reaped all the child threads should be terminated, >> which happens in pass case (line 152) >> But even after being killed and reaped, the oom killer is invoked again >> which doesn't seem right. > As I've said the OOM killer hits because the memory from Node 1 didn't > get freed for some reasov or got immediatally populated. > >> Could it be that the process is just marked hidden from oom including its >> threads, thus oom-killer continues. > The whole process should be killed and the OOM reaper should only mark > the victim oom invisible _after_ the address space has been reaped (and > memory freed). You said the patch from > http://lkml.kernel.org/r/20170724072332.31903-1-mhocko@kernel.org didn't > help so it shouldn't be a race with the last __mmput. > > Thanks!