From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752096AbdG1NQS (ORCPT ); Fri, 28 Jul 2017 09:16:18 -0400 Received: from mail-by2nam01on0071.outbound.protection.outlook.com ([104.47.34.71]:26184 "EHLO NAM01-BY2-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751794AbdG1NQP (ORCPT ); Fri, 28 Jul 2017 09:16:15 -0400 Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=Manish.Jaggi@cavium.com; Subject: Re: Possible race condition in oom-killer To: Tetsuo Handa , Michal Hocko References: <20170728123235.GN2274@dhcp22.suse.cz> <46e1e3ee-af9a-4e67-8b4b-5cf21478ad21@I-love.SAKURA.ne.jp> Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org From: Manish Jaggi Message-ID: Date: Fri, 28 Jul 2017 18:45:53 +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: 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X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY1PR0701MB2076 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Tetsuo Handa, On 7/28/2017 6:29 PM, Tetsuo Handa wrote: > (Oops. Forgot to add CC.) > > On 2017/07/28 21:32, 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. > 4578 is consuming memory as mlocked pages. But the OOM reaper cannot reclaim > mlocked pages (i.e. can_madv_dontneed_vma() returns false due to VM_LOCKED), can it? > > oom02 0 TINFO : start OOM testing for mlocked pages. > oom02 0 TINFO : expected victim is 4578. > [ 365.267347] oom_reaper: reaped process 4578 (oom02), now anon-rss:131559616kB, file-rss:0kB, shmem-rss:0kB > > As a result, MMF_OOM_SKIP is set without reclaiming much memory. > Thus, it is natural that subsequent OOM victims are selected immediately because > almost all memory is still in use. Since 4578 is multi-threaded (isn't it?), > it will take time to call final __mmput() because mm->users are large. > Since there are many threads, it is possible that all OOM killable processes are > killed before final __mmput() of 4578 (which releases mlocked pages) is called. My setup has 95 or more cores, so the large number of cores could be the reason for the random failure? >> [...] >>>>> [ 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. > Because of mlocked pages by multi threaded process, it will take time to > reclaim mlocked pages. > >>> 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! >>