Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934873AbcLPMNJ (ORCPT ); Fri, 16 Dec 2016 07:13:09 -0500 Received: from mail-wj0-f195.google.com ([209.85.210.195]:35044 "EHLO mail-wj0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934688AbcLPMNB (ORCPT ); Fri, 16 Dec 2016 07:13:01 -0500 Date: Fri, 16 Dec 2016 13:12:58 +0100 From: Michal Hocko To: "Kirill A. Shutemov" Cc: Vegard Nossum , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Rik van Riel , Matthew Wilcox , Peter Zijlstra , Andrew Morton , Al Viro , Ingo Molnar , Linus Torvalds Subject: Re: crash during oom reaper Message-ID: <20161216121258.GI13940@dhcp22.suse.cz> References: <20161216082202.21044-1-vegard.nossum@oracle.com> <20161216082202.21044-4-vegard.nossum@oracle.com> <20161216090157.GA13940@dhcp22.suse.cz> <20161216101113.GE13940@dhcp22.suse.cz> <20161216104438.GD27758@node> <20161216114243.GG13940@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161216114243.GG13940@dhcp22.suse.cz> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1868 Lines: 46 On Fri 16-12-16 12:42:43, Michal Hocko wrote: > On Fri 16-12-16 13:44:38, Kirill A. Shutemov wrote: > > On Fri, Dec 16, 2016 at 11:11:13AM +0100, Michal Hocko wrote: > > > On Fri 16-12-16 10:43:52, Vegard Nossum wrote: > > > [...] > > > > I don't think it's a bug in the OOM reaper itself, but either of the > > > > following two patches will fix the problem (without my understand how or > > > > why): > > > > > > > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > > > > index ec9f11d4f094..37b14b2e2af4 100644 > > > > --- a/mm/oom_kill.c > > > > +++ b/mm/oom_kill.c > > > > @@ -485,7 +485,7 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, > > > > struct mm_struct *mm) > > > > */ > > > > mutex_lock(&oom_lock); > > > > > > > > - if (!down_read_trylock(&mm->mmap_sem)) { > > > > + if (!down_write_trylock(&mm->mmap_sem)) { > > > > > > __oom_reap_task_mm is basically the same thing as MADV_DONTNEED and that > > > doesn't require the exlusive mmap_sem. So this looks correct to me. > > > > BTW, shouldn't we filter out all VM_SPECIAL VMAs there? Or VM_PFNMAP at > > least. > > > > MADV_DONTNEED doesn't touch VM_PFNMAP, but I don't see anything matching > > on __oom_reap_task_mm() side. > > I guess you are right and we should match the MADV_DONTNEED behavior > here. Care to send a patch? > > > Other difference is that you use unmap_page_range() witch doesn't touch > > mmu_notifiers. MADV_DONTNEED goes via zap_page_range(), which invalidates > > the range. Not sure if it can make any difference here. > > Which mmu notifier would care about this? I am not really familiar with > those users so I might miss something easily. Just forgot to add. Unlike the MADV_DONTNEED, there is nobody who should observe the address space of the oom killed (and reaped) task so why should notifiers matter in the first place? -- Michal Hocko SUSE Labs