From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753434AbcB2Sos (ORCPT ); Mon, 29 Feb 2016 13:44:48 -0500 Received: from mail-wm0-f54.google.com ([74.125.82.54]:35293 "EHLO mail-wm0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753147AbcB2Sor (ORCPT ); Mon, 29 Feb 2016 13:44:47 -0500 Date: Mon, 29 Feb 2016 19:44:44 +0100 From: Michal Hocko To: Vladimir Davydov Cc: Andrew Morton , Tetsuo Handa , David Rientjes , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] exit: clear TIF_MEMDIE after exit_task_work Message-ID: <20160229184444.GT16930@dhcp22.suse.cz> References: <1456765329-14890-1-git-send-email-vdavydov@virtuozzo.com> <20160229182131.GP16930@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160229182131.GP16930@dhcp22.suse.cz> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 29-02-16 19:21:31, Michal Hocko wrote: > On Mon 29-02-16 20:02:09, Vladimir Davydov wrote: > > An mm_struct may be pinned by a file. An example is vhost-net device > > created by a qemu/kvm (see vhost_net_ioctl -> vhost_net_set_owner -> > > vhost_dev_set_owner). If such process gets OOM-killed, the reference to > > its mm_struct will only be released from exit_task_work -> ____fput -> > > __fput -> vhost_net_release -> vhost_dev_cleanup, which is called after > > exit_mmap, where TIF_MEMDIE is cleared. As a result, we can start > > selecting the next victim before giving the last one a chance to free > > its memory. In practice, this leads to killing several VMs along with > > the fattest one. > > I am wondering why our PF_EXITING protection hasn't fired up. OK, I guess I can see it. exit_mm has done tsk->mm = NULL and so we are skipping over that task because oom_scan_process_thread hasn't checked PF_EXITING. I will try to think about this some more tomorrow with a fresh brain. -- Michal Hocko SUSE Labs