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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 4C9B9C33C9E for ; Wed, 15 Jan 2020 01:07:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 16C3824681 for ; Wed, 15 Jan 2020 01:07:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728896AbgAOBHQ (ORCPT ); Tue, 14 Jan 2020 20:07:16 -0500 Received: from mga03.intel.com ([134.134.136.65]:5585 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728844AbgAOBHP (ORCPT ); Tue, 14 Jan 2020 20:07:15 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 14 Jan 2020 17:07:15 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,320,1574150400"; d="scan'208";a="256548046" Received: from unknown (HELO localhost) ([10.239.159.54]) by fmsmga002.fm.intel.com with ESMTP; 14 Jan 2020 17:07:12 -0800 Date: Wed, 15 Jan 2020 09:07:22 +0800 From: Wei Yang To: "Kirill A. Shutemov" Cc: Michal Hocko , Wei Yang , hannes@cmpxchg.org, vdavydov.dev@gmail.com, akpm@linux-foundation.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kirill.shutemov@linux.intel.com, yang.shi@linux.alibaba.com, alexander.duyck@gmail.com, rientjes@google.com Subject: Re: [Patch v2] mm: thp: grab the lock before manipulation defer list Message-ID: <20200115010722.GA4916@richard> Reply-To: Wei Yang References: <20200109143054.13203-1-richardw.yang@linux.intel.com> <20200111000352.efy6krudecpshezh@box> <20200114093122.GH19428@dhcp22.suse.cz> <20200114103112.o6ozdbkfnzdsc2ke@box> <20200114105921.eo2vdwikrvtt3gkb@box> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200114105921.eo2vdwikrvtt3gkb@box> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 14, 2020 at 01:59:21PM +0300, Kirill A. Shutemov wrote: >On Tue, Jan 14, 2020 at 01:31:12PM +0300, Kirill A. Shutemov wrote: >> On Tue, Jan 14, 2020 at 10:31:22AM +0100, Michal Hocko wrote: >> > On Sat 11-01-20 03:03:52, Kirill A. Shutemov wrote: >> > > On Thu, Jan 09, 2020 at 10:30:54PM +0800, Wei Yang wrote: >> > > > As all the other places, we grab the lock before manipulate the defer list. >> > > > Current implementation may face a race condition. >> > > > >> > > > For example, the potential race would be: >> > > > >> > > > CPU1 CPU2 >> > > > mem_cgroup_move_account split_huge_page_to_list >> > > > !list_empty >> > > > lock >> > > > !list_empty >> > > > list_del >> > > > unlock >> > > > lock >> > > > # !list_empty might not hold anymore >> > > > list_del_init >> > > > unlock >> > > >> > > I don't think this particular race is possible. Both parties take page >> > > lock before messing with deferred queue, but anytway: >> > > >> > > Acked-by: Kirill A. Shutemov >> > >> > I am confused, if the above race is not possible then what would be a >> > real race? We really do not want to have a patch with a misleading >> > changelog, do we? >> >> The alternative is to make sure that all page_deferred_list() called with >> page lock taken. >> >> I'll look into it. > >split_huge_page_to_list() has page lock taken. > >free_transhuge_page() is in the free path and doesn't susceptible to the >race. > >deferred_split_scan() is trickier. list_move() should be safe against >list_empty() as it will not produce false-positive list_empty(). >list_del_init() *should* (correct me if I'm wrong) be safe because the page >is freeing and memcg will not touch the page anymore. > >deferred_split_huge_page() is a problematic one. It called from >page_remove_rmap() path witch does require page lock. I don't see any >obvious way to exclude race with mem_cgroup_move_account() here. >Anybody else? If my understanding is correct, the reason is deferred_split_huge_page() doesn't has page lock taken, right? > >Wei, could you rewrite the commit message with deferred_split_huge_page() >as a race source instead of split_huge_page_to_list()? > >-- > Kirill A. Shutemov -- Wei Yang Help you, Help me