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 167F5C32771 for ; Tue, 7 Jan 2020 01:22:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DAF2E20715 for ; Tue, 7 Jan 2020 01:22:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727384AbgAGBWj (ORCPT ); Mon, 6 Jan 2020 20:22:39 -0500 Received: from mga17.intel.com ([192.55.52.151]:6547 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727295AbgAGBWi (ORCPT ); Mon, 6 Jan 2020 20:22:38 -0500 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by fmsmga107.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 06 Jan 2020 17:22:38 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,404,1571727600"; d="scan'208";a="420887474" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by fmsmga005.fm.intel.com with ESMTP; 06 Jan 2020 17:22:36 -0800 Date: Tue, 7 Jan 2020 09:22:41 +0800 From: Wei Yang To: Michal Hocko Cc: Wei Yang , hannes@cmpxchg.org, vdavydov.dev@gmail.com, akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, yang.shi@linux.alibaba.com Subject: Re: [RFC PATCH] mm: thp: grab the lock before manipulation defer list Message-ID: <20200107012241.GA15341@richard> Reply-To: Wei Yang References: <20200103143407.1089-1-richardw.yang@linux.intel.com> <20200106102345.GE12699@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200106102345.GE12699@dhcp22.suse.cz> 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 Mon, Jan 06, 2020 at 11:23:45AM +0100, Michal Hocko wrote: >On Fri 03-01-20 22:34:07, Wei Yang wrote: >> As all the other places, we grab the lock before manipulate the defer list. >> Current implementation may face a race condition. > >Please always make sure to describe the effect of the change. Why a racy >list_empty check matters? > Hmm... access the list without proper lock leads to many bad behaviors. For example, if we grab the lock after checking list_empty, the page may already be removed from list in split_huge_page_list. And then list_del_init would trigger bug. -- Wei Yang Help you, Help me