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 AE986C33CAB for ; Mon, 13 Jan 2020 00:45:08 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 7C5A921556 for ; Mon, 13 Jan 2020 00:45:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7C5A921556 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 1753E8E0005; Sun, 12 Jan 2020 19:45:08 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 126928E0001; Sun, 12 Jan 2020 19:45:08 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 016508E0005; Sun, 12 Jan 2020 19:45:07 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0235.hostedemail.com [216.40.44.235]) by kanga.kvack.org (Postfix) with ESMTP id E05A28E0001 for ; Sun, 12 Jan 2020 19:45:07 -0500 (EST) Received: from smtpin30.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with SMTP id 9C791282A for ; Mon, 13 Jan 2020 00:45:07 +0000 (UTC) X-FDA: 76370766654.30.head90_2cb105017d258 X-HE-Tag: head90_2cb105017d258 X-Filterd-Recvd-Size: 3437 Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) by imf37.hostedemail.com (Postfix) with ESMTP for ; Mon, 13 Jan 2020 00:45:06 +0000 (UTC) X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 12 Jan 2020 16:45:05 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,427,1571727600"; d="scan'208";a="247559206" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by fmsmga004.fm.intel.com with ESMTP; 12 Jan 2020 16:45:03 -0800 Date: Mon, 13 Jan 2020 08:44:57 +0800 From: Wei Yang To: "Kirill A. Shutemov" Cc: Wei Yang , hannes@cmpxchg.org, mhocko@kernel.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: <20200113004457.GA27762@richard> Reply-To: Wei Yang References: <20200109143054.13203-1-richardw.yang@linux.intel.com> <20200111000352.efy6krudecpshezh@box> <20200112022858.GA17733@richard> <20200112225718.5vqzezfclacujyx3@box> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200112225718.5vqzezfclacujyx3@box> User-Agent: Mutt/1.9.4 (2018-02-28) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Jan 13, 2020 at 01:57:18AM +0300, Kirill A. Shutemov wrote: >On Sun, Jan 12, 2020 at 10:28:58AM +0800, Wei Yang wrote: >> On Sat, Jan 11, 2020 at 03:03:52AM +0300, 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: >> >> I am afraid not. Page lock is per page, while defer queue is per pgdate or >> memcg. >> >> It is possible two page in the same pgdate or memcg grab page lock >> respectively and then access the same defer queue concurrently. > >Look closer on the list_empty() argument. It's list_head local to the >page. Too different pages can be handled in parallel without any problem >in this particular scenario. As long as we as we modify it under the lock. > >Said that, page lock here was somewhat accidential and I still belive we >need to move the check under the lock anyway. > If my understanding is correct, you agree with my statement? >-- > Kirill A. Shutemov -- Wei Yang Help you, Help me