Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754359AbbHJJQc (ORCPT ); Mon, 10 Aug 2015 05:16:32 -0400 Received: from blu004-omc1s17.hotmail.com ([65.55.116.28]:59579 "EHLO BLU004-OMC1S17.hotmail.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753627AbbHJJQb (ORCPT ); Mon, 10 Aug 2015 05:16:31 -0400 X-TMN: [9aOava6C4F8Nb2fbRF2773rurIqMcud9] X-Originating-Email: [wanpeng.li@hotmail.com] Message-ID: Subject: Re: [PATCH 1/2] mm/hwpoison: fix fail to split THP w/ refcount held To: Naoya Horiguchi References: <20150810081019.GA21282@hori1.linux.bs1.fc.nec.co.jp> <20150810085047.GC21282@hori1.linux.bs1.fc.nec.co.jp> CC: Andrew Morton , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" From: Wanpeng Li Date: Mon, 10 Aug 2015 17:15:14 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:38.0) Gecko/20100101 Thunderbird/38.0.1 MIME-Version: 1.0 In-Reply-To: <20150810085047.GC21282@hori1.linux.bs1.fc.nec.co.jp> Content-Type: text/plain; charset="iso-2022-jp" Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 10 Aug 2015 09:16:29.0393 (UTC) FILETIME=[3DA54C10:01D0D34D] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1962 Lines: 56 On 8/10/15 4:50 PM, Naoya Horiguchi wrote: > On Mon, Aug 10, 2015 at 04:29:18PM +0800, Wanpeng Li wrote: >> Hi Naoya, >> >> On 8/10/15 4:10 PM, Naoya Horiguchi wrote: >>> On Mon, Aug 10, 2015 at 02:32:30PM +0800, Wanpeng Li wrote: >>>> THP pages will get a refcount in madvise_hwpoison() w/ MF_COUNT_INCREASED >>>> flag, however, the refcount is still held when fail to split THP pages. >>>> >>>> Fix it by reducing the refcount of THP pages when fail to split THP. >>>> >>>> Signed-off-by: Wanpeng Li >>> It seems that the same conditional put_page() would be added to >>> "soft offline: %#lx page already poisoned" branch too, right? >> PageHWPoison() is just called before the soft_offline_page() in >> madvise_hwpoion(). I think the PageHWPosion() >> check in soft_offline_page() makes more sense for the other >> soft_offline_page() callsites which don't have the >> refcount held. > What I am worried is a race like below: > > CPU0 CPU1 > > madvise_hwpoison > get_user_pages_fast > PageHWPoison check (false) > memory_failure > TestSetPageHWPoison > soft_offline_page > PageHWPoison check (true) > return -EBUSY (without put_page) Indeed, there is a race even through it is rared happen. > > It's rare and madvise_hwpoison() is testing feature, so this never causes > real problems in production systems, so it's not a big deal. > My suggestion is maybe just for code correctness thing ... Thanks for your proposal, I will add your suggestion in v2 and post out after we have a uniform solution for patch 2/2. :) Regards, Wanpeng Li > > Thanks, > Naoya Horiguchi -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/