Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754292AbbHJIv7 (ORCPT ); Mon, 10 Aug 2015 04:51:59 -0400 Received: from TYO201.gate.nec.co.jp ([210.143.35.51]:63031 "EHLO tyo201.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753426AbbHJIv5 convert rfc822-to-8bit (ORCPT ); Mon, 10 Aug 2015 04:51:57 -0400 From: Naoya Horiguchi To: Wanpeng Li CC: Andrew Morton , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 1/2] mm/hwpoison: fix fail to split THP w/ refcount held Thread-Topic: [PATCH 1/2] mm/hwpoison: fix fail to split THP w/ refcount held Thread-Index: AQHQ00mmrpmY78MOJEO3FyG/xBR8qQ== Date: Mon, 10 Aug 2015 08:50:47 +0000 Message-ID: <20150810085047.GC21282@hori1.linux.bs1.fc.nec.co.jp> References: <20150810081019.GA21282@hori1.linux.bs1.fc.nec.co.jp> In-Reply-To: Accept-Language: ja-JP, en-US Content-Language: ja-JP X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.128.101.31] Content-Type: text/plain; charset="iso-2022-jp" Content-ID: <5E9D511B34238A458B93373B16FD5924@gisp.nec.co.jp> Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1664 Lines: 43 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) 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, 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/