From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f177.google.com (mail-pd0-f177.google.com [209.85.192.177]) by kanga.kvack.org (Postfix) with ESMTP id AB55C6B0253 for ; Mon, 10 Aug 2015 04:51:56 -0400 (EDT) Received: by pdco4 with SMTP id o4so69268637pdc.3 for ; Mon, 10 Aug 2015 01:51:56 -0700 (PDT) Received: from tyo201.gate.nec.co.jp (TYO201.gate.nec.co.jp. [210.143.35.51]) by mx.google.com with ESMTPS id zp6si14717698pac.43.2015.08.10.01.51.55 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Mon, 10 Aug 2015 01:51:56 -0700 (PDT) From: Naoya Horiguchi Subject: Re: [PATCH 1/2] mm/hwpoison: fix fail to split THP w/ refcount held 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: Content-Language: ja-JP Content-Type: text/plain; charset="iso-2022-jp" Content-ID: <5E9D511B34238A458B93373B16FD5924@gisp.nec.co.jp> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: Wanpeng Li Cc: Andrew Morton , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" On Mon, Aug 10, 2015 at 04:29:18PM +0800, Wanpeng Li wrote: > Hi Naoya, >=20 > 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_INCREAS= ED > >>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? >=20 > 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org