From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f51.google.com (mail-oi0-f51.google.com [209.85.218.51]) by kanga.kvack.org (Postfix) with ESMTP id CD0126B0253 for ; Mon, 10 Aug 2015 05:16:31 -0400 (EDT) Received: by oihn130 with SMTP id n130so84877234oih.2 for ; Mon, 10 Aug 2015 02:16:31 -0700 (PDT) Received: from BLU004-OMC1S17.hotmail.com (blu004-omc1s17.hotmail.com. [65.55.116.28]) by mx.google.com with ESMTPS id ru3si13957012obc.104.2015.08.10.02.16.31 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 10 Aug 2015 02:16:31 -0700 (PDT) Message-ID: Subject: Re: [PATCH 1/2] mm/hwpoison: fix fail to split THP w/ refcount held References: <20150810081019.GA21282@hori1.linux.bs1.fc.nec.co.jp> <20150810085047.GC21282@hori1.linux.bs1.fc.nec.co.jp> From: Wanpeng Li Date: Mon, 10 Aug 2015 17:15:14 +0800 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 Sender: owner-linux-mm@kvack.org List-ID: To: Naoya Horiguchi Cc: Andrew Morton , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" 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, 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