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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id EDCDFC433EF for ; Mon, 7 Mar 2022 05:21:53 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 82F0D8D0002; Mon, 7 Mar 2022 00:21:53 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 7DDAA8D0001; Mon, 7 Mar 2022 00:21:53 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6CCCA8D0002; Mon, 7 Mar 2022 00:21:53 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0045.hostedemail.com [216.40.44.45]) by kanga.kvack.org (Postfix) with ESMTP id 5C7248D0001 for ; Mon, 7 Mar 2022 00:21:53 -0500 (EST) Received: from smtpin30.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 0486F180AC330 for ; Mon, 7 Mar 2022 05:21:52 +0000 (UTC) X-FDA: 79216443306.30.BF2A711 Received: from mga02.intel.com (mga02.intel.com [134.134.136.20]) by imf28.hostedemail.com (Postfix) with ESMTP id 092ECC0003 for ; Mon, 7 Mar 2022 05:21:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1646630512; x=1678166512; h=from:to:cc:subject:references:date:in-reply-to: message-id:mime-version; bh=nENgkNrXPp9CG8WF2N13y7IyQBK8xft0YApUuFADoXQ=; b=BeENwCwmOsU5JG51NG7lulgJFfdaLuLPSCmfR7llpoSd5Lu9eyJYXztl N27WQffx1IsNJwExAn5rX4977NH7S0LnEtwpaTxPMflXhAp6HaAb4c9Hm xWJHMfzOrqmJ7a8akUow9CBX6qfhym6XpqmFrW+Tj+nDQVninZXuZequs ml8q97x+1PYxgP4tcuS0R+eo4FFkCheouaKdDXq/r79Jf/nucWB0Tchg5 qoxHBc0gtpvj0symJIkFKKZAOys7d347++LUhZUhVcw5T9AAC1ZQn3koq HjQgIdZu0zb/K5/zMRSs9GNoAskIT5+RyIiO73YMzWUUpf/jaUXLWfLaA Q==; X-IronPort-AV: E=McAfee;i="6200,9189,10278"; a="241733975" X-IronPort-AV: E=Sophos;i="5.90,160,1643702400"; d="scan'208";a="241733975" Received: from orsmga004.jf.intel.com ([10.7.209.38]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Mar 2022 21:21:50 -0800 X-IronPort-AV: E=Sophos;i="5.90,160,1643702400"; d="scan'208";a="643100514" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.239.13.94]) by orsmga004-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Mar 2022 21:21:45 -0800 From: "Huang, Ying" To: Miaohe Lin Cc: , , , , , , , , , , , , , , , , , Subject: Re: [PATCH 15/16] mm/migration: fix possible do_pages_stat_array racing with memory offline References: <20220304093409.25829-1-linmiaohe@huawei.com> <20220304093409.25829-16-linmiaohe@huawei.com> Date: Mon, 07 Mar 2022 13:21:43 +0800 In-Reply-To: <20220304093409.25829-16-linmiaohe@huawei.com> (Miaohe Lin's message of "Fri, 4 Mar 2022 17:34:08 +0800") Message-ID: <875yoq5od4.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 092ECC0003 X-Rspam-User: Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=BeENwCwm; spf=none (imf28.hostedemail.com: domain of ying.huang@intel.com has no SPF policy when checking 134.134.136.20) smtp.mailfrom=ying.huang@intel.com; dmarc=pass (policy=none) header.from=intel.com X-Stat-Signature: hfps665y1ghfd37t69jyijt1ic8799kh X-HE-Tag: 1646630511-406123 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: Miaohe Lin writes: > When follow_page peeks a page, the page could be reclaimed under heavy > memory pressure I don't think that memory pressure and reclaiming will be an issue. > and thus be offlined while it's still being used by the > do_pages_stat_array(). "offline" seems a possible problem. Best Regards, Huang, Ying > Use FOLL_GET to hold the page refcnt to fix this > potential issue. > > Signed-off-by: Miaohe Lin > --- > mm/migrate.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index 7b1c0b988234..98a968e6f465 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1788,13 +1788,18 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages, > goto set_status; > > /* FOLL_DUMP to ignore special (like zero) pages */ > - page = follow_page(vma, addr, FOLL_DUMP); > + page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP); > > err = PTR_ERR(page); > if (IS_ERR(page)) > goto set_status; > > - err = page ? page_to_nid(page) : -ENOENT; > + if (page) { > + err = page_to_nid(page); > + put_page(page); > + } else { > + err = -ENOENT; > + } > set_status: > *status = err;