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 X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C4073C43387 for ; Fri, 4 Jan 2019 14:19:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9B7E521871 for ; Fri, 4 Jan 2019 14:19:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727330AbfADOTq (ORCPT ); Fri, 4 Jan 2019 09:19:46 -0500 Received: from mx1.redhat.com ([209.132.183.28]:58402 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726069AbfADOTq (ORCPT ); Fri, 4 Jan 2019 09:19:46 -0500 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D7CBDCD66C; Fri, 4 Jan 2019 14:19:45 +0000 (UTC) Received: from vitty.brq.redhat.com (unknown [10.43.2.155]) by smtp.corp.redhat.com (Postfix) with ESMTP id 38F645D9C5; Fri, 4 Jan 2019 14:19:44 +0000 (UTC) From: Vitaly Kuznetsov To: devel@linuxdriverproject.org Cc: Sasha Levin , "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , linux-kernel@vger.kernel.org, Dexuan Cui Subject: [PATCH] hv_balloon: avoid touching uninitialized struct page during tail onlining Date: Fri, 4 Jan 2019 15:19:42 +0100 Message-Id: <20190104141942.19126-1-vkuznets@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Fri, 04 Jan 2019 14:19:45 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hyper-V memory hotplug protocol has 2M granularity and in Linux x86 we use 128M. To deal with it we implement partial section onlining by registering custom page onlining callback (hv_online_page()). Later, when more memory arrives we try to online the 'tail' (see hv_bring_pgs_online()). It was found that in some cases this 'tail' onlining causes issues: BUG: Bad page state in process kworker/0:2 pfn:109e3a page:ffffe08344278e80 count:0 mapcount:1 mapping:0000000000000000 index:0x0 flags: 0xfffff80000000() raw: 000fffff80000000 dead000000000100 dead000000000200 0000000000000000 raw: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 page dumped because: nonzero mapcount ... Workqueue: events hot_add_req [hv_balloon] Call Trace: dump_stack+0x5c/0x80 bad_page.cold.112+0x7f/0xb2 free_pcppages_bulk+0x4b8/0x690 free_unref_page+0x54/0x70 hv_page_online_one+0x5c/0x80 [hv_balloon] hot_add_req.cold.24+0x182/0x835 [hv_balloon] ... Turns out that we now have deferred struct page initialization for memory hotplug so e.g. memory_block_action() in drivers/base/memory.c does pages_correctly_probed() check and in that check it avoids inspecting struct pages and checks sections instead. But in Hyper-V balloon driver we do PageReserved(pfn_to_page()) check and this is now wrong. Switch to checking online_section_nr() instead. Signed-off-by: Vitaly Kuznetsov --- drivers/hv/hv_balloon.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c index 5301fef16c31..7c6349a50ef1 100644 --- a/drivers/hv/hv_balloon.c +++ b/drivers/hv/hv_balloon.c @@ -888,12 +888,14 @@ static unsigned long handle_pg_range(unsigned long pg_start, pfn_cnt -= pgs_ol; /* * Check if the corresponding memory block is already - * online by checking its last previously backed page. - * In case it is we need to bring rest (which was not - * backed previously) online too. + * online. It is possible to observe struct pages still + * being uninitialized here so check section instead. + * In case the section is online we need to bring the + * rest of pfns (which were not backed previously) + * online too. */ if (start_pfn > has->start_pfn && - !PageReserved(pfn_to_page(start_pfn - 1))) + online_section_nr(pfn_to_section_nr(start_pfn))) hv_bring_pgs_online(has, start_pfn, pgs_ol); } -- 2.20.1