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=-5.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 A3649C4363D for ; Thu, 24 Sep 2020 02:06:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 53EE82223E for ; Thu, 24 Sep 2020 02:06:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="CfRSMVkR" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726565AbgIXCGc (ORCPT ); Wed, 23 Sep 2020 22:06:32 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:23098 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726500AbgIXCGb (ORCPT ); Wed, 23 Sep 2020 22:06:31 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1600913189; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=x8ZHcIulSGOzBD8uxM6rgIoMK8J76Sbkt6GTxH94yuI=; b=CfRSMVkRA1d3uhsTz8cFF9z3ftAHQBBa4YzXwo6EsNb/sijJj0hhBn5w66SEHMz2/0UlRC UNyUlujR6C1udl5Ds8OcQpYUGelqsKFLUTM4wjWPswEPVtb0Cw8CcTVl3I6ENioLlCE/fM aMZSmdJEGKS8qF2iS3Q/aoPJM/AgT20= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-321-pYJrqiROO7OZqblLvyigNw-1; Wed, 23 Sep 2020 22:06:26 -0400 X-MC-Unique: pYJrqiROO7OZqblLvyigNw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 32F51188C122; Thu, 24 Sep 2020 02:06:24 +0000 (UTC) Received: from ovpn-66-35.rdu2.redhat.com (unknown [10.10.67.35]) by smtp.corp.redhat.com (Postfix) with ESMTP id AD1B860C17; Thu, 24 Sep 2020 02:06:19 +0000 (UTC) Message-ID: <76fef5dfd8efdb4130e41d1811b2a78ce39c8b0d.camel@redhat.com> Subject: Re: BUG: Bad page state in process dirtyc0w_child From: Qian Cai To: Gerald Schaefer , Linus Torvalds , Peter Xu Cc: Heiko Carstens , Alexander Gordeev , Vasily Gorbik , Christian Borntraeger , linux-s390@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Alex Shi Date: Wed, 23 Sep 2020 22:06:19 -0400 In-Reply-To: <20200923153938.5be5dd2c@thinkpad> References: <20200916142806.GD7076@osiris> <20200922190350.7a0e0ca5@thinkpad> <20200923153938.5be5dd2c@thinkpad> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2020-09-23 at 15:39 +0200, Gerald Schaefer wrote: > OK, I can now reproduce this, and unfortunately also with the gup_fast > fix, so it is something different. Bisecting is a bit hard, as it will > not always show immediately, sometimes takes up to an hour. > > Still, I think I found the culprit, merge commit b25d1dc9474e "Merge > branch 'simplify-do_wp_page'". Without those 4 patches, it works fine, > running over night. > > Not sure why this only shows on s390, should not be architecture-specific, > but we do often see subtle races earlier than others due to hypervisor > impact. Apparently, someone can reproduce something similar on x86 as well: https://lore.kernel.org/linux-mm/c41149a8-211e-390b-af1d-d5eee690fecb@linux.alibaba.com/ Probably, Alex could revert the bad commits and confirm it there. > > The first commit 09854ba94c6a ("mm: do_wp_page() simplification") already > introduces this error. The dirtyc0w_child test seems to play with cow > and racing madvise(MADV_DONTNEED), but I have not yet fully understood > it and also not the changes from commit 09854ba94c6a. As Linus already > mentioned in the merge commit message, this is some bad timing for such > a change, so I don't want to delay this further with trying to understand > it better before reporting. Maybe Peter or Linus can spot some obvious > issue. > > One thing that seems strange to me is that the page flags from the > bad page state output are (uptodate|swapbacked), see below, or > (referenced|uptodate|dirty|swapbacked) in the original report. But IIUC, > that should not qualify for the "PAGE_FLAGS_CHECK_AT_FREE flag(s) set" > reason. So it seems that the flags have changed between check_free_page() > and __dump_page(), which would be very odd. Or maybe some issue with > compound pages, because __dump_page() looks at head->flags. > > [ 1863.237707] BUG: Bad page state in process dirtyc0w_child pfn:58527d > [ 1863.237721] page:000000008866956b refcount:0 mapcount:0 > mapping:0000000000000000 index:0x0 pfn:0x58527d > [ 1863.237727] flags: 0x3ffff00000080004(uptodate|swapbacked) > [ 1863.237734] raw: 3ffff00000080004 0000000000000100 0000000000000122 > 0000000000000000 > [ 1863.237738] raw: 0000000000000000 0000000000000000 ffffffff00000000 > 0000000000000000 > [ 1863.237742] page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set > [ 1863.237745] Modules linked in: > [ 1863.237752] CPU: 16 PID: 9074 Comm: dirtyc0w_child Tainted: > G B 5.9.0-rc6-00020-geff48ddeab78-dirty #104 > [ 1863.237756] Hardware name: IBM 3906 M03 703 (LPAR) > [ 1863.237759] Call Trace: > [ 1863.237768] [<0000000000115f28>] show_stack+0x100/0x158 > [ 1863.237775] [<000000000096b41a>] dump_stack+0xa2/0xd8 > [ 1863.237781] [<00000000003d497c>] bad_page+0xdc/0x140 > [ 1863.237785] [<00000000003d5b62>] free_pcp_prepare+0x31a/0x360 > [ 1863.237789] [<00000000003d906a>] free_unref_page+0x32/0xb8 > [ 1863.237794] [<00000000003b05f4>] zap_p4d_range+0x64c/0xcf8 > [ 1863.237797] [<00000000003b0e7a>] unmap_page_range+0x9a/0x110 > [ 1863.237801] [<00000000003b0f84>] unmap_single_vma+0x94/0x100 > [ 1863.237805] [<00000000003b14c2>] zap_page_range+0x14a/0x1f0 > [ 1863.237809] [<00000000003e3a24>] do_madvise+0x75c/0x918 > [ 1863.237812] [<00000000003e3c06>] __s390x_sys_madvise+0x26/0x38 > [ 1863.237817] [<0000000000d280d4>] system_call+0xe0/0x2c0 > [ 1863.237820] INFO: lockdep is turned off. >