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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, 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 06FA9C282CE for ; Tue, 9 Apr 2019 03:30:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C945F21473 for ; Tue, 9 Apr 2019 03:30:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="zPUCIEg5" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727148AbfDIDaa (ORCPT ); Mon, 8 Apr 2019 23:30:30 -0400 Received: from aserp2130.oracle.com ([141.146.126.79]:39174 "EHLO aserp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726492AbfDIDaa (ORCPT ); Mon, 8 Apr 2019 23:30:30 -0400 Received: from pps.filterd (aserp2130.oracle.com [127.0.0.1]) by aserp2130.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x393T152151814; Tue, 9 Apr 2019 03:30:19 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : to : references : from : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2018-07-02; bh=yNAnix0vPb3Rl0k78u1G6bUYV+iub+YsxxG7ebwDs7U=; b=zPUCIEg5CUbDsP0wiNhIk8OvKl7JmuJp/okBnahAcSyFxQGyUIBX0mUXXvSDwxGePx48 NrjyTdGtU6SokLBju1C5MHRO0FJXgs6UmehpqLkJwBelmrbkxGxMum3xPyNtznCJKNyK tsuyXYXsx+cmTxCu9OF5v546DaJIpch/WUPBPAU0Awd6uy7o5zpfnAy6J79W1BDCI29d wZxF0RYoFjH9WuwuJIQcM/3JVB+lqv5g3l++SgMFyFu8b5baxaJCrool/xQ0LfBpjJc5 bG42V9v+I+cQdSbMNEUon2THP8ovxp9E6fz/8kazU/0MNxC81zFK+2hjaBsRWs5b615w Fw== Received: from aserp3030.oracle.com (aserp3030.oracle.com [141.146.126.71]) by aserp2130.oracle.com with ESMTP id 2rphmeacg6-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 09 Apr 2019 03:30:19 +0000 Received: from pps.filterd (aserp3030.oracle.com [127.0.0.1]) by aserp3030.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x393TlYX158719; Tue, 9 Apr 2019 03:30:18 GMT Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by aserp3030.oracle.com with ESMTP id 2rpj5aava2-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 09 Apr 2019 03:30:18 +0000 Received: from abhmp0003.oracle.com (abhmp0003.oracle.com [141.146.116.9]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x393UFQU025909; Tue, 9 Apr 2019 03:30:16 GMT Received: from [192.168.1.222] (/50.38.38.67) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 08 Apr 2019 20:30:15 -0700 Subject: Re: [PATCH v2 0/2] A couple hugetlbfs fixes To: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Joonsoo Kim , Michal Hocko , Naoya Horiguchi , "Kirill A . Shutemov" , Andrew Morton References: <20190328234704.27083-1-mike.kravetz@oracle.com> <20190408194815.77d4mftojhkrgbhv@linux-r8p5> From: Mike Kravetz Message-ID: Date: Mon, 8 Apr 2019 20:30:14 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190408194815.77d4mftojhkrgbhv@linux-r8p5> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9221 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=923 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1904090022 X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9221 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=933 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1904090023 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/8/19 12:48 PM, Davidlohr Bueso wrote: > On Thu, 28 Mar 2019, Mike Kravetz wrote: > >> - A BUG can be triggered (not easily) due to temporarily mapping a >> page before doing a COW. > > But you actually _have_ seen it? Do you have the traces? I ask > not because of the patches perse, but because it would be nice > to have a real snipplet in the Changelog for patch 2. Yes, I actually saw this problem. It happened while I was debugging and testing some patches for hugetlb migration. The BUG I hit was in unaccount_page_cache_page(): VM_BUG_ON_PAGE(page_mapped(page), page). Stack trace was something like: unaccount_page_cache_page __delete_from_page_cache delete_from_page_cache remove_huge_page remove_inode_hugepages hugetlbfs_punch_hole hugetlbfs_fallocate When I hit that, it took me a while to figure out how it could happen. i.e. How could a page be mapped at that point in remove_inode_hugepages? It checks page_mapped and we are holding the fault mutex. With some additional debug code (strategic udelays) I could hit the issue on a somewhat regular basis and verified another thread was in the hugetlb_no_page/hugetlb_cow path for the same page at the same time. Unfortunately, I did not save the traces. I am trying to recreate now. However, my test system was recently updated and it might take a little time to recreate. -- Mike Kravetz