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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED,USER_AGENT_SANE_1 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 19CB3C32751 for ; Thu, 8 Aug 2019 02:10:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E2F56214C6 for ; Thu, 8 Aug 2019 02:10:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="ADL40Wec" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727889AbfHHCKw (ORCPT ); Wed, 7 Aug 2019 22:10:52 -0400 Received: from userp2130.oracle.com ([156.151.31.86]:53764 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727161AbfHHCKv (ORCPT ); Wed, 7 Aug 2019 22:10:51 -0400 Received: from pps.filterd (userp2130.oracle.com [127.0.0.1]) by userp2130.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x7828n9a075780; Thu, 8 Aug 2019 02:10:49 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=date : from : to : cc : subject : message-id : references : mime-version : content-type : in-reply-to; s=corp-2018-07-02; bh=TXriKJvJy2myVnw3c051jaeKryW3drWG0pSPjwioE5Q=; b=ADL40WecBnB1Z3f42497pGyz1FyclGQ12j8lMNgbk8lS2dQH08wmqTtk61/uTFlpsPhw zxrefhxHc33igYwECLs1R2GLPBjHP1B5tFfW2WTj/hrt6GUgi4z/JYrDBn7MrifRAIKT mnsrLpoihyFchsX613OBx61Y5hgEZxSKCIRpdTOh/U9zhRNJmq41K9QgLqXt+9Ac2oLm AjczwomaVHvfu9qBvXhwDvzDJQVUOLeQ/RPa5oCtTqZR55hnXUwmsUk1rdWDSb/MCSpg px81wxj13WmfCMA5n+Wwlu2bZLks8SAk5tzLwlCMAbRQHdlShrUj/KGgx5RQB60/nqL+ eA== Received: from aserp3020.oracle.com (aserp3020.oracle.com [141.146.126.70]) by userp2130.oracle.com with ESMTP id 2u51pu7q65-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 08 Aug 2019 02:10:49 +0000 Received: from pps.filterd (aserp3020.oracle.com [127.0.0.1]) by aserp3020.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x7828OEE109698; Thu, 8 Aug 2019 02:10:48 GMT Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by aserp3020.oracle.com with ESMTP id 2u7578h0y7-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 08 Aug 2019 02:10:48 +0000 Received: from abhmp0014.oracle.com (abhmp0014.oracle.com [141.146.116.20]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id x782Alj2012359; Thu, 8 Aug 2019 02:10:47 GMT Received: from localhost (/10.159.246.211) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Wed, 07 Aug 2019 19:10:47 -0700 Date: Wed, 7 Aug 2019 19:10:46 -0700 From: "Darrick J. Wong" To: Dave Chinner Cc: viro@zeniv.linux.org.uk, xfs , linux-fsdevel Subject: Re: [PATCH] vfs: fix page locking deadlocks when deduping files Message-ID: <20190808021046.GD7157@magnolia> References: <20190807145114.GP7138@magnolia> <20190807223850.GQ7777@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190807223850.GQ7777@dread.disaster.area> User-Agent: Mutt/1.9.4 (2018-02-28) X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9342 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=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908080020 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9342 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=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908080020 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Aug 08, 2019 at 08:38:50AM +1000, Dave Chinner wrote: > On Wed, Aug 07, 2019 at 07:51:14AM -0700, Darrick J. Wong wrote: > > From: Darrick J. Wong > > +/* > > + * Lock two pages, ensuring that we lock in offset order if the pages are from > > + * the same file. > > + */ > > +static void vfs_lock_two_pages(struct page *page1, struct page *page2) > > +{ > > + if (page1 == page2) { > > + lock_page(page1); > > + return; > > + } > > + > > + if (page1->mapping == page2->mapping && page1->index > page2->index) > > + swap(page1, page2); > > I would do this even if the pages are on different mappings. That > way we don't expose a landmine if some other code locks two pages > from the same mappings in a different order... Sure. > > + lock_page(page1); > > + lock_page(page2); > > +} > > + > > /* > > * Compare extents of two files to see if they are the same. > > * Caller must have locked both inodes to prevent write races. > > @@ -1867,10 +1881,12 @@ static int vfs_dedupe_file_range_compare(struct inode *src, loff_t srcoff, > > dest_page = vfs_dedupe_get_page(dest, destoff); > > if (IS_ERR(dest_page)) { > > error = PTR_ERR(dest_page); > > - unlock_page(src_page); > > put_page(src_page); > > goto out_error; > > } > > + > > + vfs_lock_two_pages(src_page, dest_page); > > + > > src_addr = kmap_atomic(src_page); > > dest_addr = kmap_atomic(dest_page); > > > > @@ -1882,7 +1898,8 @@ static int vfs_dedupe_file_range_compare(struct inode *src, loff_t srcoff, > > > > kunmap_atomic(dest_addr); > > kunmap_atomic(src_addr); > > - unlock_page(dest_page); > > + if (dest_page != src_page) > > + unlock_page(dest_page); > > unlock_page(src_page); > > Would it make sense for symmetry to wrap these in > vfs_unlock_two_pages()? Sure. --D > -Dave. > -- > Dave Chinner > david@fromorbit.com