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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 85956C32751 for ; Wed, 7 Aug 2019 22:40:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5B1A621743 for ; Wed, 7 Aug 2019 22:40:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389109AbfHGWkB (ORCPT ); Wed, 7 Aug 2019 18:40:01 -0400 Received: from mail105.syd.optusnet.com.au ([211.29.132.249]:52686 "EHLO mail105.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388133AbfHGWkB (ORCPT ); Wed, 7 Aug 2019 18:40:01 -0400 Received: from dread.disaster.area (pa49-181-167-148.pa.nsw.optusnet.com.au [49.181.167.148]) by mail105.syd.optusnet.com.au (Postfix) with ESMTPS id 0B4A0361C58; Thu, 8 Aug 2019 08:39:57 +1000 (AEST) Received: from dave by dread.disaster.area with local (Exim 4.92) (envelope-from ) id 1hvUa2-00067h-MZ; Thu, 08 Aug 2019 08:38:50 +1000 Date: Thu, 8 Aug 2019 08:38:50 +1000 From: Dave Chinner To: "Darrick J. Wong" Cc: viro@zeniv.linux.org.uk, xfs , linux-fsdevel Subject: Re: [PATCH] vfs: fix page locking deadlocks when deduping files Message-ID: <20190807223850.GQ7777@dread.disaster.area> References: <20190807145114.GP7138@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190807145114.GP7138@magnolia> User-Agent: Mutt/1.10.1 (2018-07-13) X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.2 cv=P6RKvmIu c=1 sm=1 tr=0 a=gu9DDhuZhshYSb5Zs/lkOA==:117 a=gu9DDhuZhshYSb5Zs/lkOA==:17 a=jpOVt7BSZ2e4Z31A5e1TngXxSK0=:19 a=kj9zAlcOel0A:10 a=FmdZ9Uzk2mMA:10 a=yPCof4ZbAAAA:8 a=7-415B0cAAAA:8 a=UD9wB-r_hoJu2ZtOc3wA:9 a=CjuIK1q_8ugA:10 a=biEYGPWJfzWAr4FL6Ov7:22 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org 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... > + 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()? -Dave. -- Dave Chinner david@fromorbit.com