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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 645E8C04A68 for ; Wed, 27 Jul 2022 09:20:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231657AbiG0JUi (ORCPT ); Wed, 27 Jul 2022 05:20:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33474 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231667AbiG0JU2 (ORCPT ); Wed, 27 Jul 2022 05:20:28 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 66F5013E93 for ; Wed, 27 Jul 2022 02:20:26 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.53]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4Lt7Vx6bLyzmVBd; Wed, 27 Jul 2022 17:18:33 +0800 (CST) Received: from [10.174.177.76] (10.174.177.76) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Wed, 27 Jul 2022 17:20:13 +0800 Subject: Re: [RFC PATCH v4 4/8] hugetlbfs: catch and handle truncate racing with page faults To: Mike Kravetz , , CC: Muchun Song , Michal Hocko , Peter Xu , Naoya Horiguchi , David Hildenbrand , "Aneesh Kumar K . V" , Andrea Arcangeli , "Kirill A . Shutemov" , Davidlohr Bueso , Prakash Sangappa , James Houghton , Mina Almasry , Pasha Tatashin , Axel Rasmussen , Ray Fucillo , Andrew Morton References: <20220706202347.95150-1-mike.kravetz@oracle.com> <20220706202347.95150-5-mike.kravetz@oracle.com> From: Miaohe Lin Message-ID: Date: Wed, 27 Jul 2022 17:20:12 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20220706202347.95150-5-mike.kravetz@oracle.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/7/7 4:23, Mike Kravetz wrote: > Most hugetlb fault handling code checks for faults beyond i_size. > While there are early checks in the code paths, the most difficult > to handle are those discovered after taking the page table lock. > At this point, we have possibly allocated a page and consumed > associated reservations and possibly added the page to the page cache. > > When discovering a fault beyond i_size, be sure to: > - Remove the page from page cache, else it will sit there until the > file is removed. > - Do not restore any reservation for the page consumed. Otherwise > there will be an outstanding reservation for an offset beyond the > end of file. > > The 'truncation' code in remove_inode_hugepages must deal with fault > code potentially removing a page/folio from the cache after the page was > returned by filemap_get_folios and before locking the page. This can be > discovered by a change in folio_mapping() after taking folio lock. In > addition, this code must deal with fault code potentially consuming > and returning reservations. To synchronize this, remove_inode_hugepages > will now take the fault mutex for ALL indices in the hole or truncated > range. In this way, it KNOWS fault code has finished with the page/index > OR fault code will see the updated file size. > > Signed-off-by: Mike Kravetz > --- > @@ -5606,8 +5610,10 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm, > > ptl = huge_pte_lock(h, mm, ptep); > size = i_size_read(mapping->host) >> huge_page_shift(h); > - if (idx >= size) > + if (idx >= size) { > + beyond_i_size = true; Thanks for your patch. There is one question: Since races between hugetlb pagefault and truncate is guarded by hugetlb_fault_mutex, do we really need to check it again after taking the page table lock? BTW: I will learn more about this series when I have enough time. Thanks for your work. :)