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=-6.7 required=3.0 tests=FORGED_MUA_MOZILLA, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 E82E8C432C0 for ; Thu, 28 Nov 2019 10:20:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C594421774 for ; Thu, 28 Nov 2019 10:20:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726520AbfK1KUn (ORCPT ); Thu, 28 Nov 2019 05:20:43 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:8268 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726227AbfK1KUm (ORCPT ); Thu, 28 Nov 2019 05:20:42 -0500 Received: from pps.filterd (m0098394.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id xASAHaeD119980 for ; Thu, 28 Nov 2019 05:20:42 -0500 Received: from e06smtp01.uk.ibm.com (e06smtp01.uk.ibm.com [195.75.94.97]) by mx0a-001b2d01.pphosted.com with ESMTP id 2whcxrwbt2-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 28 Nov 2019 05:20:42 -0500 Received: from localhost by e06smtp01.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Thu, 28 Nov 2019 10:20:36 -0000 Received: from d06av21.portsmouth.uk.ibm.com (d06av21.portsmouth.uk.ibm.com [9.149.105.232]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id xASAKZFA66322460 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 28 Nov 2019 10:20:35 GMT Received: from d06av21.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6525152054; Thu, 28 Nov 2019 10:20:35 +0000 (GMT) Received: from localhost.localdomain (unknown [9.85.87.233]) by d06av21.portsmouth.uk.ibm.com (Postfix) with ESMTP id 6085952057; Thu, 28 Nov 2019 10:20:32 +0000 (GMT) Subject: Re: [PATCH] f2fs: Fix direct IO handling To: Damien Le Moal , "linux-f2fs-devel@lists.sourceforge.net" , "linux-kernel@vger.kernel.org" , Jaegeuk Kim , Chao Yu Cc: "linux-fsdevel@vger.kernel.org" , Javier Gonzalez , Shinichiro Kawasaki References: <20191126075719.1046485-1-damien.lemoal@wdc.com> <20191126083443.F1FD5A405B@b06wcsmtp001.portsmouth.uk.ibm.com> From: Ritesh Harjani Date: Thu, 28 Nov 2019 15:50:30 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 19112810-4275-0000-0000-0000038770F9 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19112810-4276-0000-0000-0000389B0254 Message-Id: <20191128102033.6085952057@d06av21.portsmouth.uk.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.95,18.0.572 definitions=2019-11-28_01:2019-11-28,2019-11-28 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 clxscore=1015 impostorscore=0 mlxlogscore=999 suspectscore=0 priorityscore=1501 spamscore=0 phishscore=0 lowpriorityscore=0 malwarescore=0 mlxscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1910280000 definitions=main-1911280089 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 11/28/19 7:40 AM, Damien Le Moal wrote: > On 2019/11/26 17:34, Ritesh Harjani wrote: >> Hello Damien, >> >> IIUC, you are trying to fix a stale data read by DIO read for the case >> you explained in your patch w.r.t. DIO-write forced to write as buffIO. >> >> Coincidentally I was just looking at the same code path just now. >> So I do have a query to you/f2fs group. Below could be silly one, as I >> don't understand F2FS in great detail. >> >> How is the stale data by DIO read, is protected against a mmap >> writes via f2fs_vm_page_mkwrite? >> >> f2fs_vm_page_mkwrite() f2fs_direct_IO (read) >> filemap_write_and_wait_range() >> -> f2fs_get_blocks() >> -> submit_bio() >> >> -> set_page_dirty() >> >> Is above race possible with current f2fs code? >> i.e. f2fs_direct_IO could read the stale data from the blocks >> which were allocated due to mmap fault? > > The faulted page is locked until the fault is fully processed so direct > IO has to wait for that to complete first. How about below parallelism? f2fs_vm_page_mkwrite() f2fs_direct_IO (read) filemap_write_and_wait_range() -> down_read(->i_mmap_sem); -> lock_page() -> f2fs_get_blocks() -> submit_bio() -> set_page_dirty() Can above DIO read not expose the stale data from block which was allocated in f2fs_vm_page_mkwrite path? > >> >> Am I missing something here? >> >> -ritesh >> >> On 11/26/19 1:27 PM, Damien Le Moal wrote: >>> f2fs_preallocate_blocks() identifies direct IOs using the IOCB_DIRECT >>> flag for a kiocb structure. However, the file system direct IO handler >>> function f2fs_direct_IO() may have decided that a direct IO has to be >>> exececuted as a buffered IO using the function f2fs_force_buffered_io(). >>> This is the case for instance for volumes including zoned block device >>> and for unaligned write IOs with LFS mode enabled. >>> >>> These 2 different methods of identifying direct IOs can result in >>> inconsistencies generating stale data access for direct reads after a >>> direct IO write that is treated as a buffered write. Fix this >>> inconsistency by combining the IOCB_DIRECT flag test with the result >>> of f2fs_force_buffered_io(). >>> >>> Reported-by: Javier Gonzalez >>> Signed-off-by: Damien Le Moal >>> --- >>> fs/f2fs/data.c | 4 +++- >>> 1 file changed, 3 insertions(+), 1 deletion(-) >>> >>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c >>> index 5755e897a5f0..8ac2d3b70022 100644 >>> --- a/fs/f2fs/data.c >>> +++ b/fs/f2fs/data.c >>> @@ -1073,6 +1073,8 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from) >>> int flag; >>> int err = 0; >>> bool direct_io = iocb->ki_flags & IOCB_DIRECT; >>> + bool do_direct_io = direct_io && >>> + !f2fs_force_buffered_io(inode, iocb, from); >>> >>> /* convert inline data for Direct I/O*/ >>> if (direct_io) { >>> @@ -1081,7 +1083,7 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from) >>> return err; >>> } >>> >>> - if (direct_io && allow_outplace_dio(inode, iocb, from)) >>> + if (do_direct_io && allow_outplace_dio(inode, iocb, from)) >>> return 0; >>> >>> if (is_inode_flag_set(inode, FI_NO_PREALLOC)) >>> >> >> > >