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=-2.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,T_DKIMWL_WL_HIGH,URIBL_BLOCKED, USER_AGENT_MUTT 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 EBB91C28CF6 for ; Sun, 29 Jul 2018 02:59:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A090A2089A for ; Sun, 29 Jul 2018 02:59:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="YZVpK3UA" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A090A2089A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726388AbeG2E2R (ORCPT ); Sun, 29 Jul 2018 00:28:17 -0400 Received: from mail.kernel.org ([198.145.29.99]:34356 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726016AbeG2E2R (ORCPT ); Sun, 29 Jul 2018 00:28:17 -0400 Received: from localhost (c-67-160-202-76.hsd1.ca.comcast.net [67.160.202.76]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 261292064D; Sun, 29 Jul 2018 02:59:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1532833171; bh=LL4FkVW9ySUyHIdIqgAhlpeGf+vS2piMdZjjnBdfDFw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=YZVpK3UAam8DTN1Pb7T4tcS4zdrNe1wCCiv4bBkxxtgxwIgNAZ4aUlLl1FYyRUb16 h2xCbTw4tMxRJ0506ta/CrxLYZh9EJZZOS7CWgLP71DfpI++BgwYTZ6Rx5B+TRGIDs Uk+o4UlYMgq3642bVygBERsSFXVw1JbV+ES1zHz0= Date: Sat, 28 Jul 2018 19:59:30 -0700 From: Jaegeuk Kim To: Chao Yu Cc: Chao Yu , linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org Subject: Re: [PATCH] f2fs: avoid race between zero_range and background GC Message-ID: <20180729025930.GA95148@jaegeuk-macbookpro.roam.corp.google.com> References: <20180726104536.114340-1-yuchao0@huawei.com> <20180727102916.GI16155@jaegeuk-macbookpro.roam.corp.google.com> <10d7814b-06d0-6751-ca56-85e7c8b92a27@kernel.org> <20180729020254.GH83620@jaegeuk-macbookpro.roam.corp.google.com> <6d86bad1-52fa-2309-9403-47490345e372@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6d86bad1-52fa-2309-9403-47490345e372@kernel.org> User-Agent: Mutt/1.8.2 (2017-04-18) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/29, Chao Yu wrote: > On 2018/7/29 10:02, Jaegeuk Kim wrote: > > On 07/27, Chao Yu wrote: > >> On 2018/7/27 18:29, Jaegeuk Kim wrote: > >>> On 07/26, Chao Yu wrote: > >>>> Thread A Background GC > >>>> - f2fs_zero_range > >>>> - truncate_pagecache_range > >>>> - gc_data_segment > >>>> - get_read_data_page > >>>> - move_data_page > >>>> - set_page_dirty > >>>> - set_cold_data > >>>> - f2fs_do_zero_range > >>>> - dn->data_blkaddr = NEW_ADDR; > >>>> - f2fs_set_data_blkaddr > >>>> > >>>> Actually, we don't need to set dirty & checked flag on the page, since > >>>> all valid data in the page should be zeroed by zero_range(). > >>> > >>> But, it doesn't matter too much, right? > >> > >> No, if the dirtied page is writebacked after f2fs_do_zero_range(), result of > >> zero_range() should be wrong, as zeroed page contains valid user data. > > > > How about truncating page caches after block address change or doing it twice > > before and after? > > Thread A Background GC > - f2fs_zero_range > - truncate_pagecache_range > - gc_data_segment > - get_read_data_page > - move_data_page > - set_page_dirty > - set_cold_data > - f2fs_do_zero_range > - dn->data_blkaddr = NEW_ADDR; > - f2fs_set_data_blkaddr > bdi-flusher > - __write_data_page > - f2fs_update_data_blkaddr > : data_blkaddr has been updated here. > - truncate_pagecache_range > : data & dnode has been writebacked before page cache truncation? > > How about this case? So, truncating pages under dnode lock can address it? > > Thanks, > > > > >> > >>> > >>>> Use i_gc_rwsem[WRITE] to avoid such race condition. > >>> > >>> Hope to avoid abusing i_gc_rwsem[] tho. > >> > >> Agreed, let's try avoiding until we have to use it. > >> > >> Thanks, > >> > >>> > >>>> > >>>> Signed-off-by: Chao Yu > >>>> --- > >>>> fs/f2fs/file.c | 2 ++ > >>>> 1 file changed, 2 insertions(+) > >>>> > >>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c > >>>> index 267ec3794e1e..7bd2412a8c37 100644 > >>>> --- a/fs/f2fs/file.c > >>>> +++ b/fs/f2fs/file.c > >>>> @@ -1309,6 +1309,7 @@ static int f2fs_zero_range(struct inode *inode, loff_t offset, loff_t len, > >>>> if (ret) > >>>> return ret; > >>>> > >>>> + down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]); > >>>> down_write(&F2FS_I(inode)->i_mmap_sem); > >>>> ret = filemap_write_and_wait_range(mapping, offset, offset + len - 1); > >>>> if (ret) > >>>> @@ -1389,6 +1390,7 @@ static int f2fs_zero_range(struct inode *inode, loff_t offset, loff_t len, > >>>> } > >>>> out_sem: > >>>> up_write(&F2FS_I(inode)->i_mmap_sem); > >>>> + up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]); > >>>> > >>>> return ret; > >>>> } > >>>> -- > >>>> 2.18.0.rc1