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 85D7EC46461 for ; Mon, 30 Jul 2018 01:38:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2D8BC20893 for ; Mon, 30 Jul 2018 01:38:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="UhfRzcAj" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2D8BC20893 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 S1728801AbeG3DKw (ORCPT ); Sun, 29 Jul 2018 23:10:52 -0400 Received: from mail.kernel.org ([198.145.29.99]:54108 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728628AbeG3DKw (ORCPT ); Sun, 29 Jul 2018 23:10:52 -0400 Received: from localhost (unknown [104.132.1.88]) (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 09FBE20873; Mon, 30 Jul 2018 01:38:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1532914697; bh=Cke4JUXL27dk3AQKmfLNhnABuTQubcUwRqeJsBMqEiY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=UhfRzcAjxldv9iSFm6U6a/9Irh34x79TWF2wcBNPJwszFbQFXPBeDb8aqPBBeP4P/ XbMLcMOFxuOl0w87kkkd0b4aTZJjtSHC8ovqxFa8sztmgRiI1uDb2siTDXGGLFY5pg 9jtfW4p+73qZ4BZoW/em8fg65vURszllijDwgTqM= Date: Sun, 29 Jul 2018 18:38:16 -0700 From: Jaegeuk Kim To: Chao Yu Cc: linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net Subject: Re: [f2fs-dev] [PATCH] f2fs: avoid race between zero_range and background GC Message-ID: <20180730013816.GA15708@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> <20180729025930.GA95148@jaegeuk-macbookpro.roam.corp.google.com> <20180729051459.GB97518@jaegeuk-macbookpro.roam.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180729051459.GB97518@jaegeuk-macbookpro.roam.corp.google.com> 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 07/28, Jaegeuk Kim wrote: > On 07/29, Chao Yu wrote: > > On 2018/7/29 10:59, Jaegeuk Kim wrote: > > > 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? > > > > Normally, our lock dependency is > > > > ->writepage() > > lock data page -> lock dnode page > > > > here > > lock dnode page -> truncate_pagecache_range::lock data page > > > > Will easily cause deadlock? > > Yeah. Can we add an inode flag to bypass GC in this case, then? Hmm, BTW, how about using i_gc_rwsem[WRITE] in a very narrow scope? for (index = pg_start; index < pg_end;) { f2fs_lock_op(); down_write(i_gc_rwsem[WRITE]); truncate_page_cache_range(index, index + 4k); f2fs_do_zero_range(&dn, index, end); up_write(i_gc_rwsem[WRITE]); f2fs_unlock_op(); f2fs_balance_fs(); } > > > > > Thanks, > > > > > > > >> > > >> 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 > > ------------------------------------------------------------------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > _______________________________________________ > Linux-f2fs-devel mailing list > Linux-f2fs-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel