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 BAE70C00140 for ; Mon, 8 Aug 2022 10:26:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242121AbiHHK0T (ORCPT ); Mon, 8 Aug 2022 06:26:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47136 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235610AbiHHK0R (ORCPT ); Mon, 8 Aug 2022 06:26:17 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id B8BE4EAF for ; Mon, 8 Aug 2022 03:26:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1659954374; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=bdXQa3jk2tERG3z0xEmPh3dxhv9AB24nx7bC8R2QZ+M=; b=e0Knku5rtRYbjtWVHOi6i7VBBWcsgRIR4CQ/F1u7e6xEFz2G9ZTRxWiyL5/uTMND8uxE46 EK9dmeiaXAEC7DkJUj4V+Prc2CFj1wWiFEoKnBJTncoRHS3PG8oVcCzr6ZIWeyqj1rgc/3 e0i7SsVWrSLe/7Lp9IUdM58Yqg/78pI= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-147-c696xEXwMfeok6kgVayt9g-1; Mon, 08 Aug 2022 06:26:11 -0400 X-MC-Unique: c696xEXwMfeok6kgVayt9g-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 39B6E108C0DE; Mon, 8 Aug 2022 10:26:09 +0000 (UTC) Received: from fedora (unknown [10.40.192.32]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0B78B40C1241; Mon, 8 Aug 2022 10:26:07 +0000 (UTC) Date: Mon, 8 Aug 2022 12:26:05 +0200 From: Lukas Czerner To: Dave Chinner Cc: linux-ext4@vger.kernel.org, jlayton@kernel.org, tytso@mit.edu, linux-fsdevel@vger.kernel.org, Christoph Hellwig , Jan Kara Subject: Re: [PATCH v2 2/3] fs: record I_DIRTY_TIME even if inode already has I_DIRTY_INODE Message-ID: <20220808102605.racoct6amqn55uqc@fedora> References: <20220803105340.17377-1-lczerner@redhat.com> <20220803105340.17377-2-lczerner@redhat.com> <20220807230810.GF3861211@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220807230810.GF3861211@dread.disaster.area> X-Scanned-By: MIMEDefang 2.84 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Mon, Aug 08, 2022 at 09:08:10AM +1000, Dave Chinner wrote: > On Wed, Aug 03, 2022 at 12:53:39PM +0200, Lukas Czerner wrote: > > Currently the I_DIRTY_TIME will never get set if the inode already has > > I_DIRTY_INODE with assumption that it supersedes I_DIRTY_TIME. That's > > true, however ext4 will only update the on-disk inode in > > ->dirty_inode(), not on actual writeback. As a result if the inode > > already has I_DIRTY_INODE state by the time we get to > > __mark_inode_dirty() only with I_DIRTY_TIME, the time was already filled > > into on-disk inode and will not get updated until the next I_DIRTY_INODE > > update, which might never come if we crash or get a power failure. > > > > The problem can be reproduced on ext4 by running xfstest generic/622 > > with -o iversion mount option. > > > > Fix it by allowing I_DIRTY_TIME to be set even if the inode already has > > I_DIRTY_INODE. Also make sure that the case is properly handled in > > writeback_single_inode() as well. Additionally changes in > > xfs_fs_dirty_inode() was made to accommodate for I_DIRTY_TIME in flag. > > > > Thanks Jan Kara for suggestions on how to make this work properly. > > > > Cc: Dave Chinner > > Cc: Christoph Hellwig > > Signed-off-by: Lukas Czerner > > Suggested-by: Jan Kara > > --- > > v2: Reworked according to suggestions from Jan > > .... > > > diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c > > index aa977c7ea370..cff05a4771b5 100644 > > --- a/fs/xfs/xfs_super.c > > +++ b/fs/xfs/xfs_super.c > > @@ -658,7 +658,8 @@ xfs_fs_dirty_inode( > > > > if (!(inode->i_sb->s_flags & SB_LAZYTIME)) > > return; > > - if (flag != I_DIRTY_SYNC || !(inode->i_state & I_DIRTY_TIME)) > > + if ((flag & ~I_DIRTY_TIME) != I_DIRTY_SYNC || > > + !((inode->i_state | flag) & I_DIRTY_TIME)) > > return; > > My eyes, they bleed. The dirty time code was already a horrid > abomination, and this makes it worse. > > From looking at the code, I cannot work out what the new semantics > for I_DIRTY_TIME and I_DIRTY_SYNC are supposed to be, nor can I work Hi Dave, please see the other thready for this patch with Eric Biggers, where I try to explain and give some suggestion to change the doc. Does it make sense to you, or am I missing something? https://marc.info/?l=linux-ext4&m=165970194205621&w=2 > out what the condition this is new code is supposed to be doing. I > *can't verify it is correct* by reading the code. The ->dirty_inode() needed to be changed to clear I_DIRTY_TIME from i_state *before* we call ->dirty_inode() to avoid race where we would lose timestamp update that comes just a little later, after -dirty_inode() call with I_DRITY_INODE. But that would break xfs, so I decided to keep the condition and loosen the requirement so that I_DIRTY_TIME can also be se in 'flag', not just the i_state. Hence the abomination. > > Can you please add a comment here explaining the conditions where we > don't have to log a new timestamp update? How about something like this? Only do the timestamp update if the inode is dirty (I_DIRTY_SYNC) and has dirty timestamp (I_DIRTY_TIME). I_DIRTY_TIME can be either already set in i_state, or passed in flags possibly together with I_DIRTY_SYNC. > > Also, if "flag" now contains multiple flags, can you rename it > "flags"? Sure, I can do that. Thanks! -Lukas > > Cheers, > > Dave. > > -- > Dave Chinner > david@fromorbit.com >