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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 85F40C433E0 for ; Mon, 25 May 2020 07:45:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 67BDB20679 for ; Mon, 25 May 2020 07:45:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389183AbgEYHpO (ORCPT ); Mon, 25 May 2020 03:45:14 -0400 Received: from mx2.suse.de ([195.135.220.15]:38182 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389105AbgEYHpO (ORCPT ); Mon, 25 May 2020 03:45:14 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id A4B95ABEC; Mon, 25 May 2020 07:45:14 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id E45311E1270; Mon, 25 May 2020 09:38:35 +0200 (CEST) Date: Mon, 25 May 2020 09:38:35 +0200 From: Jan Kara To: Hillf Danton Cc: Martijn Coenen , Al Viro , Jan Kara , Jens Axboe , miklos@szeredi.hu, tj@kernel.org, linux-fsdevel@vger.kernel.org, LKML , android-storage-core@google.com, kernel-team@android.com Subject: Re: Writeback bug causing writeback stalls Message-ID: <20200525073835.GJ14199@quack2.suse.cz> References: <20200524140522.14196-1-hdanton@sina.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200524140522.14196-1-hdanton@sina.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun 24-05-20 22:05:22, Hillf Danton wrote: > > On Fri, 22 May 2020 11:57:42 +0200 Martijn Coenen wrote: > > > > So, the sequence of events is something like this. Let's assume the inode is > > already on b_dirty_time for valid reasons. Then: > > > > CPU1 CPU2 > > fuse_flush() > > write_inode_now() > > writeback_single_inode() > > sets I_SYNC > > __writeback_single_inode() > > writes back data > > clears inode dirty flags > > unlocks inode > > calls mark_inode_dirty_sync() > > sets I_DIRTY_SYNC, but doesn't > > update wb list because I_SYNC is > > still set > > write() // somebody else writes > > mark_inode_dirty(I_DIRTY_PAGES) > > sets I_DIRTY_PAGES on i_state > > doesn't update wb list, > > because I_SYNC set > > locks inode again > > sees inode is still dirty, > > doesn't touch WB list > > clears I_SYNC > > > > So now we have an inode on b_dirty_time with I_DIRTY_PAGES | I_DIRTY_SYNC set, > > and subsequent calls to mark_inode_dirty() with either I_DIRTY_PAGES or > > I_DIRTY_SYNC will do nothing to change that. The flusher won't touch > > the inode either, because it's not on a b_dirty or b_io list. Hi Hillf, > Based on the above analysis, check of I_DIRTY_TIME is added before and > after calling __writeback_single_inode() to detect the case you reported. > > If a dirty inode is not on the right io list after writeback, we can > move it to a new one; and we can do that as we are the I_SYNC owner. > > While changing its io list, the inode's dirty timestamp is also updated > to the current tick as does in __mark_inode_dirty(). Apparently you didn't read my reply to Martinj because what you did in this patch is exactly what I described that we cannot do because that can cause sync(2) to miss inodes and thus break its data integrity guarantees. So we have to come up with a different solution. Honza > --- a/fs/fs-writeback.c > +++ b/fs/fs-writeback.c > @@ -1528,6 +1528,7 @@ static int writeback_single_inode(struct > struct writeback_control *wbc) > { > struct bdi_writeback *wb; > + bool dt; > int ret = 0; > > spin_lock(&inode->i_lock); > @@ -1560,6 +1561,7 @@ static int writeback_single_inode(struct > !mapping_tagged(inode->i_mapping, PAGECACHE_TAG_WRITEBACK))) > goto out; > inode->i_state |= I_SYNC; > + dt = inode->i_state & I_DIRTY_TIME; > wbc_attach_and_unlock_inode(wbc, inode); > > ret = __writeback_single_inode(inode, wbc); > @@ -1574,6 +1576,14 @@ static int writeback_single_inode(struct > */ > if (!(inode->i_state & I_DIRTY_ALL)) > inode_io_list_del_locked(inode, wb); > + else if (!(inode->i_state & I_DIRTY_TIME) && dt) { > + /* > + * We can correct inode's io list, however, by moving it to > + * b_dirty from b_dirty_time as we are the I_SYNC owner > + */ > + inode->dirtied_when = jiffies; > + inode_io_list_move_locked(inode, wb, &wb->b_dirty); > + } > spin_unlock(&wb->list_lock); > inode_sync_complete(inode); > out: > -- > -- Jan Kara SUSE Labs, CR