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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, 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 70D1DC54FCC for ; Mon, 20 Apr 2020 22:19:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 534F920722 for ; Mon, 20 Apr 2020 22:19:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726056AbgDTWTN (ORCPT ); Mon, 20 Apr 2020 18:19:13 -0400 Received: from mail105.syd.optusnet.com.au ([211.29.132.249]:58197 "EHLO mail105.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725774AbgDTWTM (ORCPT ); Mon, 20 Apr 2020 18:19:12 -0400 Received: from dread.disaster.area (pa49-180-0-232.pa.nsw.optusnet.com.au [49.180.0.232]) by mail105.syd.optusnet.com.au (Postfix) with ESMTPS id C99353A3FE0; Tue, 21 Apr 2020 08:19:09 +1000 (AEST) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1jQeku-0006KG-Q2; Tue, 21 Apr 2020 08:19:08 +1000 Date: Tue, 21 Apr 2020 08:19:08 +1000 From: Dave Chinner To: Brian Foster Cc: linux-xfs@vger.kernel.org Subject: Re: [PATCH 01/12] xfs: refactor failed buffer resubmission into xfsaild Message-ID: <20200420221908.GO9800@dread.disaster.area> References: <20200417150859.14734-1-bfoster@redhat.com> <20200417150859.14734-2-bfoster@redhat.com> <20200420024556.GD9800@dread.disaster.area> <20200420135825.GA27516@bfoster> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200420135825.GA27516@bfoster> User-Agent: Mutt/1.10.1 (2018-07-13) X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.3 cv=W5xGqiek c=1 sm=1 tr=0 a=XYjVcjsg+1UI/cdbgX7I7g==:117 a=XYjVcjsg+1UI/cdbgX7I7g==:17 a=kj9zAlcOel0A:10 a=cl8xLZFz6L8A:10 a=20KFwNOVAAAA:8 a=7-415B0cAAAA:8 a=MzdJU4Orhpkszo7Ei48A:9 a=CjuIK1q_8ugA:10 a=biEYGPWJfzWAr4FL6Ov7:22 Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Mon, Apr 20, 2020 at 09:58:25AM -0400, Brian Foster wrote: > On Mon, Apr 20, 2020 at 12:45:56PM +1000, Dave Chinner wrote: > > On Fri, Apr 17, 2020 at 11:08:48AM -0400, Brian Foster wrote: > > > Flush locked log items whose underlying buffers fail metadata > > > writeback are tagged with a special flag to indicate that the flush > > > lock is already held. This is currently implemented in the type > > > specific ->iop_push() callback, but the processing required for such > > > items is not type specific because we're only doing basic state > > > management on the underlying buffer. > > > > > > Factor the failed log item handling out of the inode and dquot > > > ->iop_push() callbacks and open code the buffer resubmit helper into > > > a single helper called from xfsaild_push_item(). This provides a > > > generic mechanism for handling failed metadata buffer writeback with > > > a bit less code. > > > > > > Signed-off-by: Brian Foster > > ..... > > > diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c > > > index 564253550b75..0c709651a2c6 100644 > > > --- a/fs/xfs/xfs_trans_ail.c > > > +++ b/fs/xfs/xfs_trans_ail.c > > > @@ -345,6 +345,45 @@ xfs_ail_delete( > > > xfs_trans_ail_cursor_clear(ailp, lip); > > > } > > > > > > +/* > > > + * Requeue a failed buffer for writeback. > > > + * > > > + * We clear the log item failed state here as well, but we have to be careful > > > + * about reference counts because the only active reference counts on the buffer > > > + * may be the failed log items. Hence if we clear the log item failed state > > > + * before queuing the buffer for IO we can release all active references to > > > + * the buffer and free it, leading to use after free problems in > > > + * xfs_buf_delwri_queue. It makes no difference to the buffer or log items which > > > + * order we process them in - the buffer is locked, and we own the buffer list > > > + * so nothing on them is going to change while we are performing this action. > > > + * > > > + * Hence we can safely queue the buffer for IO before we clear the failed log > > > + * item state, therefore always having an active reference to the buffer and > > > + * avoiding the transient zero-reference state that leads to use-after-free. > > > + */ > > > +static inline int > > > +xfsaild_push_failed( > > > > Bad name IMO. Makes me think it's an action that is taken when an > > item push failed, not an action that resubmits a buffer that had an > > IO failure. > > > > i.e. "push" doesn't imply IO, and failure to push an item doesn't > > mean there was an IO error - it may be locked, already flushing, > > pinned, etc. > > > > Yeah.. > > > > + struct xfs_log_item *lip, > > > + struct list_head *buffer_list) > > > +{ > > > + struct xfs_buf *bp = lip->li_buf; > > > > This also assumes that the log item has a buffer associated with it. > > So perhaps "xfsaild_resubmit_failed_buffer()" would be more > > approriate here. > > > > The buffer pointer is an implementation detail of failed items. It would > be nice to find a way to avoid that. How about xfsaild_resubmit_item() > to be consistent with the parent function (xfsaild_push_item())? That works, too. :) Cheers, Dave. -- Dave Chinner david@fromorbit.com