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,URIBL_BLOCKED,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 1CD70CA9EB9 for ; Wed, 23 Oct 2019 10:01:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F143020650 for ; Wed, 23 Oct 2019 10:01:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404288AbfJWKB5 (ORCPT ); Wed, 23 Oct 2019 06:01:57 -0400 Received: from mx2.suse.de ([195.135.220.15]:48046 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2390361AbfJWKB4 (ORCPT ); Wed, 23 Oct 2019 06:01:56 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id F32D2AF19; Wed, 23 Oct 2019 10:01:53 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 705B41E4A89; Wed, 23 Oct 2019 12:01:53 +0200 (CEST) Date: Wed, 23 Oct 2019 12:01:53 +0200 From: Jan Kara To: Matthew Bobrowski Cc: Jan Kara , "Theodore Y. Ts'o" , adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, hch@infradead.org, david@fromorbit.com, darrick.wong@oracle.com Subject: Re: [PATCH v5 00/12] ext4: port direct I/O to iomap infrastructure Message-ID: <20191023100153.GB22307@quack2.suse.cz> References: <20191021133111.GA4675@mit.edu> <20191021194330.GJ25184@quack2.suse.cz> <20191023023519.GA16505@bobrowski> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191023023519.GA16505@bobrowski> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed 23-10-19 13:35:19, Matthew Bobrowski wrote: > On Mon, Oct 21, 2019 at 09:43:30PM +0200, Jan Kara wrote: > > On Mon 21-10-19 09:31:12, Theodore Y. Ts'o wrote: > > > Hi Matthew, thanks for your work on this patch series! > > > > > > I applied it against 4c3, and ran a quick test run on it, and found > > > the following locking problem. To reproduce: > > > > > > kvm-xfstests -c nojournal generic/113 > > > > > > generic/113 [09:27:19][ 5.841937] run fstests generic/113 at 2019-10-21 09:27:19 > > > [ 7.959477] > > > [ 7.959798] ============================================ > > > [ 7.960518] WARNING: possible recursive locking detected > > > [ 7.961225] 5.4.0-rc3-xfstests-00012-g7fe6ea084e48 #1238 Not tainted > > > [ 7.961991] -------------------------------------------- > > > [ 7.962569] aio-stress/1516 is trying to acquire lock: > > > [ 7.963129] ffff9fd4791148c8 (&sb->s_type->i_mutex_key#12){++++}, at: __generic_file_fsync+0x3e/0xb0 > > > [ 7.964109] > > > [ 7.964109] but task is already holding lock: > > > [ 7.964740] ffff9fd4791148c8 (&sb->s_type->i_mutex_key#12){++++}, at: ext4_dio_write_iter+0x15b/0x430 > > > > This is going to be a tricky one. With iomap, the inode locking is handled > > by the filesystem while calling generic_write_sync() is done by > > iomap_dio_rw(). I would really prefer to avoid tweaking iomap_dio_rw() not > > to call generic_write_sync(). So we need to remove inode_lock from > > __generic_file_fsync() (used from ext4_sync_file()). This locking is mostly > > for legacy purposes and we don't need this in ext4 AFAICT - but removing > > the lock from __generic_file_fsync() would mean auditing all legacy > > filesystems that use this to make sure flushing inode & its metadata buffer > > list while it is possibly changing cannot result in something unexpected. I > > don't want to clutter this series with it so we are left with > > reimplementing __generic_file_fsync() inside ext4 without inode_lock. Not > > too bad but not great either. Thoughts? > > So, I just looked at this on my lunch break and I think the simplest > approach would be to just transfer the necessary chunks of code from > within __generic_file_fsync() into ext4_sync_file() for !journal cases, > minus the inode lock, and minus calling into __generic_file_fsync(). I > don't forsee this causing any issues, but feel free to correct me if I'm > wrong. Yes, that's what I'd suggest as well. In fact when doing that you can share file_write_and_wait_range() call with the one already in ext4_sync_file() use for other cases. Similarly with file_check_and_advance_wb_err(). So the copied bit will be really only: ret = sync_mapping_buffers(inode->i_mapping); if (!(inode->i_state & I_DIRTY_ALL)) goto out; if (datasync && !(inode->i_state & I_DIRTY_DATASYNC)) goto out; err = sync_inode_metadata(inode, 1); if (ret == 0) ret = err; > If this is deemed to be OK, then I will go ahead and include this as a > separate patch in my series. Yes, please. Honza -- Jan Kara SUSE Labs, CR