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=-2.3 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 A7450CA9EB9 for ; Tue, 22 Oct 2019 08:40:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8872A2089E for ; Tue, 22 Oct 2019 08:40:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388469AbfJVIk0 (ORCPT ); Tue, 22 Oct 2019 04:40:26 -0400 Received: from mx2.suse.de ([195.135.220.15]:52332 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2388366AbfJVIk0 (ORCPT ); Tue, 22 Oct 2019 04:40:26 -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 C3643AB92; Tue, 22 Oct 2019 08:40:23 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 277AC1E4AA7; Tue, 22 Oct 2019 10:01:42 +0200 (CEST) Date: Tue, 22 Oct 2019 10:01:42 +0200 From: Jan Kara To: Dave Chinner Cc: Jan Kara , "Theodore Y. Ts'o" , Matthew Bobrowski , adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, hch@infradead.org, darrick.wong@oracle.com Subject: Re: [PATCH v5 00/12] ext4: port direct I/O to iomap infrastructure Message-ID: <20191022080142.GC2436@quack2.suse.cz> References: <20191021133111.GA4675@mit.edu> <20191021194330.GJ25184@quack2.suse.cz> <20191021223819.GB2642@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191021223819.GB2642@dread.disaster.area> 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 Tue 22-10-19 09:38:19, Dave Chinner 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(). > > You can't remove it from there, because that will break O_DSYNC > AIO+DIO. i.e. generic_write_sync() needs to be called before > iocb->ki_complete() is called in the AIO completion path, and that > means filesystems using iomap_dio_rw need to be be able to run > generic_write_sync() without taking the inode_lock(). > > > 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? > > XFS has implemented it's own ->fsync operation pretty much forever > without issues. It's basically: > > 1. flush dirty cached data w/ WB_SYNC_ALL > 2. flush dirty cached metadata (i.e. journal force) > 3. flush device caches if journal force didn't, keeping in > mind the requirements of data and journal being placed on > different devices. > > The ext4 variant shouldn't need to be any more complex than that... Yeah, that's what we do for the common case as well. But when the filesystem is created without a journal (i.e., ext2 compatibility mode) we currently use the old fsync implementation including __generic_file_fsync(). But as I wrote above, duplicating those ~5 lines out of __generic_file_fsync() we really care about is not a big deal. Honza -- Jan Kara SUSE Labs, CR