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 66F10CA9EB7 for ; Mon, 21 Oct 2019 19:43:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4084920882 for ; Mon, 21 Oct 2019 19:43:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730191AbfJUTni (ORCPT ); Mon, 21 Oct 2019 15:43:38 -0400 Received: from mx2.suse.de ([195.135.220.15]:49012 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728543AbfJUTni (ORCPT ); Mon, 21 Oct 2019 15:43:38 -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 36404AD72; Mon, 21 Oct 2019 19:43:32 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 1A2AF1E4AA2; Mon, 21 Oct 2019 21:43:30 +0200 (CEST) Date: Mon, 21 Oct 2019 21:43:30 +0200 From: Jan Kara To: "Theodore Y. Ts'o" Cc: Matthew Bobrowski , jack@suse.cz, 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: <20191021194330.GJ25184@quack2.suse.cz> References: <20191021133111.GA4675@mit.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191021133111.GA4675@mit.edu> 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 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? Honza -- Jan Kara SUSE Labs, CR