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=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 158EBC433E0 for ; Wed, 6 Jan 2021 09:09:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B5A5B2310B for ; Wed, 6 Jan 2021 09:09:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726606AbhAFJJl (ORCPT ); Wed, 6 Jan 2021 04:09:41 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:40563 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726501AbhAFJJk (ORCPT ); Wed, 6 Jan 2021 04:09:40 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1609924094; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=dYCgHYELd+dDiRR1ixtSQ94sasM6azspHhx1cz4I6fA=; b=XOpqjykzQkxstxtBML1OzliJzaKmzfbWULPgCnk2MaIY+B2AkCw2w1rLZ0LKGvmDQs3JoT UEZ9xJxJ4SJMtWu5lUbZitd9A1TfkMOr5Kai3mkc4T7NcGkaSXo9s/fsmTxDEPCYJcKTLV //MjkUtxlmwzDOnrysYMB+nWCgeHYcc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-278-om6WL-F3OhqV57fsaIrV2A-1; Wed, 06 Jan 2021 04:08:10 -0500 X-MC-Unique: om6WL-F3OhqV57fsaIrV2A-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A5DF7107ACE4; Wed, 6 Jan 2021 09:08:09 +0000 (UTC) Received: from T590 (ovpn-12-163.pek2.redhat.com [10.72.12.163]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B46EB7771A; Wed, 6 Jan 2021 09:08:03 +0000 (UTC) Date: Wed, 6 Jan 2021 17:07:58 +0800 From: Ming Lei To: Mauricio Faria de Oliveira Cc: Jens Axboe , linux-block@vger.kernel.org, Gabriel Krisman Bertazi , Eric Desrochers Subject: Re: [PATCH v2] loop: fix I/O error on fsync() in detached loop devices Message-ID: <20210106090758.GB3845805@T590> References: <20210105135419.68715-1-mfo@canonical.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210105135419.68715-1-mfo@canonical.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Tue, Jan 05, 2021 at 10:54:19AM -0300, Mauricio Faria de Oliveira wrote: > There's an I/O error on fsync() in a detached loop device > if it has been previously attached. > > The issue is write cache is enabled in the attach path in > loop_configure() but it isn't disabled in the detach path; > thus it remains enabled in the block device regardless of > whether it is attached or not. > > Now fsync() can get an I/O request that will just be failed > later in loop_queue_rq() as device's state is not 'Lo_bound'. > > So, disable write cache in the detach path. > > Test-case: > > # DEV=/dev/loop7 > > # IMG=/tmp/image > # truncate --size 1M $IMG > > # losetup $DEV $IMG > # losetup -d $DEV > > Before: > > # strace -e fsync parted -s $DEV print 2>&1 | grep fsync > fsync(3) = -1 EIO (Input/output error) > Warning: Error fsyncing/closing /dev/loop7: Input/output error > [ 982.529929] blk_update_request: I/O error, dev loop7, sector 0 op 0x1:(WRITE) flags 0x800 phys_seg 0 prio class 0 > > After: > > # strace -e fsync parted -s $DEV print 2>&1 | grep fsync > fsync(3) = 0 But IO on detached loop should have been failed, right? The magic is that submit_bio_checks() filters FLUSH request for queues which doesn't support writeback cache, and always fake a normal completion. I understand that the issue is that user becomes confused with this observation because no such failure if they run 'parted -s /dev/loop0 print' on one detached loop disk if it is never attached. Thanks, Ming