From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from caladan.c-14.de ([78.47.48.217]:35326 "EHLO Caladan.localdomain" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751521AbaIFVBN (ORCPT ); Sat, 6 Sep 2014 17:01:13 -0400 Received: from localhost (HSI-KBW-109-193-071-016.hsi7.kabel-badenwuerttemberg.de [109.193.71.16]) by Caladan.localdomain (Postfix) with ESMTPSA id 854FB764D3 for ; Sat, 6 Sep 2014 20:54:19 +0000 (UTC) Date: Sat, 6 Sep 2014 22:54:17 +0200 From: Simon Thelen To: linux-btrfs@vger.kernel.org Subject: Cannot remount root subvolume read-only. Message-ID: <20140906205417.GA1919@anonymous> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: Hello, Whenever I try to remount the root subvolume of my btrfs filesystem as read-only `mount -o remount,ro /', I get an error 'mount: / is busy' and the first time I execute the command I also get the following stack trace in dmesg: [ +0.724055] ------------[ cut here ]------------ [ +0.000011] WARNING: CPU: 2 PID: 711 at fs/sync.c:55 sync_filesystem+0x97/0xa0() [ +0.000002] Modules linked in: snd_hda_codec_idt snd_hda_codec_hdmi snd_hda_codec_generic snd_hda_intel snd_hda_controller wmi snd_hda_codec snd_hwdep [ +0.000012] CPU: 2 PID: 711 Comm: mount Tainted: G I 3.16.1-gentoo #1 [ +0.000002] Hardware name: Hewlett-Packard HP ENVY 17 Notebook PC/1966, BIOS F.11 04/19/2013 [ +0.000002] 0000000000000009 ffff880252467c60 ffffffff81852400 0000000000000000 [ +0.000004] ffff880252467c98 ffffffff810a3488 ffff88007fbf2000 0000000000000001 [ +0.000003] 0000000070808001 ffff8802551c9000 ffff880252467dcc ffff880252467ca8 [ +0.000003] Call Trace: [ +0.000010] [] dump_stack+0x45/0x56 [ +0.000006] [] warn_slowpath_common+0x78/0xa0 [ +0.000004] [] warn_slowpath_null+0x15/0x20 [ +0.000003] [] sync_filesystem+0x97/0xa0 [ +0.000007] [] btrfs_remount+0x7e/0x4c0 [ +0.000007] [] ? free_pages.part.70+0x3b/0x40 [ +0.000006] [] ? vfs_kern_mount+0x8d/0x110 [ +0.000004] [] btrfs_mount+0x8a3/0x9b0 [ +0.000005] [] ? alloc_pages_current+0xa3/0x170 [ +0.000006] [] mount_fs+0x34/0x1b0 [ +0.000004] [] vfs_kern_mount+0x62/0x110 [ +0.000004] [] do_mount+0x22e/0xac0 [ +0.000003] [] ? __get_free_pages+0x9/0x40 [ +0.000003] [] ? copy_mount_options+0x31/0x150 [ +0.000003] [] SyS_mount+0x7e/0xc0 [ +0.000006] [] system_call_fastpath+0x16/0x1b [ +0.000002] ---[ end trace 29fb4471bc9e3c49 ]--- Is this a known issue? I've searched the wiki and the bugtracker but can't find anything related. Some additional information. I've already checked to make sure that I don't have any files open for writing on the root filesystem using fuser + lsof, as well as trying to remount the root filesystem as read-only when it is already read-only. Remounting the filesystem as read-write works, but you cannot remount it as read-only afterwards either. I've tested this behavior on two of my computers with identical results, both are running kernel 3.16.1 on a single hard drive with data in single mode and metadata in dup mode. Both are raw btrfs on luks. -- Simon Thelen