From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.web.de ([212.227.17.12]:50581 "EHLO mout.web.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752885AbaLAVp3 convert rfc822-to-8bit (ORCPT ); Mon, 1 Dec 2014 16:45:29 -0500 Message-ID: <547CE175.6060409@web.de> Date: Mon, 01 Dec 2014 22:45:25 +0100 From: Konstantin MIME-Version: 1.0 To: MegaBrutal , linux-btrfs Subject: Re: PROBLEM: #89121 BTRFS mixes up mounted devices with their snapshots References: In-Reply-To: Content-Type: text/plain; charset=UTF-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: MegaBrutal schrieb am 01.12.2014 um 13:56: > Hi all, > > I've reported the bug I've previously posted about in "BTRFS messes up > snapshot LV with origin" in the Kernel Bug Tracker. > https://bugzilla.kernel.org/show_bug.cgi?id=89121 Hi MegaBrutal. If I understand your report correctly, I can give you another example where this bug is appearing. It is so bad that it leads to freezing the system and I'm quite sure it's the same thing. I was thinking about filing a bug but didn't have the time for that yet. Maybe you could add this case to your bug report as well. The bug appears also when using mdadm RAID1 - when one of the drives is detached from the array then the OS discovers it and after a while (not directly, it takes several minutes) it appears under /proc/mounts: instead of /dev/md0p1 I see there /dev/sdb1. And usually after some hour or so (depending on system workload) the PC completely freezes. So discussion about the uniqueness of UUIDs or not, a crashing kernel is telling me that there is a serious bug. While in my case detaching was intentional, there are several real possibilities when a RAID1 disk can get detached and currently this leads to crashing the server when using BTRFS. That not what is intended when using RAID ;-). In my case I wanted to do something which was working perfectly all the years before with all other file systems - checking the file system of the root disk while the server is running. The procedure is simple: 1. detach one of the disks 2. do fsck on the disk device 3. mdadm --zero-superblock on the device so it gets completely rewritten 4. mdadm --add it to the array There were some surprises with BTRFS - if 2. is not done directly after 1. btrfsck refuses to check the disk as it is reported to be mounted by /proc/mounts. And while 2. or even after finishing it the system was freezing. If I got to get to 4. fast enough everything was OK, but again, that's not what I expect from a good operating system. Any objections? Konstantin