From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [10.34.131.133] (dhcp131-133.brq.redhat.com [10.34.131.133]) by int-mx12.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id r78A1iPO024521 for ; Thu, 8 Aug 2013 06:01:44 -0400 Message-ID: <52036C86.3040702@redhat.com> Date: Thu, 08 Aug 2013 12:01:42 +0200 From: Zdenek Kabelac MIME-Version: 1.0 References: <20130806173719.GB15184@mail.waldi.eu.org> <520211BB.2040301@pse-consulting.de> <5202164B.5010302@redhat.com> <52028170.1010000@pse-consulting.de> In-Reply-To: <52028170.1010000@pse-consulting.de> Content-Transfer-Encoding: 7bit Subject: Re: [linux-lvm] Missing error handling in lv_snapshot_remove Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: linux-lvm@redhat.com Dne 7.8.2013 19:18, Andreas Pflug napsal(a): > On 08/07/13 11:41, Zdenek Kabelac wrote: >> Dne 7.8.2013 11:22, Andreas Pflug napsal(a): >>> Am 06.08.13 19:37, schrieb Bastian Blank: >>>> Hi >>>> >>>> I tried to tackle a particular bug that shows up in Debian for some time >>>> now. Some blamed the udev rules and I still can't completely rule them >>>> out. But this triggers a much worse bug in the error cleanup of the >>>> snapshot remove. I reproduced this with Debian/Linux 3.2.46/LVM 2.02.99 >>>> without udevd running and Fedora 19/LVM 2.02.98-10.fc19. >>>> >>>> On snapshot removal, LVM first converts the device into a regular LV >>>> (lv_remove_snapshot) and in a second step removes this LV >>>> (lv_remove_single). Is there a reason for this two step removal? An >>>> error during removal leaves a non-snapshot LV behind. >>> Ah, this explains why sometimes my backup stops: I take a snapshot, >>> rsync the stuff and remove the snapshot with a daily cron job, but I >>> observed twice that a non-snapshot volume named like a backup snapshot >>> was lingering around, preventing the script to work. So this is no >>> exotic corner case, but happens in real life. >>> >>> I observe this since I dist-upgraded to wheezy. >>> >> >> Because Debian is using non-upstream udev rules. >> >> With upstream udev rules with standard real-life use, this situation >> cannot happen - since these rules are constructed to play better with >> udev WATCH rule. > > Hm, does udev play a role on this at all? Without having dived the code, I'd > assume udev has only to do with creation and deletion of /dev/mapper/... > and/or /dev/vgname/... devices (upon lvchange -aX), but not with lvm metadata > manipulation. Udev attempts to update it device database after any change event (you could observe its work with udevadm monitor) So in your case - you unmount filesystem -> close device -> fires WATCH event with some randomly delayed (systemd)udevd scan machism - so in unpredictable moment blkid opens device and scans its sectors (keeping device open and interfering with deactivate operation). For this short-time opens there is now built-in retry which tries to deactivate device several times when it's known device is not mounted. Zdenek