Bug#419209: lvm2: Hangs during snapshot creation

[Steve Langasek]

On Wed, Mar 04, 2009 at 10:44:28AM +0100, Klaus Ethgen wrote:
> first of all, I raised the severity of the bug to critical as it makes
> the whole system break. Also I add debian-devel to Cc as the bug is very
> problematic and I wonder how lvm2 was able to get into lenny with that
> big problem!

Possibly because there are many people using LVM snapshotting who haven't
seen this bug?  I use schroot with LVM snapshots all the time on a server
running the lenny kernel, and have never seen this bug.

> I did use lvm1 with kernel 2.4 on etch for long time now using exact the
> same procedure which trigger the problem right now.

Which was not a supported configuration.  Linux 2.4 was supported in etch
only for purposes of upgrading, not for a running system.  Your decision to
run an unsupported system actually makes it harder to track down this bug,
since the only baseline we have for comparison in your case is a system with
none of the relevant components in common.

> Then with the release of lenny I start upgrading my stable systems. This
> involved a kernel upgrade as lenny only runs with the very instable kernel
> tree 2.6 and upgrade of the lvm metadata.

Claiming that the 2.6 kernel is unstable only undermines your credibility.

> Days after I noticed that apt-get install froze randomly and I had to
> reboot the system with a power cycle (reboot didn't work). First I was
> thinking about one of the many kernel bugs in 2.6 and tried the newest
> kernel from kernel.org. But the bug was still there. After several days
> I end in finding the problem in the LVM2 subsystem and two days later,
> today, I found this ug report and was very shocked! If I had know of it
> before I had never upgrade any of may stable systems to lenny! But now
> one of them is sticked on lenny as I know no way to revert the LVM back
> to LVM1.

The original bug reporter claims that the hang only occurs with newer
versions of the lvm2 userspace tools.  You could try downgrading to the etch
version of lvm2, to see whether this resolves the problem for you.

> Am Sa den 14. Apr 2007 um 12:53 schrieb Jean-Luc Coulon (f5ibh):
> > New lvm2 version (2.02.24) hangs during snapshot creation.
> > The lvmvreate process is not killeable at this point and the system need to be
> > reboted.

> That is the correct description. But more over the system will be
> unbootable at all! I have to run /etc/init.d/reboot stop by hand to hard
> reboot the system. A normal shutdown will end in a hanging system with
> no remote access at all. The only solution at that point is to
> powercycle the machine which is very problematic with remote system.

What does dmesg show for the system after the snapshot has hung?

-- 
Steve Langasek                   Give me a lever long enough and a Free OS
Debian Developer                   to set it on, and I can move the world.
Ubuntu Developer                                    http://www.debian.org/
slangasek at ubuntu.com                                     vorlon at debian.org