Re: [linux-lvm] kernel panic on lvcreate

[Christopher Hawkins <chawkins@bplinux.com>]

It is reported here:

https://bugzilla.redhat.com/show_bug.cgi?id=539328

That is definitely the one. And it sounds like they have a potential fix... I have already emailed the developers there asking if I can help test their patch, so hopefully soon I can post back and report status. 

Christopher Hawkins

----- "Stuart D. Gathman" <stuart@bmsi.com> wrote:

> On Wed, 9 Dec 2009, Christopher Hawkins wrote:
> 
> > After some time I revisited this issue on a freshly installed Centos
> 5.4 box,
> > latest kernel (2.6.18-164.6.1.el5 ) and the panic is still
> reproducible. Any
> > time I create a snapshot of the root filesystem, kernel panics. The
> LVM HOWTO
> > says to post bug reports to this list. Is this the proper place?
> 
> Bummer.  I would post the bug on Centos bugzilla also.  Please post
> the
> bug number here if you do it (cause I'll get to it eventually).
> 
> Thanks for testing this.  I have the same problem, and have a new
> client
> to install by next year - so not much time to work on it.
> 
> Now that we know it is not yet fixed, we can form theories as to what
> is going wrong.  My guess is that the problem is caused by the fact
> that
> lvm is updating files in /etc/lvm on the root filesystem while taking
> the snapshot.  These updates are done by user space programs, so I
> would
> further speculate that *any* snapshot would crash if an update
> happened exactly
> when creating the snapshot - i.e. the atomic nature of snapshot
> creation has
> been broken.  The lvm user space probably does fsync() on files
> in /etc/lvm, which might be involved in triggering the crash.
> 
> We could test the first theory by moving /etc/lvm to another volume
> (I
> sometimes put it on /boot - a non LVM filesystem - for easier
> disaster
> recovery.) Naturally, I wouldn't go moving /etc/lvm on a production
> server.
> 
> Testing the second hypothesis is less certain, and would basically
> involve
> trying snapshots of LVs undergoing heavy updating.
> 
> -- 
> 	      Stuart D. Gathman <stuart@bmsi.com>
>     Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703
> 591-6154
> "Confutatis maledictis, flammis acribus addictis" - background song
> for
> a Microsoft sponsored "Where do you want to go from here?"
> commercial.
> 
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