[linux-lvm] Creating snapshot causes processes hang?

[James G. Sack (jim)]

> Date: Tue, 01 Nov 2005 16:02:55 -0600
> From: Kelly Sauke <ksauke at fastenal.com>
> Subject: Re: [linux-lvm] Creating snapshot causes processes hang?
> To: LVM general discussion and development <linux-lvm at redhat.com>
> Message-ID: <4367E60F.8020004 at fastenal.com>
> Content-Type: text/plain; charset=ISO-8859-1
> 
> http://www.redhat.com/archives/linux-lvm/2005-July/msg00117.html
> 

AHA! -- could this be a confirmation of what I have seen where lvremove
triggers the kcopyd BUG and consequent system deadlock?

(ref: my recent posting --  https://www.redhat.com/archives/linux-
lvm/2005-November/msg00002.html, where I report breakage upon lvremove
when there are 2 snapshots and i/o is occurring)


If so, do I also understand correctly that using unreleased patches and
some manual dmsetup commands might constitute a workaround?

I don't mind living with manual workarounds until snapshots is fixed,
but it would be wonderful to see an explicit recipe [for dummies, please
<grin>] for following the suggestions in the AGK july posting referenced
by ksauke, above), namely:

  "Further patches are needed, but those two plus correct dmsetup use
should avoid machine lockups."

In particular:
have any of the 18 patches shown at 
  ftp://sources.redhat.com/pub/dm/patches/2.6-unstable/2.6.12-
rc2/2.6.12-rc2-udm1/
gotten into 2.6.13 or 2.6.14, or into kernels blessed by Fedora? (eg,
FC4-1526, maybe)

And, could someone give me an example of "correct dmsetup" use? I
presume it involves suspend and resume -- but what else?

.. and in my case, what if there is an existing snapshot when I need to
create/remove a second one?



..jim