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Re: [Linux-cluster] Deadlock when using clvmd + OpenAIS + Corosync



On 11/01/10 09:32, Evan Broder wrote:
On Mon, Jan 11, 2010 at 4:03 AM, Christine Caulfield
<ccaulfie redhat com>  wrote:
On 08/01/10 22:58, Evan Broder wrote:

[please preserve the CC when replying, thanks]

Hi -
    We're attempting to setup a clvm (2.02.56) cluster using OpenAIS
(1.1.1) and Corosync (1.1.2). We've gotten bitten hard in the past by
crashes leaving DLM state around and forcing us to reboot our nodes,
so we're specifically looking for a solution that doesn't involve
in-kernel locking.

We're also running the Pacemaker OpenAIS service, as we're hoping to
use it for management of some other resources going forward.

We've managed to form the OpenAIS cluster, and get clvmd running on
both of our nodes. Operations using LVM succeed, so long as only one
operation runs at a time. However, if we attempt to run two operations
(say, one lvcreate on each host) at a time, they both hang, and both
clvmd processes appear to deadlock.

When they deadlock, it doesn't appear to affect the other clustering
processes - both corosync and pacemaker still report a fully formed
cluster, so it seems the issue is localized to clvmd.

I've looked at logs from corosync and pacemaker, and I've straced
various processes, but I don't want to blast a bunch of useless
information at the list. What information can I provide to make it
easier to debug and fix this deadlock?


To start with, the best logging to produce is the clvmd logs which can be
got with clvmd -d (see the man page for details). Ideally these should be
from all nodes in the cluster so they can be correlated. If you're still
using DLM then a dlm lock dump from all nodes is often helpful in
conjunction with the clvmd logs.

Sure, no problem. I've posted the logs from clvmd on both processes in
<http://web.mit.edu/broder/Public/clvmd/>. I've annotated them at a
few points with what I was doing - the annotations all start with "
", so they should be easy to spot.

One interesting thing was the output from lvcreate when I SIGKILLed
the clvmd process:

root black-mesa:~# lvcreate -L 1G -n broder-test-1 xenvg
   Error reading data from clvmd: Connection reset by peer
   Aborting. Failed to activate new LV to wipe the start of it.
   Error writing data to clvmd: Broken pipe
   Unable to deactivate failed new LV. Manual intervention required.
   Error writing data to clvmd: Broken pipe
   Internal error: Volume Group xenvg was not unlocked
   Device '/dev/sdb' has been left open.
   Device '/dev/sdc' has been left open.
   Device '/dev/sdc' has been left open.
   Device '/dev/sdb' has been left open.


That's perfectly normal for LVM if you killed clvmd with SIGKILL

I'm not entirely sure what to make of that, or how worried I should
be. After I killed clvmd and restarted corosync, broder-test-1 (the
first lvcreate I started) did seem to exist, although I didn't look
too hard at it.

Also, did you know it's possible to use clvmd without the DLM? The -I
openais option will tell it to use the Lck service in userspace - though if
there are DLM bugs I think we'd like to fix them if possible ;-)

I suspect that the DLM bugs we ran into were all from using old
software - it just left a bit of a bitter taste in our mouth when we
were left with no way to recover from problems. We  built the clvmd
we're using now without support for any clustering infrastructure but
openais, so we should always be using the Lck service.


If you were using the DLM in RHEL4 (or equivalent) then that doesn't entirely surprise me, it was written and tested largely to support GFS and other applications were a bit of an afterthought, sadly. The new upstream DLM is a huge improvement.

I'll try and get some time to look at your logs, thanks. But it might not be today.

Chrissie


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