[Vserver] Soft Lock Problem

From: Ben Green <ben_at_bristolwireless.net>
Date: Tue 17 Jul 2007 - 09:11:07 BST
Message-ID: <op.tvlnoteu0bw284@spinach.lan>

I had a brief chat with people on the IRC channel about a soft lockup I was having with vserver systems. I said I would produce a report of the problem. This is a very limited report, but you are all welcome to ask for more info.

Basically we have 2 machines, more or less identical. The error has appeared on the following Debian kernels 2.6.18, 2.6.20, 2.6.21. All are vserver-amd64. System is an AMD64 with FX-62 processors. 4Gb RAM.

The system are used all the time, so I can't really experiment too much except on Sundays. The symptoms are thus:

1/ machine freezes for a short amount of time, 2 or three seconds.
2/ nothing unusual for the next 5 to 10 seconds
3/ a soft lock up occurs and is reported, freezing everything

The process that dies is within seemingly random contexts, including the host one. The lock ups occur with a regularity of between once every day and once every three days. They have always happened when the servers are under some kind of load, either rsyncing or with lots of users.

A further condition now seems to be having 2 specific vservers running on one machine. One is our local Debian repository, and the other is our LTSP server, which has access to some local hardware and some no-standard capabilities set. Now that these servers are run on seperate machines, there have been no lock ups for 2 weeks. The LTSP server necessarily uses lots and lots of RAM. The repository pull lots of file in to memory, but should really need that much to operate. Both have no limits set currently.

I am in the process of checking out the latest Debian kernel (which is 2.6.21.5 with the stable vserver patch), but haven't got round to sorting out compiling my own yet, or loading up the new Debian kernel system so as to cause the crash. I will do both of these some Sunday soon, armed with a new distcc set up. I also hope to try various limits to see if that helps the 2 vserver guest co-exist in peace.

Well, there's a bit of reporting.

Cheers,

-- 
 From Ben Green
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Received on Tue Jul 17 09:15:09 2007
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