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From: Robert Watson <rwatson@FreeBSD.org>
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To: Pete French <petefrench@ticketswitch.com>
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Cc: freebsd-stable@freebsd.org, drosih@rpi.edu, dchagin@freebsd.org,
	rblayzor.bulk@inoc.net
Subject: Re: Big problems with 7.1 locking up :-(
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On Fri, 16 Jan 2009, Pete French wrote:

>> hi, please type: show lock 0xffffff0001254d20 and then show thread 
>> 0xXXXXXXXXXXX where XXXXX is 'owner' of previous output.
>
> http://toybox.twisted.org.uk/~pete/71_pdns_lock.png
>
> That's in Power DNS - which is interesting because the one difference 
> between the boxes that lock and those which dont is that the locking ones 
> are serving DNS.

I rather feared as much.  Let's run down the path of "perhaps there's a 
problem with the new UDP locking code" for a bit and see where it takes us. 
Is it possible to run those boxes with WITNESS -- I believe that the fact that 
"show alllocks" is failing is because WITNESS isn't present.  The other thing 
we can do is revert UDP to using purely write locks -- the risk there is that 
it might change the timing but not actually resolve the bug, so if we can 
analyze it a bit using WITNESS first that would be useful.

Robert N M Watson
Computer Laboratory
University of Cambridge