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To: Marcel Moolenaar <marcel@xcllnt.net>
Subject: Re: svn commit: r250411 - in head/sys: conf kern sys 
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Date: Sat, 11 May 2013 14:08:58 -0700
From: Kirk McKusick <mckusick@mckusick.com>
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As a filesystem developer, I am very dependent on being able to get
vnode lock order reversal LORs. While I have long wanted the ability
to individually identify the benign ones (such as vnode + dirhash
which your fix will not eliminate since dirhash is not a vnode),
that facility exists only for mutexes at the moment. This latest
flurry of emails on your change may hasten the day when Attilio's
extension gets added to make the identity for other types of locks
available.

In the meantime, I do understand your need to silence the offending
benign messages. But I would like to suggest that instead of making
it a compile time option, that you change it to be conditional using
a sysctl such as debug.witness.novnodes (you would need to add the
witness debug subclass as I don't think that it currently exists).
You can set the default to be enabled (e.g., suppressed vnode warnings).
This way if I get a filesystem deadlock bug reported to me, I can ask
the user to reenable vnode witness warnings without having to have
them build a whole new kernel.

	Kirk McKusick