linux-kernel - Re: [RFC][PATCH 0/3] configfs: Make nested default groups lockdep-friendly

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Message-Id: <1211367577.6463.91.camel@lappy.programming.kicks-ass.net>
Date:	Wed, 21 May 2008 12:59:37 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Louis Rilling <Louis.Rilling@...labs.com>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Joel Becker <Joel.Becker@...cle.com>,
	linux-kernel@...r.kernel.org, ocfs2-devel@....oracle.com
Subject: Re: [RFC][PATCH 0/3] configfs: Make nested default
	groups	lockdep-friendly

On Wed, 2008-05-21 at 12:25 +0200, Louis Rilling wrote:

> > http://programming.kicks-ass.net/kernel-patches/concurrent-pagecache/23-rc1-rt/radix-concurrent-lockdep.patch
> 
> Thanks for pointing this out.
> 
> Yes this could solve part of the issue, at the price of duplicating the
> inode mutex class. However, this still does not solve the issue when
> deleting config_groups, since in that case all nodes of the tree are
> locked. Thinking about adding lockdep support for concurrent locking of
> the direct children of a node in a tree...

Why doesn't sysfs have this problem? - the code says configfs was
derived from sysfs.

Also, do you really need to hold all locks when removing something?
sound like a bit overdone. Also realise there is a maximum number of
held locks - various people have already requested it to be increased or
made dynamic. We're reluctant in doing so because we feel lock chains
should not be of unlimited length. The deeper the chains the bigger the
PI overhead etc..

As to modifying lockdep - it currently doesn't know about trees and
teaching it about them isn't easy.

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